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); Linux-specific */ };
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)