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| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="coroutine.coroutine.asymmetric"></a><a class="link" href="asymmetric.html" title="Asymmetric coroutine">Asymmetric coroutine</a> |
| </h3></div></div></div> |
| <div class="toc"><dl class="toc"> |
| <dt><span class="section"><a href="asymmetric/pull_coro.html">Class <code class="computeroutput"><span class="identifier">asymmetric_coroutine</span><span class="special"><>::</span><span class="identifier">pull_type</span></code></a></span></dt> |
| <dt><span class="section"><a href="asymmetric/push_coro.html">Class <code class="computeroutput"><span class="identifier">asymmetric_coroutine</span><span class="special"><>::</span><span class="identifier">push_type</span></code></a></span></dt> |
| </dl></div> |
| <p> |
| Two asymmetric coroutine types - <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> |
| and <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> - provide |
| a unidirectional transfer of data. |
| </p> |
| <h5> |
| <a name="coroutine.coroutine.asymmetric.h0"></a> |
| <span class="phrase"><a name="coroutine.coroutine.asymmetric._emphasis_asymmetric_coroutine_lt__gt___pull_type__emphasis_"></a></span><a class="link" href="asymmetric.html#coroutine.coroutine.asymmetric._emphasis_asymmetric_coroutine_lt__gt___pull_type__emphasis_"><span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span></a> |
| </h5> |
| <p> |
| <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> transfers data |
| from another execution context (== pulled-from). The template parameter defines |
| the transferred parameter type. The constructor of <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> |
| takes a function (<span class="emphasis"><em>coroutine-function</em></span>) accepting a reference |
| to an <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> as argument. |
| Instantiating an <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> |
| passes the control of execution to <span class="emphasis"><em>coroutine-function</em></span> |
| and a complementary <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> |
| is synthesized by the library and passed as reference to <span class="emphasis"><em>coroutine-function</em></span>. |
| </p> |
| <p> |
| This kind of coroutine provides <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::operator()</em></span>. |
| This method only switches context; it transfers no data. |
| </p> |
| <p> |
| <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> provides input |
| iterators (<span class="emphasis"><em>asymmetric_coroutine<>::pull_type::iterator</em></span>) |
| and <span class="emphasis"><em>std::begin()</em></span>/<span class="emphasis"><em>std::end()</em></span> are |
| overloaded. The increment-operation switches the context and transfers data. |
| </p> |
| <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">asymmetric_coroutine</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">pull_type</span> <span class="identifier">source</span><span class="special">(</span> |
| <span class="special">[&](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">asymmetric_coroutine</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">push_type</span><span class="special">&</span> <span class="identifier">sink</span><span class="special">){</span> |
| <span class="keyword">int</span> <span class="identifier">first</span><span class="special">=</span><span class="number">1</span><span class="special">,</span><span class="identifier">second</span><span class="special">=</span><span class="number">1</span><span class="special">;</span> |
| <span class="identifier">sink</span><span class="special">(</span><span class="identifier">first</span><span class="special">);</span> |
| <span class="identifier">sink</span><span class="special">(</span><span class="identifier">second</span><span class="special">);</span> |
| <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span><span class="special">=</span><span class="number">0</span><span class="special">;</span><span class="identifier">i</span><span class="special"><</span><span class="number">8</span><span class="special">;++</span><span class="identifier">i</span><span class="special">){</span> |
| <span class="keyword">int</span> <span class="identifier">third</span><span class="special">=</span><span class="identifier">first</span><span class="special">+</span><span class="identifier">second</span><span class="special">;</span> |
| <span class="identifier">first</span><span class="special">=</span><span class="identifier">second</span><span class="special">;</span> |
| <span class="identifier">second</span><span class="special">=</span><span class="identifier">third</span><span class="special">;</span> |
| <span class="identifier">sink</span><span class="special">(</span><span class="identifier">third</span><span class="special">);</span> |
| <span class="special">}</span> |
| <span class="special">});</span> |
| |
| <span class="keyword">for</span><span class="special">(</span><span class="keyword">auto</span> <span class="identifier">i</span><span class="special">:</span><span class="identifier">source</span><span class="special">)</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">i</span> <span class="special"><<</span> <span class="string">" "</span><span class="special">;</span> |
| |
| <span class="identifier">output</span><span class="special">:</span> |
| <span class="number">1</span> <span class="number">1</span> <span class="number">2</span> <span class="number">3</span> <span class="number">5</span> <span class="number">8</span> <span class="number">13</span> <span class="number">21</span> <span class="number">34</span> <span class="number">55</span> |
| </pre> |
| <p> |
| In this example an <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> |
| is created in the main execution context taking a lambda function (== <span class="emphasis"><em>coroutine-function</em></span>) |
| which calculates Fibonacci numbers in a simple <span class="emphasis"><em>for</em></span>-loop. |
| The <span class="emphasis"><em>coroutine-function</em></span> is executed in a newly created |
| execution context which is managed by the instance of <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span>. |
| An <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> is automatically |
| generated by the library and passed as reference to the lambda function. |
| Each time the lambda function calls <span class="emphasis"><em>asymmetric_coroutine<>::push_type::operator()</em></span> |
| with another Fibonacci number, <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> |
| transfers it back to the main execution context. The local state of <span class="emphasis"><em>coroutine-function</em></span> |
| is preserved and will be restored upon transferring execution control back |
| to <span class="emphasis"><em>coroutine-function</em></span> to calculate the next Fibonacci |
| number. Because <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> |
| provides input iterators and <span class="emphasis"><em>std::begin()</em></span>/<span class="emphasis"><em>std::end()</em></span> |
| are overloaded, a <span class="emphasis"><em>range-based for</em></span>-loop can be used to |
| iterate over the generated Fibonacci numbers. |
| </p> |
| <h5> |
| <a name="coroutine.coroutine.asymmetric.h1"></a> |
| <span class="phrase"><a name="coroutine.coroutine.asymmetric._emphasis_asymmetric_coroutine_lt__gt___push_type__emphasis_"></a></span><a class="link" href="asymmetric.html#coroutine.coroutine.asymmetric._emphasis_asymmetric_coroutine_lt__gt___push_type__emphasis_"><span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span></a> |
| </h5> |
| <p> |
| <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> transfers data |
| to the other execution context (== pushed-to). The template parameter defines |
| the transferred parameter type. The constructor of <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> |
| takes a function (<span class="emphasis"><em>coroutine-function</em></span>) accepting a reference |
| to an <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> as argument. |
| In contrast to <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span>, |
| instantiating an <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> |
| does not pass the control of execution to <span class="emphasis"><em>coroutine-function</em></span> |
| - instead the first call of <span class="emphasis"><em>asymmetric_coroutine<>::push_type::operator()</em></span> |
| synthesizes a complementary <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> |
| and passes it as reference to <span class="emphasis"><em>coroutine-function</em></span>. |
| </p> |
| <p> |
| The <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> interface |
| does not contain a <span class="emphasis"><em>get()</em></span>-function: you can not retrieve |
| values from another execution context with this kind of coroutine. |
| </p> |
| <p> |
| <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> provides output |
| iterators (<span class="emphasis"><em>asymmetric_coroutine<>::push_type::iterator</em></span>) |
| and <span class="emphasis"><em>std::begin()</em></span>/<span class="emphasis"><em>std::end()</em></span> are |
| overloaded. The increment-operation switches the context and transfers data. |
| </p> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">FinalEOL</span><span class="special">{</span> |
| <span class="special">~</span><span class="identifier">FinalEOL</span><span class="special">(){</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">};</span> |
| |
| <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">num</span><span class="special">=</span><span class="number">5</span><span class="special">,</span> <span class="identifier">width</span><span class="special">=</span><span class="number">15</span><span class="special">;</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">asymmetric_coroutine</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>::</span><span class="identifier">push_type</span> <span class="identifier">writer</span><span class="special">(</span> |
| <span class="special">[&](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">asymmetric_coroutine</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>::</span><span class="identifier">pull_type</span><span class="special">&</span> <span class="identifier">in</span><span class="special">){</span> |
| <span class="comment">// finish the last line when we leave by whatever means</span> |
| <span class="identifier">FinalEOL</span> <span class="identifier">eol</span><span class="special">;</span> |
| <span class="comment">// pull values from upstream, lay them out 'num' to a line</span> |
| <span class="keyword">for</span> <span class="special">(;;){</span> |
| <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span><span class="special">=</span><span class="number">0</span><span class="special">;</span><span class="identifier">i</span><span class="special"><</span><span class="identifier">num</span><span class="special">;++</span><span class="identifier">i</span><span class="special">){</span> |
| <span class="comment">// when we exhaust the input, stop</span> |
| <span class="keyword">if</span><span class="special">(!</span><span class="identifier">in</span><span class="special">)</span> <span class="keyword">return</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">setw</span><span class="special">(</span><span class="identifier">width</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">in</span><span class="special">.</span><span class="identifier">get</span><span class="special">();</span> |
| <span class="comment">// now that we've handled this item, advance to next</span> |
| <span class="identifier">in</span><span class="special">();</span> |
| <span class="special">}</span> |
| <span class="comment">// after 'num' items, line break</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">});</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">></span> <span class="identifier">words</span><span class="special">{</span> |
| <span class="string">"peas"</span><span class="special">,</span> <span class="string">"porridge"</span><span class="special">,</span> <span class="string">"hot"</span><span class="special">,</span> <span class="string">"peas"</span><span class="special">,</span> |
| <span class="string">"porridge"</span><span class="special">,</span> <span class="string">"cold"</span><span class="special">,</span> <span class="string">"peas"</span><span class="special">,</span> <span class="string">"porridge"</span><span class="special">,</span> |
| <span class="string">"in"</span><span class="special">,</span> <span class="string">"the"</span><span class="special">,</span> <span class="string">"pot"</span><span class="special">,</span> <span class="string">"nine"</span><span class="special">,</span> |
| <span class="string">"days"</span><span class="special">,</span> <span class="string">"old"</span> <span class="special">};</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">copy</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">begin</span><span class="special">(</span><span class="identifier">words</span><span class="special">),</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">end</span><span class="special">(</span><span class="identifier">words</span><span class="special">),</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">begin</span><span class="special">(</span><span class="identifier">writer</span><span class="special">));</span> |
| |
| <span class="identifier">output</span><span class="special">:</span> |
| <span class="identifier">peas</span> <span class="identifier">porridge</span> <span class="identifier">hot</span> <span class="identifier">peas</span> <span class="identifier">porridge</span> |
| <span class="identifier">cold</span> <span class="identifier">peas</span> <span class="identifier">porridge</span> <span class="identifier">in</span> <span class="identifier">the</span> |
| <span class="identifier">pot</span> <span class="identifier">nine</span> <span class="identifier">days</span> <span class="identifier">old</span> |
| </pre> |
| <p> |
| In this example an <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> |
| is created in the main execution context accepting a lambda function (== |
| <span class="emphasis"><em>coroutine-function</em></span>) which requests strings and lays |
| out 'num' of them on each line. This demonstrates the inversion of control |
| permitted by coroutines. Without coroutines, a utility function to perform |
| the same job would necessarily accept each new value as a function parameter, |
| returning after processing that single value. That function would depend |
| on a static state variable. A <span class="emphasis"><em>coroutine-function</em></span>, however, |
| can request each new value as if by calling a function -- even though its |
| caller also passes values as if by calling a function. The <span class="emphasis"><em>coroutine-function</em></span> |
| is executed in a newly created execution context which is managed by the |
| instance of <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span>. |
| The main execution context passes the strings to the <span class="emphasis"><em>coroutine-function</em></span> |
| by calling <span class="emphasis"><em>asymmetric_coroutine<>::push_type::operator()</em></span>. |
| An <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> instance |
| is automatically generated by the library and passed as reference to the |
| lambda function. The <span class="emphasis"><em>coroutine-function</em></span> accesses the |
| strings passed from the main execution context by calling <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::get()</em></span> |
| and lays those strings out on <span class="emphasis"><em>std::cout</em></span> according the |
| parameters 'num' and 'width'. The local state of <span class="emphasis"><em>coroutine-function</em></span> |
| is preserved and will be restored after transferring execution control back |
| to <span class="emphasis"><em>coroutine-function</em></span>. Because <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> |
| provides output iterators and <span class="emphasis"><em>std::begin()</em></span>/<span class="emphasis"><em>std::end()</em></span> |
| are overloaded, the <span class="emphasis"><em>std::copy</em></span> algorithm can be used |
| to iterate over the vector containing the strings and pass them one by one |
| to the coroutine. |
| </p> |
| <h5> |
| <a name="coroutine.coroutine.asymmetric.h2"></a> |
| <span class="phrase"><a name="coroutine.coroutine.asymmetric.coroutine_function"></a></span><a class="link" href="asymmetric.html#coroutine.coroutine.asymmetric.coroutine_function">coroutine-function</a> |
| </h5> |
| <p> |
| The <span class="emphasis"><em>coroutine-function</em></span> returns <span class="emphasis"><em>void</em></span> |
| and takes its counterpart-coroutine as argument, so that using the coroutine |
| passed as argument to <span class="emphasis"><em>coroutine-function</em></span> is the only |
| way to transfer data and execution control back to the caller. Both coroutine |
| types take the same template argument. For <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> |
| the <span class="emphasis"><em>coroutine-function</em></span> is entered at <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> |
| construction. For <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> |
| the <span class="emphasis"><em>coroutine-function</em></span> is not entered at <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> |
| construction but entered by the first invocation of <span class="emphasis"><em>asymmetric_coroutine<>::push_type::operator()</em></span>. |
| After execution control is returned from <span class="emphasis"><em>coroutine-function</em></span> |
| the state of the coroutine can be checked via <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::operator |
| bool</em></span> returning <code class="computeroutput"><span class="keyword">true</span></code> |
| if the coroutine is still valid (<span class="emphasis"><em>coroutine-function</em></span> |
| has not terminated). Unless the first template parameter is <code class="computeroutput"><span class="keyword">void</span></code>, <code class="computeroutput"><span class="keyword">true</span></code> |
| also implies that a data value is available. |
| </p> |
| <h5> |
| <a name="coroutine.coroutine.asymmetric.h3"></a> |
| <span class="phrase"><a name="coroutine.coroutine.asymmetric.passing_data_from_a_pull_coroutine_to_main_context"></a></span><a class="link" href="asymmetric.html#coroutine.coroutine.asymmetric.passing_data_from_a_pull_coroutine_to_main_context">passing |
| data from a pull-coroutine to main-context</a> |
| </h5> |
| <p> |
| In order to transfer data from an <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> |
| to the main-context the framework synthesizes an <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> |
| associated with the <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> |
| instance in the main-context. The synthesized <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> |
| is passed as argument to <span class="emphasis"><em>coroutine-function</em></span>. The <span class="emphasis"><em>coroutine-function</em></span> |
| must call this <span class="emphasis"><em>asymmetric_coroutine<>::push_type::operator()</em></span> |
| in order to transfer each data value back to the main-context. In the main-context, |
| the <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::operator bool</em></span> |
| determines whether the coroutine is still valid and a data value is available |
| or <span class="emphasis"><em>coroutine-function</em></span> has terminated (<span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> |
| is invalid; no data value available). Access to the transferred data value |
| is given by <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::get()</em></span>. |
| </p> |
| <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">asymmetric_coroutine</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">pull_type</span> <span class="identifier">source</span><span class="special">(</span> <span class="comment">// constructor enters coroutine-function</span> |
| <span class="special">[&](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">asymmetric_coroutine</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">push_type</span><span class="special">&</span> <span class="identifier">sink</span><span class="special">){</span> |
| <span class="identifier">sink</span><span class="special">(</span><span class="number">1</span><span class="special">);</span> <span class="comment">// push {1} back to main-context</span> |
| <span class="identifier">sink</span><span class="special">(</span><span class="number">1</span><span class="special">);</span> <span class="comment">// push {1} back to main-context</span> |
| <span class="identifier">sink</span><span class="special">(</span><span class="number">2</span><span class="special">);</span> <span class="comment">// push {2} back to main-context</span> |
| <span class="identifier">sink</span><span class="special">(</span><span class="number">3</span><span class="special">);</span> <span class="comment">// push {3} back to main-context</span> |
| <span class="identifier">sink</span><span class="special">(</span><span class="number">5</span><span class="special">);</span> <span class="comment">// push {5} back to main-context</span> |
| <span class="identifier">sink</span><span class="special">(</span><span class="number">8</span><span class="special">);</span> <span class="comment">// push {8} back to main-context</span> |
| <span class="special">});</span> |
| |
| <span class="keyword">while</span><span class="special">(</span><span class="identifier">source</span><span class="special">){</span> <span class="comment">// test if pull-coroutine is valid</span> |
| <span class="keyword">int</span> <span class="identifier">ret</span><span class="special">=</span><span class="identifier">source</span><span class="special">.</span><span class="identifier">get</span><span class="special">();</span> <span class="comment">// access data value</span> |
| <span class="identifier">source</span><span class="special">();</span> <span class="comment">// context-switch to coroutine-function</span> |
| <span class="special">}</span> |
| </pre> |
| <h5> |
| <a name="coroutine.coroutine.asymmetric.h4"></a> |
| <span class="phrase"><a name="coroutine.coroutine.asymmetric.passing_data_from_main_context_to_a_push_coroutine"></a></span><a class="link" href="asymmetric.html#coroutine.coroutine.asymmetric.passing_data_from_main_context_to_a_push_coroutine">passing |
| data from main-context to a push-coroutine</a> |
| </h5> |
| <p> |
| In order to transfer data to an <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> |
| from the main-context the framework synthesizes an <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> |
| associated with the <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> |
| instance in the main-context. The synthesized <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> |
| is passed as argument to <span class="emphasis"><em>coroutine-function</em></span>. The main-context |
| must call this <span class="emphasis"><em>asymmetric_coroutine<>::push_type::operator()</em></span> |
| in order to transfer each data value into the <span class="emphasis"><em>coroutine-function</em></span>. |
| Access to the transferred data value is given by <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::get()</em></span>. |
| </p> |
| <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">asymmetric_coroutine</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">push_type</span> <span class="identifier">sink</span><span class="special">(</span> <span class="comment">// constructor does NOT enter coroutine-function</span> |
| <span class="special">[&](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">asymmetric_coroutine</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">pull_type</span><span class="special">&</span> <span class="identifier">source</span><span class="special">){</span> |
| <span class="keyword">for</span> <span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span><span class="special">:</span><span class="identifier">source</span><span class="special">)</span> <span class="special">{</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">i</span> <span class="special"><<</span> <span class="string">" "</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">});</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">v</span><span class="special">{</span><span class="number">1</span><span class="special">,</span><span class="number">1</span><span class="special">,</span><span class="number">2</span><span class="special">,</span><span class="number">3</span><span class="special">,</span><span class="number">5</span><span class="special">,</span><span class="number">8</span><span class="special">,</span><span class="number">13</span><span class="special">,</span><span class="number">21</span><span class="special">,</span><span class="number">34</span><span class="special">,</span><span class="number">55</span><span class="special">};</span> |
| <span class="keyword">for</span><span class="special">(</span> <span class="keyword">int</span> <span class="identifier">i</span><span class="special">:</span><span class="identifier">v</span><span class="special">){</span> |
| <span class="identifier">sink</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span> <span class="comment">// push {i} to coroutine-function</span> |
| <span class="special">}</span> |
| </pre> |
| <h5> |
| <a name="coroutine.coroutine.asymmetric.h5"></a> |
| <span class="phrase"><a name="coroutine.coroutine.asymmetric.accessing_parameters"></a></span><a class="link" href="asymmetric.html#coroutine.coroutine.asymmetric.accessing_parameters">accessing |
| parameters</a> |
| </h5> |
| <p> |
| Parameters returned from or transferred to the <span class="emphasis"><em>coroutine-function</em></span> |
| can be accessed with <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::get()</em></span>. |
| </p> |
| <p> |
| Splitting-up the access of parameters from context switch function enables |
| to check if <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> |
| is valid after return from <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::operator()</em></span>, |
| e.g. <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> has values |
| and <span class="emphasis"><em>coroutine-function</em></span> has not terminated. |
| </p> |
| <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">asymmetric_coroutine</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">tuple</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span><span class="keyword">int</span><span class="special">>>::</span><span class="identifier">push_type</span> <span class="identifier">sink</span><span class="special">(</span> |
| <span class="special">[&](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">asymmetric_coroutine</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">tuple</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span><span class="keyword">int</span><span class="special">>>::</span><span class="identifier">pull_type</span><span class="special">&</span> <span class="identifier">source</span><span class="special">){</span> |
| <span class="comment">// access tuple {7,11}; x==7 y==1</span> |
| <span class="keyword">int</span> <span class="identifier">x</span><span class="special">,</span><span class="identifier">y</span><span class="special">;</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">x</span><span class="special">,</span><span class="identifier">y</span><span class="special">)=</span><span class="identifier">source</span><span class="special">.</span><span class="identifier">get</span><span class="special">();</span> |
| <span class="special">});</span> |
| |
| <span class="identifier">sink</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_tuple</span><span class="special">(</span><span class="number">7</span><span class="special">,</span><span class="number">11</span><span class="special">));</span> |
| </pre> |
| <h5> |
| <a name="coroutine.coroutine.asymmetric.h6"></a> |
| <span class="phrase"><a name="coroutine.coroutine.asymmetric.exceptions"></a></span><a class="link" href="asymmetric.html#coroutine.coroutine.asymmetric.exceptions">exceptions</a> |
| </h5> |
| <p> |
| An exception thrown inside an <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span>'s |
| <span class="emphasis"><em>coroutine-function</em></span> before its first call to <span class="emphasis"><em>asymmetric_coroutine<>::push_type::operator()</em></span> |
| will be re-thrown by the <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> |
| constructor. After an <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span>'s |
| <span class="emphasis"><em>coroutine-function</em></span>'s first call to <span class="emphasis"><em>asymmetric_coroutine<>::push_type::operator()</em></span>, |
| any subsequent exception inside that <span class="emphasis"><em>coroutine-function</em></span> |
| will be re-thrown by <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::operator()</em></span>. |
| <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::get()</em></span> does |
| not throw. |
| </p> |
| <p> |
| An exception thrown inside an <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span>'s |
| <span class="emphasis"><em>coroutine-function</em></span> will be re-thrown by <span class="emphasis"><em>asymmetric_coroutine<>::push_type::operator()</em></span>. |
| </p> |
| <div class="important"><table border="0" summary="Important"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../../doc/src/images/important.png"></td> |
| <th align="left">Important</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| Code executed by <span class="emphasis"><em>coroutine-function</em></span> must not prevent |
| the propagation of the <span class="emphasis"><em>detail::forced_unwind</em></span> exception. |
| Absorbing that exception will cause stack unwinding to fail. Thus, any |
| code that catches all exceptions must re-throw any pending <span class="emphasis"><em>detail::forced_unwind</em></span> |
| exception. |
| </p></td></tr> |
| </table></div> |
| <pre class="programlisting"><span class="keyword">try</span> <span class="special">{</span> |
| <span class="comment">// code that might throw</span> |
| <span class="special">}</span> <span class="keyword">catch</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">detail</span><span class="special">::</span><span class="identifier">forced_unwind</span><span class="special">&)</span> <span class="special">{</span> |
| <span class="keyword">throw</span><span class="special">;</span> |
| <span class="special">}</span> <span class="keyword">catch</span><span class="special">(...)</span> <span class="special">{</span> |
| <span class="comment">// possibly not re-throw pending exception</span> |
| <span class="special">}</span> |
| </pre> |
| <div class="important"><table border="0" summary="Important"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../../doc/src/images/important.png"></td> |
| <th align="left">Important</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| Do not jump from inside a catch block and than re-throw the exception in |
| another execution context. |
| </p></td></tr> |
| </table></div> |
| <h5> |
| <a name="coroutine.coroutine.asymmetric.h7"></a> |
| <span class="phrase"><a name="coroutine.coroutine.asymmetric.stack_unwinding"></a></span><a class="link" href="asymmetric.html#coroutine.coroutine.asymmetric.stack_unwinding">Stack |
| unwinding</a> |
| </h5> |
| <p> |
| Sometimes it is necessary to unwind the stack of an unfinished coroutine |
| to destroy local stack variables so they can release allocated resources |
| (RAII pattern). The <code class="computeroutput"><span class="identifier">attributes</span></code> |
| argument of the coroutine constructor indicates whether the destructor should |
| unwind the stack (stack is unwound by default). |
| </p> |
| <p> |
| Stack unwinding assumes the following preconditions: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> |
| <li class="listitem"> |
| The coroutine is not <span class="emphasis"><em>not-a-coroutine</em></span> |
| </li> |
| <li class="listitem"> |
| The coroutine is not complete |
| </li> |
| <li class="listitem"> |
| The coroutine is not running |
| </li> |
| <li class="listitem"> |
| The coroutine owns a stack |
| </li> |
| </ul></div> |
| <p> |
| After unwinding, a <span class="emphasis"><em>coroutine</em></span> is complete. |
| </p> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">X</span> <span class="special">{</span> |
| <span class="identifier">X</span><span class="special">(){</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special"><<</span><span class="string">"X()"</span><span class="special"><<</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="special">~</span><span class="identifier">X</span><span class="special">(){</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special"><<</span><span class="string">"~X()"</span><span class="special"><<</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">};</span> |
| |
| <span class="special">{</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">asymmetric_coroutine</span><span class="special"><</span><span class="keyword">void</span><span class="special">>::</span><span class="identifier">push_type</span> <span class="identifier">sink</span><span class="special">(</span> |
| <span class="special">[&](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">asymmetric_coroutine</span><span class="special"><</span><span class="keyword">void</span><span class="special">>::</span><span class="identifier">pull_type</span><span class="special">&</span> <span class="identifier">source</span><span class="special">){</span> |
| <span class="identifier">X</span> <span class="identifier">x</span><span class="special">;</span> |
| <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span><span class="special">=</span><span class="number">0</span><span class="special">;;++</span><span class="identifier">i</span><span class="special">){</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special"><<</span><span class="string">"fn(): "</span><span class="special"><<</span><span class="identifier">i</span><span class="special"><<</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="comment">// transfer execution control back to main()</span> |
| <span class="identifier">source</span><span class="special">();</span> |
| <span class="special">}</span> |
| <span class="special">});</span> |
| |
| <span class="identifier">sink</span><span class="special">();</span> |
| <span class="identifier">sink</span><span class="special">();</span> |
| <span class="identifier">sink</span><span class="special">();</span> |
| <span class="identifier">sink</span><span class="special">();</span> |
| <span class="identifier">sink</span><span class="special">();</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special"><<</span><span class="string">"sink is complete: "</span><span class="special"><<</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">boolalpha</span><span class="special"><<!</span><span class="identifier">sink</span><span class="special"><<</span><span class="string">"\n"</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="identifier">output</span><span class="special">:</span> |
| <span class="identifier">X</span><span class="special">()</span> |
| <span class="identifier">fn</span><span class="special">():</span> <span class="number">0</span> |
| <span class="identifier">fn</span><span class="special">():</span> <span class="number">1</span> |
| <span class="identifier">fn</span><span class="special">():</span> <span class="number">2</span> |
| <span class="identifier">fn</span><span class="special">():</span> <span class="number">3</span> |
| <span class="identifier">fn</span><span class="special">():</span> <span class="number">4</span> |
| <span class="identifier">fn</span><span class="special">():</span> <span class="number">5</span> |
| <span class="identifier">sink</span> <span class="identifier">is</span> <span class="identifier">complete</span><span class="special">:</span> <span class="keyword">false</span> |
| <span class="special">~</span><span class="identifier">X</span><span class="special">()</span> |
| </pre> |
| <h5> |
| <a name="coroutine.coroutine.asymmetric.h8"></a> |
| <span class="phrase"><a name="coroutine.coroutine.asymmetric.range_iterators"></a></span><a class="link" href="asymmetric.html#coroutine.coroutine.asymmetric.range_iterators">Range |
| iterators</a> |
| </h5> |
| <p> |
| <span class="bold"><strong>Boost.Coroutine</strong></span> provides output- and input-iterators |
| using <span class="bold"><strong>Boost.Range</strong></span>. <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> |
| can be used via input-iterators using <span class="emphasis"><em>std::begin()</em></span> and |
| <span class="emphasis"><em>std::end()</em></span>. |
| </p> |
| <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">number</span><span class="special">=</span><span class="number">2</span><span class="special">,</span><span class="identifier">exponent</span><span class="special">=</span><span class="number">8</span><span class="special">;</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">asymmetric_coroutine</span><span class="special"><</span> <span class="keyword">int</span> <span class="special">>::</span><span class="identifier">pull_type</span> <span class="identifier">source</span><span class="special">(</span> |
| <span class="special">[&](</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">asymmetric_coroutine</span><span class="special"><</span> <span class="keyword">int</span> <span class="special">>::</span><span class="identifier">push_type</span> <span class="special">&</span> <span class="identifier">sink</span><span class="special">){</span> |
| <span class="keyword">int</span> <span class="identifier">counter</span><span class="special">=</span><span class="number">0</span><span class="special">,</span><span class="identifier">result</span><span class="special">=</span><span class="number">1</span><span class="special">;</span> |
| <span class="keyword">while</span><span class="special">(</span><span class="identifier">counter</span><span class="special">++<</span><span class="identifier">exponent</span><span class="special">){</span> |
| <span class="identifier">result</span><span class="special">=</span><span class="identifier">result</span><span class="special">*</span><span class="identifier">number</span><span class="special">;</span> |
| <span class="identifier">sink</span><span class="special">(</span><span class="identifier">result</span><span class="special">);</span> |
| <span class="special">}</span> |
| <span class="special">});</span> |
| |
| <span class="keyword">for</span> <span class="special">(</span><span class="keyword">auto</span> <span class="identifier">i</span><span class="special">:</span><span class="identifier">source</span><span class="special">)</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">i</span> <span class="special"><<</span> <span class="string">" "</span><span class="special">;</span> |
| |
| <span class="identifier">output</span><span class="special">:</span> |
| <span class="number">2</span> <span class="number">4</span> <span class="number">8</span> <span class="number">16</span> <span class="number">32</span> <span class="number">64</span> <span class="number">128</span> <span class="number">256</span> |
| </pre> |
| <p> |
| <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::iterator::operator++()</em></span> |
| corresponds to <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::operator()</em></span>; |
| <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::iterator::operator*()</em></span> |
| roughly corresponds to <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::get()</em></span>. |
| An iterator originally obtained from <span class="emphasis"><em>std::begin()</em></span> of |
| an <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> compares |
| equal to an iterator obtained from <span class="emphasis"><em>std::end()</em></span> of that |
| same <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span> instance |
| when its <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::operator bool</em></span> |
| would return <code class="computeroutput"><span class="keyword">false</span></code>]. |
| </p> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| If <code class="computeroutput"><span class="identifier">T</span></code> is a move-only type, |
| then <span class="emphasis"><em>asymmetric_coroutine<T>::pull_type::iterator</em></span> |
| may only be dereferenced once before it is incremented again. |
| </p></td></tr> |
| </table></div> |
| <p> |
| Output-iterators can be created from <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span>. |
| </p> |
| <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">asymmetric_coroutine</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">push_type</span> <span class="identifier">sink</span><span class="special">(</span> |
| <span class="special">[&](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">coroutines</span><span class="special">::</span><span class="identifier">asymmetric_coroutine</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">pull_type</span><span class="special">&</span> <span class="identifier">source</span><span class="special">){</span> |
| <span class="keyword">while</span><span class="special">(</span><span class="identifier">source</span><span class="special">){</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">source</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special"><<</span> <span class="string">" "</span><span class="special">;</span> |
| <span class="identifier">source</span><span class="special">();</span> |
| <span class="special">}</span> |
| <span class="special">});</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">v</span><span class="special">{</span><span class="number">1</span><span class="special">,</span><span class="number">1</span><span class="special">,</span><span class="number">2</span><span class="special">,</span><span class="number">3</span><span class="special">,</span><span class="number">5</span><span class="special">,</span><span class="number">8</span><span class="special">,</span><span class="number">13</span><span class="special">,</span><span class="number">21</span><span class="special">,</span><span class="number">34</span><span class="special">,</span><span class="number">55</span><span class="special">};</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">copy</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">begin</span><span class="special">(</span><span class="identifier">v</span><span class="special">),</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">end</span><span class="special">(</span><span class="identifier">v</span><span class="special">),</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">begin</span><span class="special">(</span><span class="identifier">sink</span><span class="special">));</span> |
| </pre> |
| <p> |
| <span class="emphasis"><em>asymmetric_coroutine<>::push_type::iterator::operator*()</em></span> |
| roughly corresponds to <span class="emphasis"><em>asymmetric_coroutine<>::push_type::operator()</em></span>. |
| An iterator originally obtained from <span class="emphasis"><em>std::begin()</em></span> of |
| an <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> compares |
| equal to an iterator obtained from <span class="emphasis"><em>std::end()</em></span> of that |
| same <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> instance |
| when its <span class="emphasis"><em>asymmetric_coroutine<>::push_type::operator bool</em></span> |
| would return <code class="computeroutput"><span class="keyword">false</span></code>. |
| </p> |
| <h5> |
| <a name="coroutine.coroutine.asymmetric.h9"></a> |
| <span class="phrase"><a name="coroutine.coroutine.asymmetric.exit_a__emphasis_coroutine_function__emphasis_"></a></span><a class="link" href="asymmetric.html#coroutine.coroutine.asymmetric.exit_a__emphasis_coroutine_function__emphasis_">Exit |
| a <span class="emphasis"><em>coroutine-function</em></span></a> |
| </h5> |
| <p> |
| <span class="emphasis"><em>coroutine-function</em></span> is exited with a simple return statement |
| jumping back to the calling routine. The <span class="emphasis"><em>asymmetric_coroutine<>::pull_type</em></span>, |
| <span class="emphasis"><em>asymmetric_coroutine<>::push_type</em></span> becomes complete, |
| e.g. <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::operator bool</em></span>, |
| <span class="emphasis"><em>asymmetric_coroutine<>::push_type::operator bool</em></span> |
| will return <code class="computeroutput"><span class="keyword">false</span></code>. |
| </p> |
| <div class="important"><table border="0" summary="Important"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../../doc/src/images/important.png"></td> |
| <th align="left">Important</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| After returning from <span class="emphasis"><em>coroutine-function</em></span> the <span class="emphasis"><em>coroutine</em></span> |
| is complete (can not resumed with <span class="emphasis"><em>asymmetric_coroutine<>::push_type::operator()</em></span>, |
| <span class="emphasis"><em>asymmetric_coroutine<>::pull_type::operator()</em></span>). |
| </p></td></tr> |
| </table></div> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2009 Oliver Kowalke<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) |
| </p> |
| </div></td> |
| </tr></table> |
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