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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>wait</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_010_428"> </a>NAME</h4><blockquote>wait, waitpid - wait for a child process to stop or terminate</blockquote><h4><a name = "tag_000_010_429"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="systypes.h.html">sys/types.h</a>>#include <<a href="syswait.h.html">sys/wait.h</a>>pid_t wait(int *<i>stat_loc</i>);pid_t waitpid(pid_t <i>pid</i>, int *<i>stat_loc</i>, int <i>options</i>);</code></pre></blockquote><h4><a name = "tag_000_010_430"> </a>DESCRIPTION</h4><blockquote>The<i>wait()</i>and<i><a href="waitpid.html">waitpid()</a></i>functions allow the calling process to obtain status informationpertaining to one of its child processes.Various options permit status information to be obtained forchild processes that have terminated or stopped.If status information is available for two or more childprocesses, the order in which their status is reported isunspecified.<p>The<i>wait()</i>function will suspend execution of the calling thread untilstatus information for one of its terminated child processes isavailable, or until delivery of a signal whose action is eitherto execute a signal-catching function or to terminate theprocess.If more than one thread is suspended in<i>wait()</i>or<i><a href="waitpid.html">waitpid()</a></i>awaiting termination of the same process, exactly one thread willreturn the process status at the time of the target processtermination.If status information is available prior to the call to<i>wait()</i>,return will be immediate.<p>The<i><a href="waitpid.html">waitpid()</a></i>function will behave identically to<i>wait()</i>,if the<i>pid</i>argument is (<b>pid_t</b>)-1 and the<i>options</i>argument is 0. Otherwise, its behaviour will be modified by the values of the<i>pid</i>and<i>options</i>arguments.<p>The<i>pid</i>argument specifies a set of child processes for which status isrequested.The<i><a href="waitpid.html">waitpid()</a></i>function will only return the status of a child process from this set:<p><ul><p><li>If<i>pid</i>is equal to (<b>pid_t</b>)-1, status is requested for anychild process.In this respect,<i><a href="waitpid.html">waitpid()</a></i>is then equivalent to<i>wait()</i>.<p><li>If<i>pid</i>is greater than 0, it specifies the process ID of a singlechild process for which status is requested.<p><li>If<i>pid</i>is 0, status is requested for any child process whoseprocess group ID is equal to that of the calling process.<p><li>If<i>pid</i>is less than (<b>pid_t</b>)-1, status is requested for any child process whoseprocess group ID is equal to the absolute value of<i>pid</i>.<p></ul><p>The<i>options</i>argument is constructed from the bitwise-inclusive OR of zero ormore of the following flags, defined in the header<i><a href="syswait.h.html"><sys/wait.h></a></i>.<dl compact><dt>WCONTINUED<dd>The<i><a href="waitpid.html">waitpid()</a></i>function will report the status of any continued child process specified by<i>pid</i> whose status has not been reported since it continued from a jobcontrol stop.<dt>WNOHANG<dd>The<i><a href="waitpid.html">waitpid()</a></i>function will not suspend execution of the calling thread if status is not immediately available for one of the childprocesses specified by<i>pid</i>.<dt>WUNTRACED<dd>The status of anychild processes specified by<i>pid</i>that are stopped, and whose status has not yet been reportedsince they stopped, will also be reported to the requestingprocess.</dl><p>If the calling process has SA_NOCLDWAIT set or has SIGCHLD set to SIG_IGN,and the process has no unwaited for children that were transformedinto zombie processes, the calling thread will block until all of the children of the processcontaining the calling thread terminate, and<i>wait()</i>and<i><a href="waitpid.html">waitpid()</a></i>will fail and set<i>errno</i>to [ECHILD].<p>If<i>wait()</i>or<i><a href="waitpid.html">waitpid()</a></i>return because the status of a child process is available, thesefunctions will return a value equal to the process ID of thechild process.In this case, if the value of the argument<i>stat_loc</i>is not a null pointer, information will be stored in the location pointedto by<i>stat_loc</i>.If and only if the status returned is from a terminated childprocess that returned 0 from<i>main()</i>or passed 0 as the<i>status</i>argument to<i><a href="_exit.html">_exit()</a></i>or<i><a href="exit.html">exit()</a></i>,the value stored at the location pointed to by<i>stat_loc</i>will be 0.Regardless of its value, this information may be interpretedusing the following macros, which are defined in<i><a href="syswait.h.html"><sys/wait.h></a></i>and evaluate to integral expressions; the<i>stat_val</i>argument is the integer value pointed to by<i>stat_loc.</i><dl compact><dt>WIFEXITED(<i>stat_val</i>)<dd>Evaluates to a non-zero value if status was returned for a childprocess that terminated normally.<dt>WEXITSTATUS(<i>stat_val</i>)<dd>If the value of WIFEXITED(<i>stat_val</i>) is non-zero, this macroevaluates to the low-order 8 bits of the<i>status</i>argument that the child process passed to<i><a href="_exit.html">_exit()</a></i>or<i><a href="exit.html">exit()</a></i>,or the value the child process returned from<i>main()</i>.<dt>WIFSIGNALED(<i>stat_val</i>)<dd>Evaluates to non-zero value if status was returned for a childprocess that terminated due to the receipt of a signal that wasnot caught (see<i><a href="signal.h.html"><signal.h></a></i>).<dt>WTERMSIG(<i>stat_val</i>)<dd>If the value of WIFSIGNALED(<i>stat_val</i>) is non-zero, this macroevaluates to the number of the signal that caused the terminationof the child process.<dt>WIFSTOPPED(<i>stat_val</i>)<dd>Evaluates to a non-zero value if status was returned for a childprocess that is currently stopped.<dt>WSTOPSIG(<i>stat_val</i>)<dd>If the value of WIFSTOPPED(<i>stat_val</i>) is non-zero, this macroevaluates to the number of the signal that caused the childprocess to stop.<dt>WIFCONTINUED(<i>stat_val</i>)<dd>Evaluates to a non-zero value if status was returned for achild process that has continued from a job control stop.</dl><p>If the information pointed to by <i>stat_loc</i> was stored by a call to<i><a href="waitpid.html">waitpid()</a></i>that specified the WUNTRACED flag and did not specify the WCONTINUED flag,exactly one of the macros WIFEXITED(*<i>stat_loc</i>),WIFSIGNALED(*<i>stat_loc</i>), and WIFSTOPPED(*<i>stat_loc</i>), will evaluateto a non-zero value.<p>If the information pointed to by <i>stat_loc</i> was stored by a call to<i><a href="waitpid.html">waitpid()</a></i>that specified the WUNTRACED and WCONTINUEDflags, exactly one of the macrosWIFEXITED(*<i>stat_loc</i>), WIFSIGNALED(*<i>stat_loc</i>),WIFSTOPPED(*<i>stat_loc</i>), and WIFCONTINUED(*<i>stat_loc</i>),will evaluate to a non-zero value.<p>If the information pointed to by <i>stat_loc</i> was stored by a call to<i><a href="waitpid.html">waitpid()</a></i>that did not specify the WUNTRACED or WCONTINUEDflags, or by a call to the<i>wait()</i>function, exactly one of the macros WIFEXITED(*<i>stat_loc</i>)and WIFSIGNALED(*<i>stat_loc</i>) will evaluate to a non-zero value.<p>If the information pointed to by <i>stat_loc</i> was stored by a call to<i><a href="waitpid.html">waitpid()</a></i>that did not specify the WUNTRACED flag and specified the WCONTINUED flag,or by a call to the<i>wait()</i>function, exactly one of the macrosWIFEXITED(*<i>stat_loc</i>), WIFSIGNALED(*<i>stat_loc</i>), and WIFCONTINUED(*<i>stat_loc</i>),will evaluate to a non-zero value.<p>There may be additional implementation-dependent circumstances under which<i>wait()</i>or<i><a href="waitpid.html">waitpid()</a></i>report status.This will not occur unless the calling process or one of itschild processes explicitly makes use of a non-standard extension.In these cases the interpretation of the reported status isimplementation-dependent.<p>If a parent process terminates without waiting for all of itschild processes to terminate, the remaining child processes willbe assigned a new parent process ID corresponding to animplementation-dependent system process.<br></blockquote><h4><a name = "tag_000_010_431"> </a>RETURN VALUE</h4><blockquote>If<i>wait()</i>or<i><a href="waitpid.html">waitpid()</a></i>returns because the status of a child process isavailable, these functions will return a value equal to theprocess ID of the child process for which status is reported.If<i>wait()</i>or<i><a href="waitpid.html">waitpid()</a></i>returns due to the delivery of a signal to the callingprocess, -1 will be returned and<i>errno</i>will be set to [EINTR]. If<i><a href="waitpid.html">waitpid()</a></i>was invoked with WNOHANG set in<i>options</i>,it has at least one child process specified by<i>pid</i>for which status is not available, and status is not availablefor any process specified by<i>pid</i>,0 will be returned. Otherwise, (<b>pid_t</b>)-1 will be returned, and<i>errno</i>will be set to indicate the error.<br></blockquote><h4><a name = "tag_000_010_432"> </a>ERRORS</h4><blockquote>The<i>wait()</i>function will fail if:<dl compact><dt>[ECHILD]<dd>The calling process has no existing unwaited-for childprocesses.<dt>[EINTR]<dd>The function was interrupted by a signal.The value of the location pointed to by<i>stat_loc</i>is undefined.</dl><p>The<i><a href="waitpid.html">waitpid()</a></i>function will fail if:<dl compact><dt>[ECHILD]<dd>The process or process group specified by<i>pid</i>does not exist or is not a child of the calling process.<dt>[EINTR]<dd>The function was interrupted by a signal.The value of the location pointed to by<i>stat_loc</i>is undefined.<dt>[EINVAL]<dd>The<i>options</i>argument is not valid.</dl></blockquote><h4><a name = "tag_000_010_433"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_010_434"> </a>APPLICATION USAGE</h4><blockquote>None.</blockquote><h4><a name = "tag_000_010_435"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_010_436"> </a>SEE ALSO</h4><blockquote><i><a href="exec.html">exec</a></i>,<i><a href="exit.html">exit()</a></i>,<i><a href="fork.html">fork()</a></i>,<i><a href="wait3.html">wait3()</a></i>,<i><a href="waitid.html">waitid()</a></i>,<i><a href="systypes.h.html"><sys/types.h></a></i>,<i><a href="syswait.h.html"><sys/wait.h></a></i>.</blockquote><h4>DERIVATION</h4><blockquote>Derived from Issue 1 of the SVID.</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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