xsh_chap02_09.html

posix标准英文,html格式

<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/stat.html"><i>stat</i>()</a><br>
<a href="../functions/strerror.html"><i>strerror</i>()</a><br>
<a href="../functions/strerror_r.html"><i>strerror_r</i>()</a><br>
<a href="../functions/strftime.html"><i>strftime</i>()</a><br>
<a href="../functions/symlink.html"><i>symlink</i>()</a><br>
<a href="../functions/sync.html"><i>sync</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/tzset.html"><i>tzset</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/wcsftime.html"><i>wcsftime</i>()</a><br>
<a href="../functions/wordexp.html"><i>wordexp</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, or when a thread calls <a href=
"../functions/pthread_exit.html"><i>pthread_exit</i>()</a>, the thread first disables cancellation by setting its cancelability
state to PTHREAD_CANCEL_DISABLE and its cancelability type to PTHREAD_CANCEL_DEFERRED. The cancelability state shall remain set to
PTHREAD_CANCEL_DISABLE until the thread has terminated. The behavior is undefined if a cancellation cleanup handler or
thread-specific data destructor routine changes the cancelability state to PTHREAD_CANCEL_ENABLE.</p>

<p>The routines in the thread's list of cancellation cleanup handlers 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). 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-specific data
destructors (if any) associated with thread-specific data keys for which the thread has non-NULL values will be run, in unspecified
order, as described for <a href="../functions/pthread_key_create.html"><i>pthread_key_create</i>()</a>.</p>

<p>After all cancellation cleanup handlers and thread-specific data destructors have returned, thread execution is terminated. If
the thread has terminated because of a call to <a href="../functions/pthread_exit.html"><i>pthread_exit</i>()</a>, the
<i>value_ptr</i> argument is made available to any threads joining with the target. If the thread has terminated by acting on a
cancellation request, 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>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">  2.9.6 </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">  2.9.7 </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>

<h4><a name="tag_02_09_08">  2.9.8 </a>Use of Application-Managed Thread Stacks</h4>

<p>An ``application-managed thread stack'' is a region of memory allocated by the application-for example, memory returned by the
<a href="../functions/malloc.html"><i>malloc</i>()</a> or <a href="../functions/mmap.html"><i>mmap</i>()</a> functions-and
designated as a stack through the act of passing an address related to that memory as the <i>stackaddr</i> argument to <a href=
"../functions/pthread_attr_setstackaddr.html"><i>pthread_attr_setstackaddr</i>()</a> (obsolete) or by passing the address and size
of the stack, respectively, as the <i>stackaddr</i> and <i>stacksize</i> arguments to <a href=
"../functions/pthread_attr_setstack.html"><i>pthread_attr_setstack</i>()</a>. Application-managed stacks allow the application to
precisely control the placement and size of a stack.</p>

<p>The application grants to the implementation permanent ownership of and control over the application-managed stack when the
attributes object in which the <i>stack</i> or <i>stackaddr</i> attribute has been set is used, either by presenting that
attribute's object as the <i>attr</i> argument in a call to <a href="../functions/pthread_create.html"><i>pthread_create</i>()</a>
that completes successfully, or by storing a pointer to the attributes object in the <i>sigev_notify_attributes</i> member of a
<b>struct sigevent</b> and passing that <b>struct sigevent</b> to a function accepting such argument that completes successfully.
The application may thereafter utilize the memory within the stack only within the normal context of stack usage within or properly
synchronized with a thread that has been scheduled by the implementation with stack pointer value(s) that are within the range of
that stack. In particular, the region of memory cannot be freed, nor can it be later specified as the stack for another thread.</p>

<p>When specifying an attributes object with an application-managed stack through the <i>sigev_notify_attributes</i> member of a
<b>struct sigevent</b>, the results are undefined if the requested signal is generated multiple times (as for a repeating
timer).</p>

<p>Until an attributes object in which the <i>stack</i> or <i>stackaddr</i> attribute has been set is used, the application retains
ownership of and control over the memory allocated to the stack. It may free or reuse the memory as long as it either deletes the
attributes object, or before using the attributes object replaces the stack by making an additional call to the same function,
either <a href="../functions/pthread_attr_setstackaddr.html"><i>pthread_attr_setstackaddr</i>()</a> or <a href=
"../functions/pthread_attr_setstack.html"><i>pthread_attr_setstack</i>()</a>, that was used originally to designate the stack.
There is no mechanism to retract the reference to an application-managed stack by an existing attributes object.</p>

<p>Once an attributes object with an application-managed stack has been used, that attributes object cannot be used again by a
subsequent call to <a href="../functions/pthread_create.html"><i>pthread_create</i>()</a> or any function accepting a <b>struct
sigevent</b> with <i>sigev_notify_attributes</i> containing a pointer to the attributes object, without designating an unused
application-managed stack by making an additional call to the function originally used to define the stack, <a href=
"../functions/pthread_attr_setstack.html"><i>pthread_attr_setstack</i>()</a> or <a href=
"../functions/pthread_attr_setstackaddr.html"><i>pthread_attr_setstackaddr</i>()</a>.</p>

<hr>
<h4><a name="tag_02_09_09"></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_4">4.</a></dt>

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

<dt><a name="tag_foot_4">4.</a></dt>

<dd>If <i>opterr</i> is non-zero.</dd>
</dl>




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