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| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="log.rationale"></a><a class="link" href="rationale.html" title="Rationale and FAQ">Rationale and FAQ</a> |
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| <dt><span class="section"><a href="rationale.html#log.rationale.why_str_lit">Why string literals as scope |
| names?</a></span></dt> |
| <dt><span class="section"><a href="rationale/why_weak_scoped_attributes.html">Why scoped |
| attributes don't override existing attributes?</a></span></dt> |
| <dt><span class="section"><a href="rationale/why_weak_record_ordering.html">Why log records |
| are weakly ordered in a multithreaded application?</a></span></dt> |
| <dt><span class="section"><a href="rationale/why_attribute_manips_dont_affect_filters.html">Why |
| attributes set with stream manipulators do not participate in filtering?</a></span></dt> |
| <dt><span class="section"><a href="rationale/why_not_lazy_streaming.html">Why not using lazy |
| streaming?</a></span></dt> |
| <dt><span class="section"><a href="rationale/why_not_log4j.html">Why not using hierarchy |
| of loggers, like in log4j? Why not Boost.Log4j? Etc.</a></span></dt> |
| <dt><span class="section"><a href="rationale/fork_support.html">Does Boost.Log support process |
| forking?</a></span></dt> |
| <dt><span class="section"><a href="rationale/init_term_support.html">Does Boost.Log support |
| logging at process initialization and termination?</a></span></dt> |
| <dt><span class="section"><a href="rationale/why_crash_on_term.html">Why my application crashes |
| on process termination when file sinks are used?</a></span></dt> |
| <dt><span class="section"><a href="rationale/namespace_mangling.html">Why my application |
| fails to link with Boost.Log? What's the fuss about library namespaces?</a></span></dt> |
| <dt><span class="section"><a href="rationale/msvc_link_fails_lnk1123.html">Why MSVC 2010 |
| fails to link the library with error LNK1123: failure during conversion to |
| COFF: file invalid or corrupt?</a></span></dt> |
| </dl></div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="log.rationale.why_str_lit"></a><a class="link" href="rationale.html#log.rationale.why_str_lit" title="Why string literals as scope names?">Why string literals as scope |
| names?</a> |
| </h3></div></div></div> |
| <p> |
| One may wonder why not allow arbitrary strings to be used as named scope |
| names. The answer is simple: for performance and safety reasons. Named scope |
| support functionality has one significant difference from other attribute-related |
| features of the library. The scope stack is maintained even when no logging |
| is done, so if a function <code class="computeroutput"><span class="identifier">foo</span></code> |
| has a <code class="computeroutput"><span class="identifier">BOOST_LOG_FUNCTION</span><span class="special">()</span></code> statement in its body, it is always a slowdown. |
| Allowing the scope name to be an arbitrary string would make the slowdown |
| significantly greater because of the need to allocate memory and copy the |
| string (not to mention that there would be a need to previously format it, |
| which also takes its toll). |
| </p> |
| <p> |
| Dynamic memory allocation also introduces exception safety issues: the <code class="computeroutput"><span class="identifier">BOOST_LOG_FUNCTION</span><span class="special">()</span></code> |
| statement (and alikes) would become a potential source of exceptions. These |
| issues would complicate user's code if he wants to solve memory allocation |
| problems gracefully. |
| </p> |
| <p> |
| One possible alternative solution would be pooling pre-formatted and pre-allocated |
| scope names somewhere but this would surely degrade performance even more |
| and introduce the problem of detecting when to update or free pooled strings. |
| </p> |
| <p> |
| Therefore restricting to string literals seemed to be the optimal decision, |
| which reduced dynamic memory usage and provided enough flexibility for common |
| needs. |
| </p> |
| </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 © 2007-2015 Andrey |
| Semashev<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>). |
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