SIGEVENT
Section: Linux Programmer's Manual (7)Updated: 2017-07-13
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NAME
sigevent - structure for notification from asynchronous routinesSYNOPSIS
#include <signal.h> union sigval { /* Data passed with notification */ int sival_int; /* Integer value */ void *sival_ptr; /* Pointer value */ }; struct sigevent { int sigev_notify; /* Notification method */ int sigev_signo; /* Notification signal */ union sigval sigev_value; /* Data passed with notification */ void (*sigev_notify_function) (union sigval); /* Function used for thread notification (SIGEV_THREAD) */ void *sigev_notify_attributes; /* Attributes for notification thread (SIGEV_THREAD) */ pid_t sigev_notify_thread_id; /* ID of thread to signal (SIGEV_THREAD_ID) */ };
DESCRIPTION
The sigevent structure is used by various APIs to describe the way a process is to be notified about an event (e.g., completion of an asynchronous request, expiration of a timer, or the arrival of a message).
The definition shown in the SYNOPSIS is approximate: some of the fields in the sigevent structure may be defined as part of a union. Programs should employ only those fields relevant to the value specified in sigev_notify.
The sigev_notify field specifies how notification is to be performed. This field can have one of the following values:
- SIGEV_NONE
- A "null" notification: don't do anything when the event occurs.
- SIGEV_SIGNAL
- Notify the process by sending the signal specified in sigev_signo.
-
If the signal is caught with a signal handler that was registered using the
sigaction(2)
SA_SIGINFO
flag, then the following fields are set in the
siginfo_t
structure that is passed as the second argument of the handler:
-
- si_code
- This field is set to a value that depends on the API delivering the notification.
- si_signo
- This field is set to the signal number (i.e., the same value as in sigev_signo).
- si_value
- This field is set to the value specified in sigev_value.
-
- Depending on the API, other fields may also be set in the siginfo_t structure.
- The same information is also available if the signal is accepted using sigwaitinfo(2).
- SIGEV_THREAD
- Notify the process by invoking sigev_notify_function "as if" it were the start function of a new thread. (Among the implementation possibilities here are that each timer notification could result in the creation of a new thread, or that a single thread is created to receive all notifications.) The function is invoked with sigev_value as its sole argument. If sigev_notify_attributes is not NULL, it should point to a pthread_attr_t structure that defines attributes for the new thread (see pthread_attr_init(3)).
- SIGEV_THREAD_ID (Linux-specific)
- Currently used only by POSIX timers; see timer_create(2).
SEE ALSO
timer_create(2), aio_fsync(3), aio_read(3), aio_write(3), getaddrinfo_a(3), lio_listio(3), mq_notify(3), aio(7), pthreads(7)COLOPHON
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Time: 04:45:57 GMT, September 16, 2022
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