man event (Fonctions bibliothèques) - event_init ,

NAME

event_init ,event_dispatch ,event_loop ,event_loopexit ,event_base_loop ,event_base_loopexit ,event_set ,event_add ,event_del ,event_once ,event_pending ,event_initialized ,event_priority_init ,event_priority_set ,evtimer_set ,evtimer_add ,evtimer_delevtimer_pending ,evtimer_initialized ,signal_set ,signal_add ,signal_delsignal_pending ,signal_initialized ,bufferevent_new ,bufferevent_free ,bufferevent_write ,bufferevent_write_buffer ,bufferevent_read ,bufferevent_enable ,bufferevent_disable ,bufferevent_settimeout ,evbuffer_new ,evbuffer_free ,evbuffer_add ,evbuffer_add_buffer ,evbuffer_add_printf ,evbuffer_drain ,evbuffer_write ,evbuffer_read ,evbuffer_find ,evbuffer_readline - execute a function when a specific event occurs

SYNOPSIS

#include <sys/time.h>#include <event.h>event_initevent_dispatchevent_loop int flagsevent_loopexit struct timeval *tvevent_base_loop struct event_base * int flagsevent_base_loopexit struct event_base * struct timeval *tvevent_set struct event *ev int fd short event void (*fn)(int, short, void *) void *argevent_add struct event *ev struct timeval *tvevent_del struct event *evevent_once int fd short event void (*fn)(int, short, void *) void *arg struct timeval *tvevent_pending struct event *ev short event struct timeval *tvevent_initialized struct event *evevent_priority_init int nprioritiesevent_priority_set struct event *ev int priorityevtimer_set struct event *ev void (*fn)(int, short, void *) void *argevtimer_add struct event *ev struct timeval *evtimer_del struct event *evevtimer_pending struct event *ev struct timeval *tvevtimer_initialized struct event *evsignal_set struct event *ev int signal void (*fn)(int, short, void *) void *argsignal_add struct event *ev struct timeval *signal_del struct event *evsignal_pending struct event *ev struct timeval *tvsignal_initialized struct event *evbufferevent_new int fd evbuffercb readcb evbuffercb writecb everrorcb void *cbargbufferevent_free struct bufferevent *bufevbufferevent_write struct bufferevent *bufev void *data size_t sizebufferevent_write_buffer struct bufferevent *bufev struct evbuffer *bufbufferevent_read struct bufferevent *bufev void *data size_t sizebufferevent_enable struct bufferevent *bufev short eventbufferevent_disable struct bufferevent *bufev short eventbufferevent_settimeout struct bufferevent *bufev int timeout_read int timeout_writeevbuffer_new voidevbuffer_free struct evbuffer *bufevbuffer_add struct evbuffer *buf u_char *data size_t sizeevbuffer_add_buffer struct evbuffer *dst struct evbuffer *srcevbuffer_add_printf struct evbuffer *buf char *fmt ...evbuffer_drain struct evbuffer *buf size_t sizeevbuffer_write struct evbuffer *buf int fdevbuffer_read struct evbuffer *buf int fd int sizeevbuffer_find struct evbuffer *buf u_char *data size_t sizeevbuffer_readline struct evbuffer *buf(*event_sigcb)(void) ;event_gotsig ;

DESCRIPTION

The event API provides a mechanism to execute a function when a specific event on a file descriptor occurs or after a given time has passed.

The event API needs to be initialized with event_init before it can be used.

In order to process events, an application needs to call event_dispatch . This function only returns on error, and should replace the event core of the application program.

In order to avoid races in signal handlers, the event API provides two variables: event_sigcb and event_gotsig . A signal handler sets event_gotsig to indicate that a signal has been received. The application sets event_sigcb to a callback function. After the signal handler sets event_gotsig , event_dispatch will execute the callback function to process received signals. The callback returns 1 when no events are registered any more. It can return -1 to indicate an error to the event library, causing event_dispatch to terminate with errno set to EINTR.

The event_loop function provides an interface for single pass execution of pending events. The flags EVLOOP_ONCE and EVLOOP_NONBLOCK are recognized. The event_loopexit function allows the loop to be terminated after some amount of time has passed. The parameter indicates the time after which the loop should terminate.

It is the responsibility of the caller to provide these functions with pre-allocated event structures.

The function event_set prepares the event structure ev to be used in future calls to event_add and event_del . The event will be prepared to call the function specified by the fn argument with an int argument indicating the file descriptor, a short argument indicating the type of event, and a void * argument given in the arg argument. The fd indicates the file descriptor that should be monitored for events. The events can be either EV_READ , EV_WRITE , or both. Indicating that an application can read or write from the file descriptor respectively without blocking.

The function fn will be called with the file descriptor that triggered the event and the type of event which will be either EV_TIMEOUT , EV_SIGNAL , EV_READ , or EV_WRITE . The additional flag EV_PERSIST makes an event_add persistent until event_del has been called.

Once initialized, the ev structure can be used repeatedly with event_add and event_del and does not need to be reinitialized unless the function called and/or the argument to it are to be changed. However, when an ev structure has been added to libevent using event_add the structure must persist until the event occurs (assuming EV_PERSIST is not set) or is removed using event_del . You may not reuse the same ev structure for multiple monitored descriptors; each descriptor needs its own ev .

The function event_add schedules the execution of the ev event when the event specified in event_set occurs or in at least the time specified in the tv . If tv is NULL, no timeout occurs and the function will only be called if a matching event occurs on the file descriptor. The event in the ev argument must be already initialized by event_set and may not be used in calls to event_set until it has timed out or been removed with event_del . If the event in the ev argument already has a scheduled timeout, the old timeout will be replaced by the new one.

The function event_del will cancel the event in the argument ev . If the event has already executed or has never been added the call will have no effect.

The function event_once is similar to event_set . However, it schedules a callback to be called exactly once and does not require the caller to prepare an event structure. This function supports EV_TIMEOUT , EV_READ and EV_WRITE .

The event_pending function can be used to check if the event specified by event is pending to run. If EV_TIMEOUT was specified and tv is not NULL , the expiration time of the event will be returned in tv .

The event_initialized macro can be used to check if an event has been initialized.

The functions evtimer_set , evtimer_add , evtimer_del , evtimer_initialized , and evtimer_pending are abbreviations for common situations where only a timeout is required. The file descriptor passed will be -1, and the event type will be EV_TIMEOUT .

The functions signal_set , signal_add , signal_del , signal_initialized , and signal_pending are abbreviations. The event type will be a persistent EV_SIGNAL . That means signal_set adds EV_PERSIST .

It is possible to disable support for epoll , kqueue , devpoll, poll or select by setting the environment variable EVENT_NOEPOLL , EVENT_NOKQUEUE , EVENT_NODEVPOLL, EVENT_NOPOLL or EVENT_NOSELECT . By setting the environment variable EVENT_SHOW_METHOD , libevent displays the kernel notification method that it uses.

EVENT PRIORITIES

By default libevent schedules all active events with the same priority. However, sometime it is desirable to process some events with a higher priority than others. For that reason, libevent supports strict priority queues. Active events with a lower priority are always processed before events with a higher priority.

The number of different priorities can be set initially with the event_priority_init function. This function should be called before the first call to event_dispatch . The event_priority_set function can be used to assign a priority to an event. By default, libevent assigns the middle priority to all events unless their priority is explicitly set.

THREAD SAFE EVENTS

Libevent

has experimental support for thread-safe events. When initializing the library via event_init , an event base is returned. This event base can be used in conjunction with calls to event_base_set event_base_dispatch , event_base_loop , and event_base_loopexit . event_base_set should be called after preparing an event with event_set , as event_set assigns the provided event to the most recently created event base.

BUFFERED EVENTS

libevent

provides an abstraction on top of the regular event callbacks. This abstraction is called a buffered event . A buffered event provides input and output buffer that get filled and drained automatically. The user of a buffered event no longer deals directly with the IO, but instead is reading from input and writing to output buffers.

A new bufferevent is created by bufferevent_new . The parameter fd specifies the file descriptor from which data is read and written to. This file descriptor is not allowed to be a pipe(2) . The next three parameters are callbacks. The read and write callback have the following form (*cb) struct bufferevent *bufev void *arg The argument is specified by the fourth parameter cbarg .

By default the buffered event is read enabled and will try to read from the file descriptor. The write callback is executed whenever the output buffer is drained below the write low watermark which is 0 by default.

The bufferevent_write function can be used to write data to the file descriptor. The data is appended to the output buffer and written to the descriptor automatically as it becomes available for writing. The bufferevent_read function is used to read data from the input buffer. Both functions return the amount of data written or read.

RETURN VALUES

Upon successful completion event_add and event_del return 0. Otherwise, -1 is returned and the global variable errno is set to indicate the error.

SEE ALSO

timeout(9) ,select(2) ,kqueue()

HISTORY

The event API manpage is based on the timeout() manpage by Artur Grabowski. The port of libevent to Windows is due to Michael A. Davis. Support for real-time signals is due to Taral.

AUTHORS

The event library was written by Niels Provos.

BUGS

This documentation is neither complete nor authoritative. If you are in doubt about the usage of this API then check the source code to find out how it works, write up the missing piece of documentation and send it to me for inclusion in this man page.