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| <h2 class="chapter">10 Reentrancy</h2> |
| |
| <p><a name="index-reentrancy-449"></a>Reentrancy is a characteristic of library functions which allows multiple |
| processes to use the same address space with assurance that the values stored |
| in those spaces will remain constant between calls. The Red Hat |
| newlib implementation of the library functions ensures that |
| whenever possible, these library functions are reentrant. However, |
| there are some functions that can not be trivially made reentrant. |
| Hooks have been provided to allow you to use these functions in a fully |
| reentrant fashion. |
| |
| <p><a name="index-g_t_005freent-450"></a><a name="index-reent_002eh-451"></a><a name="index-reentrancy-structure-452"></a>These hooks use the structure <code>_reent</code> defined in <samp><span class="file">reent.h</span></samp>. |
| A variable defined as ‘<samp><span class="samp">struct _reent</span></samp>’ is called a <dfn>reentrancy |
| structure</dfn>. All functions which must manipulate global information are |
| available in two versions. The first version has the usual name, and |
| uses a single global instance of the reentrancy structure. The second |
| has a different name, normally formed by prepending ‘<samp><span class="samp">_</span></samp>’ and |
| appending ‘<samp><span class="samp">_r</span></samp>’, and takes a pointer to the particular reentrancy |
| structure to use. |
| |
| <p>For example, the function <code>fopen</code> takes two arguments, <var>file</var> |
| and <var>mode</var>, and uses the global reentrancy structure. The function |
| <code>_fopen_r</code> takes the arguments, <var>struct_reent</var>, which is a |
| pointer to an instance of the reentrancy structure, <var>file</var> |
| and <var>mode</var>. |
| |
| <p>There are two versions of ‘<samp><span class="samp">struct _reent</span></samp>’, a normal one and one |
| for small memory systems, controlled by the <code>_REENT_SMALL</code> |
| definition from the (automatically included) <samp><span class="file"><sys/config.h></span></samp>. |
| |
| <p><a name="index-global-reentrancy-structure-453"></a><a name="index-g_t_005fimpure_005fptr-454"></a>Each function which uses the global reentrancy structure uses the global |
| variable <code>_impure_ptr</code>, which points to a reentrancy structure. |
| |
| <p>This means that you have two ways to achieve reentrancy. Both require |
| that each thread of execution control initialize a unique global |
| variable of type ‘<samp><span class="samp">struct _reent</span></samp>’: |
| |
| <ol type=1 start=1> |
| <li><a name="index-extra-argument_002c-reentrant-fns-455"></a>Use the reentrant versions of the library functions, after initializing |
| a global reentrancy structure for each process. Use the pointer to this |
| structure as the extra argument for all library functions. |
| |
| <li>Ensure that each thread of execution control has a pointer to its own |
| unique reentrancy structure in the global variable <code>_impure_ptr</code>, |
| and call the standard library subroutines. |
| </ol> |
| |
| <p><a name="index-list-of-reentrant-functions-456"></a><a name="index-reentrant-function-list-457"></a>The following functions are provided in both reentrant |
| and non-reentrant versions. |
| |
| <pre class="example"><br><em>Equivalent for errno variable:</em><br> |
| _errno_r |
| |
| <br><em>Locale functions:</em><br> |
| _localeconv_r _setlocale_r |
| |
| <br><em>Equivalents for stdio variables:</em><br> |
| _stdin_r _stdout_r _stderr_r |
| |
| |
| <br><em>Stdio functions:</em><br> |
| _fdopen_r _perror_r _tempnam_r |
| _fopen_r _putchar_r _tmpnam_r |
| _getchar_r _puts_r _tmpfile_r |
| _gets_r _remove_r _vfprintf_r |
| _iprintf_r _rename_r _vsnprintf_r |
| _mkstemp_r _snprintf_r _vsprintf_r |
| _mktemp_t _sprintf_r |
| |
| <br><em>Signal functions:</em><br> |
| _init_signal_r _signal_r |
| _kill_r __sigtramp_r |
| _raise_r |
| |
| <br><em>Stdlib functions:</em><br> |
| _calloc_r _mblen_r _setenv_r |
| _dtoa_r _mbstowcs_r _srand_r |
| _free_r _mbtowc_r _strtod_r |
| _getenv_r _memalign_r _strtol_r |
| _mallinfo_r _mstats_r _strtoul_r |
| _malloc_r _putenv_r _system_r |
| _malloc_r _rand_r _wcstombs_r |
| _malloc_stats_r _realloc_r _wctomb_r |
| |
| <br><em>String functions:</em><br> |
| _strdup_r _strtok_r |
| |
| <br><em>System functions:</em><br> |
| _close_r _link_r _unlink_r |
| _execve_r _lseek_r _wait_r |
| _fcntl_r _open_r _write_r |
| _fork_r _read_r |
| _fstat_r _sbrk_r |
| _gettimeofday_r _stat_r |
| _getpid_r _times_r |
| |
| |
| <br><em>Time function:</em><br> |
| _asctime_r |
| </pre> |
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