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Constructs the mask for a given signal number.
#include <signal.h>int sigmask (signum);
signum
The signal number for which the mask is to be constructed.
The sigmask function is used to contruct the mask for a given signum. This mask can be used with the sigblock function.
x The mask constructed for signum
Allows you to specify the way in which the signal sig is to be handled: use the default handling for the signal, ignore the signal, or call the signal handler at the address specified.
#include <signal.h>void (*signal (int sig, void (*func) (int))) (int);
sig
The number or mnemonic associated with a signal. This argument is usually one of the mnemonics defined in the <signal.h> header file.func
Either the action to take when the signal is raised, or the address of a function needed to handle the signal.
If func is the constant SIG_DFL, the action for the given signal is reset to the default action, which is to terminate the receiving process. If the argument is SIG_IGN, the signal is ignored. Not all signals can be ignored.If func is neither SIG_DFL nor SIG_IGN, it specifies the address of a signal-handling function. When the signal is raised, the addressed function is called with sig as its argument. When the addressed function returns, the interrupted process continues at the point of interruption. (This is called catching a signal. Signals are reset to SIG_DFL after they are caught, except as shown in Chapter 4.)
You must call the signal function each time you want to catch a signal.
See Section 4.2 for more information on signal handling.
To cause an OpenVMS exception or a signal to generate a UNIX style signal, OpenVMS condition handlers must return SS$_RESIGNAL upon receiving any exception that they do not want to handle. Returning SS$_CONTINUE prevents the correct generation of a UNIX style signal. See Chapter 4 for a list of OpenVMS exceptions that correspond to UNIX signals.
x The address of the function previously established to handle the signal. SIG_ERR Indicates that the sig argument is out of range.
Assigns mask to the current set of masked signals and then waits for a signal.
#include <signal.h>int sigpause (int mask);
mask
The signals to be blocked.
See the sigblock function for information about the mask argument.When control returns to sigpause , the function restores the previous set of masked signals, sets errno to EINTR, and returns - 1 to indicate an interrupt. The value EINTR is defined in the <errno.h> header file.
- 1 Indicates an interrupt. errno is set to EINTR.
Examines pending signals.
#include <signal.h>int sigpending (sigset_t *set);
set
A pointer to a sigset_t structure.
The sigpending function stores the set of signals that are blocked from delivery and pending to the calling process in the location pointed to by the set argument.Call either the sigemptyset or the sigfillset function at least once for each object of type sigset_t prior to any other use of that object. If you do not initialize an object in this way and supply an argument to the sigpending function, the result is undefined.
See also sigemptyset and sigfillset in this section.
0 Indicates success. - 1 Indicates an error; errno is set to the following value:
- SIGSEGV -- Bad mask argument.
Sets the current signal mask.
#include <signal.h>int sigprocmask (int how, const sigset_t *set, sigset_t *o_set);
how
An integer value that indicates how to change the set of masked signals. Use one of the following values:
SIG_BLOCK The resulting set is the union of the current set and the signal set pointed to by the set argument. SIG_UNBLOCK The resulting set is the intersection of the current set and the complement of the signal set pointed to by the set argument. SIG_SETMASK The resulting set is the signal set pointed to by the set argument. set
The signal set. If the value of the set argument is:
- Not NULL -- It points to a set of signals used to change the currently blocked set.
- NULL -- The value of the how argument is not significant, and the process signal mask is unchanged, so you can use the call to inquire about currently blocked signals.
o_set
A non-NULL pointer to the location where the signal mask in effect at the time of the call is stored.
The sigprocmask function is used to examine or change the signal mask of the calling process.Typically, use the sigprocmask SIG_BLOCK value to block signals during a critical section of code, then use the sigprocmask SIG_SETMASK value to restore the mask to the previous value returned by the sigprocmask SIG_BLOCK value.
If there are any unblocked signals pending after the call to the sigprocmask function, at least one of those signals is delivered before the sigprocmask function returns.
You cannot block SIGKILL or SIGSTOP signals with the sigprocmask function. If a program attempts to block one of these signals, the sigprocmask function gives no indication of the error.
The following example shows how to set the signal mask to block only the SIGINT signal from delivery:
#include <signal.h> int return_value; sigset_t newset; . . . sigemptyset(&newset); sigaddset(&newset, SIGINT); return_value = sigprocmask (SIG_SETMASK, &newset, NULL);
0 Indicates success. - 1 Indicates an error. The signal mask of the process is unchanged. errno is set to one of the following values:
- EINVAL -- The value of the how argument is not equal to one of the defined values.
- EFAULT -- The set or o_set argument points to a location outside the allocated address space of the process.
Removes the specified signal from the calling process's signal mask.
#include <signal.h>int sigrelse (int signal);
signal
The specified signal. The signal argument can be assigned any of the signals defined in the <signal.h> header file, except SIGKILL and SIGSTOP.
The sighold , sigrelse , and sigignore functions provide simplified signal management:
- The sighold function adds signal to the calling process's signal mask.
- The sigrelse function removes signal from the calling process's signal mask.
- The sigignore function sets the disposition of signal to SIG_IGN.
The sighold function, in conjunction with sigrelse and sigpause , can be used to establish critical regions of code that require the delivery of a signal to be temporarily deferred.
Upon success, the sigrelse function returns a value of 0. Otherwise, a value of - 1 is returned, and errno is set to indicate the error.
Note
These interfaces are provided for compatibility only. New programs should use sigaction and sigprocmask to control the disposition of signals.
0 Indicates success. - 1 Indicates an error; errno is set to the following value:
- EINVAL -- The value of the signal argument is either an invalid signal number or SIGKILL.
Sets a jump point for a nonlocal goto.
#include <setjmp.h>init sigsetjmp (sigjmp_buf env, int savemask);
env
An address for a sigjmp_buf structure.savemask
An integer value that specifies whether you need to save the current signal mask.
The sigsetjmp function saves its calling environment in its env argument for later use by the siglongjmp function.If the value of savemask is not 0 (zero), sigsetjmp also saves the process's current signal mask as part of the calling environment.
See also siglongjmp .
You cannot invoke the longjmp function from an OpenVMS condition handler. However, you may invoke longjmp from a signal handler that has been established for any signal supported by the HP C RTL, subject to the following nesting restrictions:
- The longjmp function will not work if you invoke it from nested signal handlers. The result of the longjmp function, when invoked from a signal handler that has been entered as a result of an exception generated in another signal handler, is undefined.
- Do not invoke the sigsetjmp function from a signal handler unless the associated longjmp is to be issued before the handling of that signal is completed.
- Do not invoke the longjmp function from within an exit handler (established with atexit or SYS$DCLEXH). Exit handlers are invoked after image tear-down, so the destination address of the longjmp no longer exists.
- Invoking longjmp from within a signal handler to return to the main thread of execution might leave your program in an inconsistent state. Possible side effects include the inability to perform I/O or to receive any more UNIX signals. Use siglongjmp instead.
0 Indicates success. nonzero The return is a call to the siglongjmp function.
Establishes those signals that are blocked from delivery.
#include <signal.h>int sigsetmask (int mask);
mask
The signals to be blocked.
See the sigblock function for information about the mask argument.
x The previous set of masked signals.
Defines an alternate stack on which to process signals. This allows the processing of signals in a separate environment from that of the current process. This function is nonreentrant.
#include <signal.h>int sigstack (struct sigstack *ss, struct sigstack *oss);
ss
If ss is not NULL, it specifies the address of a structure that holds a pointer to a designated section of memory to be used as a signal stack on which to deliver signals.oss
If oss is not NULL, it specifies the address of a structure in which the old value of the stack address is returned.
The sigstack structure is defined in the <signal.h> standard header file:
struct sigstack { char *ss_sp; int ss_onstack; };If the sigvec function specifies that the signal handler is to execute on the signal stack, the system checks to see if the process is currently executing on that stack. If the process is not executing on the signal stack, the system arranges a switch to the signal stack for the duration of the signal handler's execution. If the oss argument is not NULL, the current state of the signal stack is returned.
Signal stacks must be allocated an adequate amount of storage; they do not expand like the run-time stack. For example, if your signal handler calls printf or any similarly complex HP C RTL routine, at least 12,000 bytes of storage should be allocated for the signal stack. If the stack overflows, an error occurs.
ss_sp must point to at least four bytes before the end of the allocated memory area (see the example). This is architecture-dependent and possibly not portable to other machine architectures or operating systems.
0 Indicates success. - 1 Indicates failure.
#define ss_size 15000 static char mystack[ss_size]; struct sigstack ss = {&mystack + sizeof(mystack) - sizeof(void *), 1};
Atomically changes the set of blocked signals and waits for a signal.
#include <signal.h>int sigsuspend (const sigset_t *signal_mask);
signal_mask
A pointer to a set of signals.
The sigsuspend function replaces the signal mask of the process with the set of signals pointed to by the signal_mask argument. Then it suspends execution of the process until delivery of a signal whose action is either to execute a signal catching function or to terminate the process. You cannot block the SIGKILL or SIGSTOP signals with the sigsuspend function. If a program attempts to block either of these signals, sigsuspend gives no indication of the error.If delivery of a signal causes the process to terminate, sigsuspend does not return. If delivery of a signal causes a signal catching function to execute, sigsuspend returns after the signal catching function returns, with the signal mask restored to the set that existed prior to the call to sigsuspend .
The sigsuspend function sets the signal mask and waits for an unblocked signal as one atomic operation. This means that signals cannot occur between the operations of setting the mask and waiting for a signal. If a program invokes sigprocmask SIG_SETMASK and sigsuspend separately, a signal that occurs between these functions is often not noticed by sigsuspend .
In normal usage, a signal is blocked by using the sigprocmask function at the beginning of a critical section. The process then determines whether there is work for it to do. If there is no work, the process waits for work by calling sigsuspend with the mask previously returned by sigprocmask .
If a signal is caught by the calling process and control is returned from the signal handler, the calling process resumes execution after sigsuspend , which always returns a value of - 1 and sets errno to EINTR.
See also sigpause and sigprocmask .
Suspends a calling thread and waits for queued signals to arrive.
#include <signal.h>int sigtimedwait (const sigset_t set, siginfo_t *info, const struct timespec *timeout);
set
The set of signals to wait for.info
Pointer to a siginfo structure that is receiving data describing the signal, including any application-defined data specified when the signal was posted.timeout
A timeout for the wait. If timeout is NULL, the argument is ignored.
The sigtimedwait function behaves the same as the sigwaitinfo function except that if none of the signals specified by set are pending, sigtimedwait waits for the time interval specified in the timespec structure referenced by timeout. If the timespec structure pointed to by timeout is zero-valued and if none of the signals specified by set are pending, then sigtimedwait returns immediately with an error.See also sigwait and sigwaitinfo .
See Section 4.2 for more information on signal handling.
x Upon successful completion, the signal number selected is returned. - 1 Indicates that an error occurred; errno is set to one of the following values:
- EINVAL -- The timeout argument specified a tv_nsec value less than 0 or greater than or equal to 1 billion.
- EINTR -- The wait was interrupted by an unblocked, caught signal.
- EAGAIN -- No signal specified by set was generated within the specified timeout period.
Permanently assigns a handler for a specific signal.
#include <signal.h>int sigvec (int sigint, struct sigvec *sv, struct sigvec *osv);
sigint
The signal identifier.sv
Pointer to a sigvec structure (see the Description section).osv
If osv is not NULL, the previous handling information for the signal is returned.
If sv is not NULL, it specifies the address of a structure containing a pointer to a handler routine and mask to be used when delivering the specified signal, and a flag indicating whether the signal is to be processed on an alternative stack. If sv-->onstack has a value of 1, the system delivers the signal to the process on a signal stack specified with sigstack .The sigvec function establishes a handler that remains established until explicitly removed or until the image terminates.
The sigvec structure is defined in the <signal.h> header file:
struct sigvec { int (*handler)(); int mask; int onstack; };See Section 4.2 for more information on signal handling.
0 Indicates that the call succeeded. - 1 Indicates that an error occurred.
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