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If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner] .TH SIGNAL.H 3HEAD "Feb 5, 2008" .SH NAME signal.h, signal \- base signals .SH SYNOPSIS .LP .nf \fB#include \fR .fi .SH DESCRIPTION .sp .LP A signal is an asynchronous notification of an event. A signal is said to be generated for (or sent to) a process when the event associated with that signal first occurs. Examples of such events include hardware faults, timer expiration and terminal activity, as well as the invocation of the \fBkill\fR(2) or \fBsigsend\fR(2) functions. In some circumstances, the same event generates signals for multiple processes. A process may request a detailed notification of the source of the signal and the reason why it was generated. See \fBsiginfo.h\fR(3HEAD). .sp .LP Signals can be generated synchronously or asynchronously. Events directly caused by the execution of code by a thread, such as a reference to an unmapped, protected, or bad memory can generate \fBSIGSEGV\fR or \fBSIGBUS\fR; a floating point exception can generate \fBSIGFPE\fR; and the execution of an illegal instruction can generate \fBSIGILL\fR. Such events are referred to as traps; signals generated by traps are said to be synchronously generated. Synchronously generated signals are initiated by a specific thread and are delivered to and handled by that thread. .sp .LP Signals may also be generated by calling \fBkill()\fR, \fBsigqueue()\fR, or \fBsigsend()\fR. Events such as keyboard interrupts generate signals, such as \fBSIGINT\fR, which are sent to the target process. Such events are referred to as interrupts; signals generated by interrupts are said to be asynchronously generated. Asynchronously generated signals are not directed to a particular thread but are handled by an arbitrary thread that meets either of the following conditions: .RS +4 .TP .ie t \(bu .el o The thread is blocked in a call to \fBsigwait\fR(2) whose argument includes the type of signal generated. .RE .RS +4 .TP .ie t \(bu .el o The thread has a signal mask that does not include the type of signal generated. See \fBpthread_sigmask\fR(3C). Each process can specify a system action to be taken in response to each signal sent to it, called the signal's disposition. All threads in the process share the disposition. The set of system signal actions for a process is initialized from that of its parent. Once an action is installed for a specific signal, it usually remains installed until another disposition is explicitly requested by a call to either \fBsigaction()\fR, \fBsignal()\fR or \fBsigset()\fR, or until the process \fBexecs()\fR. See \fBsigaction\fR(2) and \fBsignal\fR(3C). When a process execs, all signals whose disposition has been set to catch the signal will be set to \fBSIG_DFL.\fR Alternatively, a process may request that the system automatically reset the disposition of a signal to \fBSIG_DFL\fR after it has been caught. See \fBsigaction\fR(2) and \fBsignal\fR(3C). .RE .SS "SIGNAL DELIVERY" .sp .LP A signal is said to be delivered to a process when a thread within the process takes the appropriate action for the disposition of the signal. Delivery of a signal can be blocked. There are two methods for handling delivery of a signal in a multithreaded application. The first method specifies a signal handler function to execute when the signal is received by the process. See \fBsigaction\fR(2). The second method uses \fBsigwait\fR(2) to create a thread to handle the receipt of the signal. The \fBsigaction()\fR function can be used for both synchronously and asynchronously generated signals. The \fBsigwait()\fR function will work only for asynchronously generated signals, as synchronously generated signals are sent to the thread that caused the event. The \fBsigwait()\fR function is the recommended for use with a multithreaded application. .SS "SIGNAL MASK" .sp .LP Each thread has a signal mask that defines the set of signals currently blocked from delivery to it. The signal mask of the main thread is inherited from the signal mask of the thread that created it in the parent process. The selection of the thread within the process that is to take the appropriate action for the signal is based on the method of signal generation and the signal masks of the threads in the receiving process. Signals that are generated by action of a particular thread such as hardware faults are delivered to the thread that caused the signal. See \fBpthread_sigmask\fR(3C) or \fBsigprocmask\fR(2). See \fBalarm\fR(2) for current semantics of delivery of \fBSIGALRM\fR. Signals that are directed to a particular thread are delivered to the targeted thread. See \fBpthread_kill\fR(3C). If the selected thread has blocked the signal, it remains pending on the thread until it is unblocked. For all other types of signal generation (for example, \fBkill\fR(2), \fBsigsend\fR(2), terminal activity, and other external events not ascribable to a particular thread) one of the threads that does not have the signal blocked is selected to process the signal. If all the threads within the process block the signal, it remains pending on the process until a thread in the process unblocks it. If the action associated with a signal is set to ignore the signal then both currently pending and subsequently generated signals of this type are discarded immediately for this process. .sp .LP The determination of which action is taken in response to a signal is made at the time the signal is delivered to a thread within the process, allowing for any changes since the time of generation. This determination is independent of the means by which the signal was originally generated. .sp .LP The signals currently defined by <\fBsignal.h\fR> are as follows: .sp .sp .TS c c c c l l l l . Name Value Default Event \fBSIGHUP\fR 1 Exit Hangup (see \fBtermio\fR(7I)) \fBSIGINT\fR 2 Exit Interrupt (see \fBtermio\fR(7I)) \fBSIGQUIT\fR 3 Core Quit (see \fBtermio\fR(7I)) \fBSIGILL\fR 4 Core Illegal Instruction \fBSIGTRAP\fR 5 Core Trace or Breakpoint Trap \fBSIGABRT\fR 6 Core Abort \fBSIGEMT\fR 7 Core Emulation Trap \fBSIGFPE\fR 8 Core Arithmetic Exception \fBSIGKILL\fR 9 Exit Killed \fBSIGBUS\fR 10 Core Bus Error \fBSIGSEGV\fR 11 Core Segmentation Fault \fBSIGSYS\fR 12 Core Bad System Call \fBSIGPIPE\fR 13 Exit Broken Pipe \fBSIGALRM\fR 14 Exit Alarm Clock \fBSIGTERM\fR 15 Exit Terminated \fBSIGUSR1\fR 16 Exit User Signal 1 \fBSIGUSR2\fR 17 Exit User Signal 2 \fBSIGCHLD\fR 18 Ignore Child Status Changed \fBSIGPWR\fR 19 Ignore Power Fail or Restart \fBSIGWINCH\fR 20 Ignore Window Size Change \fBSIGURG\fR 21 Ignore Urgent Socket Condition \fBSIGPOLL\fR 22 Exit Pollable Event (see \fBstreamio\fR(7I)) \fBSIGSTOP\fR 23 Stop Stopped (signal) \fBSIGTSTP\fR 24 Stop Stopped (user) (see \fBtermio\fR(7I)) \fBSIGCONT\fR 25 Ignore Continued \fBSIGTTIN\fR 26 Stop Stopped (tty input) (see \fBtermio\fR(7I)) \fBSIGTTOU\fR 27 Stop Stopped (tty output) (see \fBtermio\fR(7I)) \fBSIGVTALRM\fR 28 Exit Virtual Timer Expired \fBSIGPROF\fR 29 Exit Profiling Timer Expired \fBSIGXCPU\fR 30 Core T{ CPU time limit exceeded (see \fBgetrlimit\fR(2)) T} \fBSIGXFSZ\fR 31 Core T{ File size limit exceeded (see \fBgetrlimit\fR(2)) T} \fBSIGWAITING\fR 32 Ignore Reserved \fBSIGLWP\fR 33 Ignore Reserved \fBSIGFREEZE\fR 34 Ignore Check point Freeze \fBSIGTHAW\fR 35 Ignore Check point Thaw \fBSIGCANCEL\fR 36 Ignore Reserved for threading support \fBSIGLOST\fR 37 Exit T{ Resource lost (for example, record-lock lost) T} \fBSIGXRES\fR 38 Ignore T{ Resource control exceeded (see \fBsetrctl\fR(2)) T} \fBSIGJVM1\fR 39 Ignore Reserved for Java Virtual Machine 1 \fBSIGJVM2\fR 40 Ignore Reserved for Java Virtual Machine 2 \fBSIGRTMIN\fR \fB*\fR Exit First real time signal (\fBSIGRTMIN\fR+1) * Exit Second real time signal \fB\|.\|.\|.\fR (\fBSIGRTMAX\fR-1) * Exit Second-to-last real time signal \fBSIGRTMAX\fR \fB*\fR Exit Last real time signal .TE .sp .LP The symbols \fBSIGRTMIN\fR through \fBSIGRTMAX\fR are evaluated dynamically to permit future configurability. .sp .LP Applications should not use any of the signals marked "reserved" in the above table for any purpose, to avoid interfering with their use by the system. .SS "SIGNAL DISPOSITION" .sp .LP A process using a \fBsignal\fR(3C), \fBsigset\fR(3C) or \fBsigaction\fR(2) system call can specify one of three dispositions for a signal: take the default action for the signal, ignore the signal, or catch the signal. .SS "Default Action: SIG_DFL" .sp .LP A disposition of \fBSIG_DFL\fR specifies the default action. The default action for each signal is listed in the table above and is selected from the following: .sp .ne 2 .na \fBExit\fR .ad .RS 10n When it gets the signal, the receiving process is to be terminated with all the consequences outlined in \fBexit\fR(2). .RE .sp .ne 2 .na \fBCore\fR .ad .RS 10n When it gets the signal, the receiving process is to be terminated with all the consequences outlined in \fBexit\fR(2). In addition, a ``core image'' of the process is constructed in the current working directory. .RE .sp .ne 2 .na \fBStop\fR .ad .RS 10n When it gets the signal, the receiving process is to stop. When a process is stopped, all the threads within the process also stop executing. .RE .sp .ne 2 .na \fBIgnore\fR .ad .RS 10n When it gets the signal, the receiving process is to ignore it. This is identical to setting the disposition to \fBSIG_IGN\fR. .RE .SS "Ignore Signal: SIG_IGN" .sp .LP A disposition of \fBSIG_IGN\fR specifies that the signal is to be ignored. Setting a signal action to \fBSIG_IGN\fR for a signal that is pending causes the pending signal to be discarded, whether or not it is blocked. Any queued values pending are also discarded, and the resources used to queue them are released and made available to queue other signals. .SS "Catch Signal: function address" .sp .LP A disposition that is a function address specifies that, when it gets the signal, the thread within the process that is selected to process the signal will execute the signal handler at the specified address. Normally, the signal handler is passed the signal number as its only argument. If the disposition was set with the \fBsigaction\fR(2) function, however, additional arguments can be requested. When the signal handler returns, the receiving process resumes execution at the point it was interrupted, unless the signal handler makes other arrangements. If an invalid function address is specified, results are undefined. .sp .LP If the disposition has been set with the \fBsigset()\fR or \fBsigaction()\fR, the signal is automatically blocked in the thread while it is executing the signal catcher. If a \fBlongjmp()\fR is used to leave the signal catcher, then the signal must be explicitly unblocked by the user. See \fBsetjmp\fR(3C), \fBsignal\fR(3C) and \fBsigprocmask\fR(2). .sp .LP If execution of the signal handler interrupts a blocked function call, the handler is executed and the interrupted function call returns \fB\(mi1\fR to the calling process with \fBerrno\fR set to \fBEINTR\fR. If the \fBSA_RESTART\fR flag is set, however, certain function calls will be transparently restarted. .sp .LP Some signal-generating functions, such as high resolution timer expiration, asynchronous I/O completion, inter-process message arrival, and the \fBsigqueue\fR(3C) function, support the specification of an application defined value, either explicitly as a parameter to the function, or in a \fBsigevent\fR structure parameter. The \fBsigevent\fR structure is defined by \fB\fR and contains at least the following members: .sp .sp .TS c c c l l l . Type Name Description _ \fBint\fR \fBsigev_notify\fR Notification type \fBint\fR \fBsigev_signo\fR Signal number _ \fBunion sigval\fR \fBsigev_value\fR Signal value _ \fBvoid(*)(union sigval)\fR \fBsigev_notify_function\fR Notification function _ \fB(pthread_attr_t *)\fR \fBsigev_notify_attributes\fR Notification attributes .TE .sp .LP The \fBsigval\fR union is defined by \fB\fRand contains at least the following members: .sp .sp .TS c c c l l l . Type Name Description _ \fBint\fR \fBsival_int\fR Integer signal value \fBvoid *\fR \fBsival_ptr\fR Pointer signal value .TE .sp .LP The \fBsigev_notify\fR member specifies the notification mechanism to use when an asynchronous event occurs. The \fBsigev_notify\fR member may be defined with the following values: .sp .ne 2 .na \fB\fBSIGEV_NONE\fR\fR .ad .RS 16n No asynchronous notification is delivered when the event of interest occurs. .RE .sp .ne 2 .na \fB\fBSIGEV_SIGNAL\fR\fR .ad .RS 16n A queued signal, with its value equal to \fBsigev_signo\fR, is generated when the event of interest occurs. .RE .sp .ne 2 .na \fB\fBSIGEV_THREAD\fR\fR .ad .RS 16n The \fBsigev_notify_function\fR is called, with \fBsigev_value\fR as its argument, to perform notification when the asynchronous event occurs. The function is executed in an environment as if it were the start routine for a newly created thread with thread attributes \fBsigev_notify_attributes\fR. If \fBsigev_notify_attributes\fR is \fINULL\fR, the thread runs as a detached thread with default attributes. Otherwise, the thread runs with the specified attributes, but as a detached thread regardless. The thread runs with all blockable signals blocked. .RE .sp .ne 2 .na \fB\fBSIGEV_PORT\fR\fR .ad .RS 16n An asynchronous notification is delivered to an event port when the event of interest occurs. The \fBsigev_value.sival_ptr\fR member points to a \fBport_notify_t\fR structure defined in <\fBport.h\fR> (see \fBport_associate\fR(3C)). The event port identifier as well as an application-defined cookie are part of the \fBport_notify_t\fR structure. .RE .sp .LP The \fBsigev_signo\fR member contains the application-defined value to be passed to the signal-catching function (for notification type \fBSIGEV_SIGNAL\fR) at the time of the signal delivery as the \fBsi_value\fR member of the \fBsiginfo_t\fR structure, or as the argument to the notification function (for notification type \fBSIGEV_THREAD\fR) that is called when the asynchronous event occurs. For notification type \fBSIGEV_PORT\fR, \fBsigev_value.sival_ptr\fR points to a \fBport_notify_t\fR structure that specifies the port and an application-defined cookie. .sp .LP The \fBsigev_value\fR member references the application defined value to be passed to the signal-catching function at the time of the signal delivery as the \fBsi_value\fR member of the \fBsiginfo_t\fR structure. .sp .LP The \fBsival_int\fR member is used when the application defined value is of type \fBint\fR, and the \fBsival_ptr\fR member is used when the application defined value is a pointer. .sp .LP When a signal is generated by \fBsigqueue\fR(3C) or any signal\(migenerating function which supports the specification of an application defined value, the signal is marked pending and, if the \fBSA_SIGINFO\fR flag is set for that signal, the signal is queued to the process along with the application specified signal value. Multiple occurrences of signals so generated are queued in FIFO order. If the \fBSA_SIGINFO\fR flag is not set for that signal, later occurrences of that signal's generation, when a signal is already queued, are silently discarded. .SH ATTRIBUTES .sp .LP See \fBattributes\fR(5) for descriptions of the following attributes: .sp .sp .TS box; c | c l | l . ATTRIBUTE TYPE ATTRIBUTE VALUE _ Interface Stability Committed _ Standard See \fBstandards\fR(5). .TE .SH SEE ALSO .sp .LP \fBlockd\fR(1M), \fBIntro\fR(2), \fBalarm\fR(2), \fBexit\fR(2), \fBfcntl\fR(2), \fBgetrlimit\fR(2), \fBioctl\fR(2), \fBkill\fR(2), \fBpause\fR(2), \fBsetrctl\fR(2), \fBsigaction\fR(2), \fBsigaltstack\fR(2), \fBsigprocmask\fR(2), \fBsigsend\fR(2), \fBsigsuspend\fR(2), \fBsigwait\fR(2), \fBport_associate\fR(3C), \fBpthread_create\fR(3C), \fBpthread_kill\fR(3C), \fBpthread_sigmask\fR(3C), \fBsetjmp\fR(3C), \fBsiginfo.h\fR(3HEAD), \fBsignal\fR(3C), \fBsigqueue\fR(3C), \fBsigsetops\fR(3C), \fBucontext.h\fR(3HEAD), \fBwait\fR(3C), \fBattributes\fR(5), \fBstandards\fR(5) .SH NOTES .sp .LP The dispositions of the \fBSIGKILL\fR and \fBSIGSTOP\fR signals cannot be altered from their default values. The system generates an error if this is attempted. .sp .LP The \fBSIGKILL\fR, \fBSIGSTOP\fR, and \fBSIGCANCEL\fR signals cannot be blocked. The system silently enforces this restriction. .sp .LP The \fBSIGCANCEL\fR signal cannot be directed to an individual thread using \fBpthread_kill\fR(3C), but it can be sent to a process using \fBkill\fR(2), \fBsigsend\fR(2), or \fBsigqueue\fR(3C). .sp .LP Whenever a process receives a \fBSIGSTOP\fR, \fBSIGTSTP\fR, \fBSIGTTIN\fR, or \fBSIGTTOU\fR signal, regardless of its disposition, any pending \fBSIGCONT\fR signal are discarded. .sp .LP Whenever a process receives a \fBSIGCONT\fR signal, regardless of its disposition, any pending \fBSIGSTOP\fR, \fBSIGTSTP\fR, \fBSIGTTIN\fR, and \fBSIGTTOU\fR signals is discarded. In addition, if the process was stopped, it is continued. .sp .LP \fBSIGPOLL\fR is issued when a file descriptor corresponding to a STREAMS file has a "selectable" event pending. See \fBIntro\fR(2). A process must specifically request that this signal be sent using the \fBI_SETSIG\fR \fBioctl\fR call. Otherwise, the process will never receive \fBSIGPOLL\fR. .sp .LP If the disposition of the \fBSIGCHLD\fR signal has been set with \fBsignal()\fR or \fBsigset()\fR, or with \fBsigaction()\fR and the \fBSA_NOCLDSTOP\fR flag has been specified, it will only be sent to the calling process when its children exit; otherwise, it will also be sent when the calling process's children are stopped or continued due to job control. .sp .LP The name \fBSIGCLD\fR is also defined in this header and identifies the same signal as \fBSIGCHLD\fR. \fBSIGCLD\fR is provided for backward compatibility, new applications should use \fBSIGCHLD\fR. .sp .LP The disposition of signals that are inherited as \fBSIG_IGN\fR should not be changed. .sp .LP Signals which are generated synchronously should not be masked. If such a signal is blocked and delivered, the receiving process is killed.