xsh_chap02_09.html

IEEE 1003.1-2003, Single Unix Specification v3

<a href="../functions/pclose.html"><i>pclose</i>()</a><br>
<a href="../functions/perror.html"><i>perror</i>()</a><br>
<a href="../functions/popen.html"><i>popen</i>()</a><br>
<a href="../functions/posix_fadvise.html"><i>posix_fadvise</i>()</a><br>
<a href="../functions/posix_fallocate.html"><i>posix_fallocate</i>()</a><br>
<a href="../functions/posix_madvise.html"><i>posix_madvise</i>()</a><br>
<a href="../functions/posix_spawn.html"><i>posix_spawn</i>()</a><br>
<a href="../functions/posix_spawnp.html"><i>posix_spawnp</i>()</a><br>
<a href="../functions/posix_trace_clear.html"><i>posix_trace_clear</i>()</a><br>
<a href="../functions/posix_trace_close.html"><i>posix_trace_close</i>()</a><br>
<a href="../functions/posix_trace_create.html"><i>posix_trace_create</i>()</a><br>
<a href="../functions/posix_trace_create_withlog.html"><i>posix_trace_create_withlog</i>()</a><br>
<a href="../functions/posix_trace_eventtypelist_getnext_id.html"><i>posix_trace_eventtypelist_getnext_id</i>()</a><br>
<a href="../functions/posix_trace_eventtypelist_rewind.html"><i>posix_trace_eventtypelist_rewind</i>()</a><br>
<a href="../functions/posix_trace_flush.html"><i>posix_trace_flush</i>()</a><br>
<a href="../functions/posix_trace_get_attr.html"><i>posix_trace_get_attr</i>()</a><br>
<a href="../functions/posix_trace_get_filter.html"><i>posix_trace_get_filter</i>()</a><br>
<a href="../functions/posix_trace_get_status.html"><i>posix_trace_get_status</i>()</a><br>
<a href="../functions/posix_trace_getnext_event.html"><i>posix_trace_getnext_event</i>()</a><br>
<a href="../functions/posix_trace_open.html"><i>posix_trace_open</i>()</a><br>
<a href="../functions/posix_trace_rewind.html"><i>posix_trace_rewind</i>()</a><br>
<a href="../functions/posix_trace_set_filter.html"><i>posix_trace_set_filter</i>()</a><br>
<a href="../functions/posix_trace_shutdown.html"><i>posix_trace_shutdown</i>()</a><br>
<a href="../functions/posix_trace_timedgetnext_event.html"><i>posix_trace_timedgetnext_event</i>()</a><br>
<a href="../functions/posix_typed_mem_open.html"><i>posix_typed_mem_open</i>()</a><br>
<a href="../functions/printf.html"><i>printf</i>()</a><br>
<a href="../functions/pthread_rwlock_rdlock.html"><i>pthread_rwlock_rdlock</i>()</a><br>
<a href="../functions/pthread_rwlock_timedrdlock.html"><i>pthread_rwlock_timedrdlock</i>()</a><br>
<a href="../functions/pthread_rwlock_timedwrlock.html"><i>pthread_rwlock_timedwrlock</i>()</a><br>
&nbsp;</p>
</td>
<td align="left">
<p class="tent"><br>
<a href="../functions/pthread_rwlock_wrlock.html"><i>pthread_rwlock_wrlock</i>()</a><br>
<a href="../functions/putc.html"><i>putc</i>()</a><br>
<a href="../functions/putc_unlocked.html"><i>putc_unlocked</i>()</a><br>
<a href="../functions/putchar.html"><i>putchar</i>()</a><br>
<a href="../functions/putchar_unlocked.html"><i>putchar_unlocked</i>()</a><br>
<a href="../functions/puts.html"><i>puts</i>()</a><br>
<a href="../functions/pututxline.html"><i>pututxline</i>()</a><br>
<a href="../functions/putwc.html"><i>putwc</i>()</a><br>
<a href="../functions/putwchar.html"><i>putwchar</i>()</a><br>
<a href="../functions/readdir.html"><i>readdir</i>()</a><br>
<a href="../functions/readdir_r.html"><i>readdir_r</i>()</a><br>
<a href="../functions/remove.html"><i>remove</i>()</a><br>
<a href="../functions/rename.html"><i>rename</i>()</a><br>
<a href="../functions/rewind.html"><i>rewind</i>()</a><br>
<a href="../functions/rewinddir.html"><i>rewinddir</i>()</a><br>
<a href="../functions/scanf.html"><i>scanf</i>()</a><br>
<a href="../functions/seekdir.html"><i>seekdir</i>()</a><br>
<a href="../functions/semop.html"><i>semop</i>()</a><br>
<a href="../functions/setgrent.html"><i>setgrent</i>()</a><br>
<a href="../functions/sethostent.html"><i>sethostent</i>()</a><br>
<a href="../functions/setnetent.html"><i>setnetent</i>()</a><br>
<a href="../functions/setprotoent.html"><i>setprotoent</i>()</a><br>
<a href="../functions/setpwent.html"><i>setpwent</i>()</a><br>
<a href="../functions/setservent.html"><i>setservent</i>()</a><br>
<a href="../functions/setutxent.html"><i>setutxent</i>()</a><br>
<a href="../functions/strerror.html"><i>strerror</i>()</a><br>
<a href="../functions/syslog.html"><i>syslog</i>()</a><br>
<a href="../functions/tmpfile.html"><i>tmpfile</i>()</a><br>
<a href="../functions/tmpnam.html"><i>tmpnam</i>()</a><br>
<a href="../functions/ttyname.html"><i>ttyname</i>()</a><br>
<a href="../functions/ttyname_r.html"><i>ttyname_r</i>()</a><br>
<a href="../functions/ungetc.html"><i>ungetc</i>()</a><br>
<a href="../functions/ungetwc.html"><i>ungetwc</i>()</a><br>
<a href="../functions/unlink.html"><i>unlink</i>()</a><br>
<a href="../functions/vfprintf.html"><i>vfprintf</i>()</a><br>
<a href="../functions/vfwprintf.html"><i>vfwprintf</i>()</a><br>
<a href="../functions/vprintf.html"><i>vprintf</i>()</a><br>
<a href="../functions/vwprintf.html"><i>vwprintf</i>()</a><br>
<a href="../functions/wprintf.html"><i>wprintf</i>()</a><br>
<a href="../functions/wscanf.html"><i>wscanf</i>()</a><br>
&nbsp;</p>
</td>
</tr>
</table>

<p>An implementation shall not introduce cancellation points into any other functions specified in this volume of
IEEE&nbsp;Std&nbsp;1003.1-2001.</p>

<p>The side effects of acting upon a cancellation request while suspended during a call of a function are the same as the side
effects that may be seen in a single-threaded program when a call to a function is interrupted by a signal and the given function
returns [EINTR]. Any such side effects occur before any cancellation cleanup handlers are called.</p>

<p>Whenever a thread has cancelability enabled and a cancellation request has been made with that thread as the target, and the
thread then calls any function that is a cancellation point (such as <a href=
"../functions/pthread_testcancel.html"><i>pthread_testcancel</i>()</a> or <a href="../functions/read.html"><i>read</i>()</a>), the
cancellation request shall be acted upon before the function returns. If a thread has cancelability enabled and a cancellation
request is made with the thread as a target while the thread is suspended at a cancellation point, the thread shall be awakened and
the cancellation request shall be acted upon. However, if the thread is suspended at a cancellation point and the event for which
it is waiting occurs before the cancellation request is acted upon, it is unspecified whether the cancellation request is acted
upon or whether the cancellation request remains pending and the thread resumes normal execution.</p>

<h5><a name="tag_02_09_05_03"></a>Thread Cancellation Cleanup Handlers</h5>

<p>Each thread maintains a list of cancellation cleanup handlers. The programmer uses the <a href=
"../functions/pthread_cleanup_push.html"><i>pthread_cleanup_push</i>()</a> and <a href=
"../functions/pthread_cleanup_pop.html"><i>pthread_cleanup_pop</i>()</a> functions to place routines on and remove routines from
this list.</p>

<p>When a cancellation request is acted upon, the routines in the list are invoked one by one in LIFO sequence; that is, the last
routine pushed onto the list (Last In) is the first to be invoked (First Out). The thread invokes the cancellation cleanup handler
with cancellation disabled until the last cancellation cleanup handler returns. When the cancellation cleanup handler for a scope
is invoked, the storage for that scope remains valid. If the last cancellation cleanup handler returns, thread execution is
terminated and a status of PTHREAD_CANCELED is made available to any threads joining with the target. The symbolic constant
PTHREAD_CANCELED expands to a constant expression of type ( <b>void *</b>) whose value matches no pointer to an object in memory
nor the value NULL.</p>

<p>The cancellation cleanup handlers are also invoked when the thread calls <a href=
"../functions/pthread_exit.html"><i>pthread_exit</i>()</a>.</p>

<p>A side effect of acting upon a cancellation request while in a condition variable wait is that the mutex is re-acquired before
calling the first cancellation cleanup handler. In addition, the thread is no longer considered to be waiting for the condition and
the thread shall not have consumed any pending condition signals on the condition.</p>

<p>A cancellation cleanup handler cannot exit via <a href="../functions/longjmp.html"><i>longjmp</i>()</a> or <a href=
"../functions/siglongjmp.html"><i>siglongjmp</i>()</a>.</p>

<h5><a name="tag_02_09_05_04"></a>Async-Cancel Safety</h5>

<p>The <a href="../functions/pthread_cancel.html"><i>pthread_cancel</i>()</a>, <a href=
"../functions/pthread_setcancelstate.html"><i>pthread_setcancelstate</i>()</a>, and <a href=
"../functions/pthread_setcanceltype.html"><i>pthread_setcanceltype</i>()</a> functions are defined to be async-cancel safe.</p>

<p>No other functions in this volume of IEEE&nbsp;Std&nbsp;1003.1-2001 are required to be async-cancel-safe.</p>

<h4><a name="tag_02_09_06"></a>Thread Read-Write Locks</h4>

<p>Multiple readers, single writer (read-write) locks allow many threads to have simultaneous read-only access to data while
allowing only one thread to have exclusive write access at any given time. They are typically used to protect data that is read
more frequently than it is changed.</p>

<p>One or more readers acquire read access to the resource by performing a read lock operation on the associated read-write lock. A
writer acquires exclusive write access by performing a write lock operation. Basically, all readers exclude any writers and a
writer excludes all readers and any other writers.</p>

<p>A thread that has blocked on a read-write lock (for example, has not yet returned from a <a href=
"../functions/pthread_rwlock_rdlock.html"><i>pthread_rwlock_rdlock</i>()</a> or <a href=
"../functions/pthread_rwlock_wrlock.html"><i>pthread_rwlock_wrlock</i>()</a> call) shall not prevent any unblocked thread that is
eligible to use the same processing resources from eventually making forward progress in its execution. Eligibility for processing
resources shall be determined by the scheduling policy.</p>

<p>Read-write locks can be used to synchronize threads in the current process and other processes if they are allocated in memory
that is writable and shared among the cooperating processes and have been initialized for this behavior.</p>

<h4><a name="tag_02_09_07"></a>Thread Interactions with Regular File Operations</h4>

<p>All of the functions <a href="../functions/chmod.html"><i>chmod</i>()</a>, <a href="../functions/close.html"><i>close</i>()</a>,
<a href="../functions/fchmod.html"><i>fchmod</i>()</a>, <a href="../functions/fcntl.html"><i>fcntl</i>()</a>, <a href=
"../functions/fstat.html"><i>fstat</i>()</a>, <a href="../functions/ftruncate.html"><i>ftruncate</i>()</a>, <a href=
"../functions/lseek.html"><i>lseek</i>()</a>, <a href="../functions/open.html"><i>open</i>()</a>, <a href=
"../functions/read.html"><i>read</i>()</a>, <a href="../functions/readlink.html"><i>readlink</i>()</a>, <a href=
"../functions/stat.html"><i>stat</i>()</a>, <a href="../functions/symlink.html"><i>symlink</i>()</a>, and <a href=
"../functions/write.html"><i>write</i>()</a> shall be atomic with respect to each other in the effects specified in
IEEE&nbsp;Std&nbsp;1003.1-2001 when they operate on regular files. If two threads each call one of these functions, each call shall
either see all of the specified effects of the other call, or none of them.</p>

<hr>
<h4><a name="tag_02_09_08"></a>Footnotes</h4>

<dl compact>
<dt><a name="tag_foot_1">1.</a></dt>

<dd>The functions in the table are not shaded to denote applicable options. Individual reference pages should be consulted.</dd>

<dt><a name="tag_foot_2">2.</a></dt>

<dd>When the <i>cmd</i> argument is F_SETLKW.</dd>

<dt><a name="tag_foot_3">3.</a></dt>

<dd>For any value of the <i>cmd</i> argument.</dd>
</dl>




<hr size="2" noshade>
<center><font size="2"><!--footer start-->
UNIX &reg; is a registered Trademark of The Open Group.<br>
POSIX &reg; is a registered Trademark of The IEEE.<br>
[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
]</font></center>

<!--footer end-->
<hr size="2" noshade>
</body>
</html>