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Tests whether a specified signal is a member of the signal set.
#include <signal.h>int sigismember (const sigset_t *set, int sig_number);
set
The signal set.sig_number
The individual signal.
The sigismember function tests whether sig_number is a member of the signal set pointed to by set.This function operates on data objects that you can address by the application, not on any set of signals known to the system. For example, this function does not operate on the set blocked from delivery to a process or the set pending for a process.
1 Indicates success. The specified signal is a member of the specified set. 0 Indicates an error. The specified signal is not a member of the specified set.
Nonlocal goto with signal handling.
#include <setjmp.h>void siglongjmp (sigjmp_buf env, int value);
env
An address for a sigjmp_buf structure.value
A nonzero value.
This function restores the environment saved by the most recent call to sigsetjmp in the same process with the corresponding sigjmp_buf argument.All accessible objects have values when siglongjmp is called, with one exception: values of objects of automatic storage duration that changed between the sigsetjmp call and siglongjmp call are indeterminate.
Because it bypasses the usual function call and return mechanisms, siglongjmp executes correctly during interrupts, signals, and any of their associated functions. However, if you invoke siglongjmp from a nested signal handler (for example, from a function invoked as a result of a signal raised during the handling of another signal), the behavior is undefined.
The siglongjmp function restores the saved signal mask only if you initialize the env argument by a call to sigsetjmp with a nonzero savemask argument.
After siglongjmp is completed, program execution continues as if the corresponding call of sigsetjmp just returned the value specified by value. The siglongjmp function cannot cause sigsetjmp to return 0 (zero); if value is 0, sigsetjmp returns 1
See also sigsetjmp in this section.
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.
This 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 a OpenVMS exception or a signal to generate a UNIX style signal, user 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 in this section 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.
This 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 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.
This 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.
Sets 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.
This 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' current signal mask as part of the calling environment.
See also siglongjmp in this section.
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 Compaq 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 in this section 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 standard header file <signal.h> as follows:
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 Compaq 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.
The sigstack structure is defined in the <signal.h> header file.
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.
This 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 in this section.
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 as follows:
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.
Returns the sine of its radian argument.
#include <math.h>double sin (double x);
x
A radian expressed as a real number.
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