event

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

In order to process events, an application needs to call 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 API provides two variables: and A signal handler sets to indicate that a signal has been received. The application sets to a callback function. After the signal handler sets 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 library, causing to terminate with set to

The function provides an interface for single pass execution of pending events. The flags and are recognized. The 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 prepares the event structure to be used in future calls to and The event will be prepared to call the function specified by the argument with an argument indicating the file descriptor, a argument indicating the type of event, and a argument given in the argument. The indicates the file descriptor that should be monitored for events. The events can be either or both, indicating that an application can read or write from the file descriptor respectively without blocking.

The function will be called with the file descriptor that triggered the event and the type of event which will be either or The additional flag makes an persistent until has been called.

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

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

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

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

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

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

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

The functions and are abbreviations. The event type will be a persistent That means adds

It is possible to disable support for or by setting the environment variable or respectively. By setting the environment variable displays the kernel notification method that it uses.

By default schedules all active events with the same priority. However, sometimes it is desirable to process some events with a higher priority than others. For that reason, 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 function. This function should be called before the first call to The function can be used to assign a priority to an event. By default, assigns the middle priority to all events unless their priority is explicitly set.

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

provides an abstraction on top of the regular event callbacks. This abstraction is called a A buffered event provides input and output buffers 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 The parameter 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: The error callback has the following form: The argument is specified by the fourth parameter A pointer is returned on success, NULL on error. Both the read and the write callback may be NULL. The error callback has to be always provided.

Once initialized, the bufferevent structure can be used repeatedly with bufferevent_enable() and bufferevent_disable(). The flags parameter can be a combination of and When read enabled the bufferevent will try to read from the file descriptor and call the read callback. The write callback is executed whenever the output buffer is drained below the write low watermark, which is by default.

The 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 function is used to read data from the input buffer. Both functions return the amount of data written or read.

If multiple bases are in use, bufferevent_base_set() must be called before enabling the bufferevent for the first time.

provides a very thin HTTP layer that can be used both to host an HTTP server and also to make HTTP requests. An HTTP server can be created by calling When the HTTP server is no longer used, it can be freed via

To be notified of HTTP requests, a user needs to register callbacks with the HTTP server. This can be done by calling The second argument is the URI for which a callback is being registered. The corresponding callback will receive an object that contains all information about the request.

This section does not document all the possible function calls, please check for the public interfaces.

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

kqueue(2) poll(2) select(2) timeout(9)

The API manpage is based on the timeout(9) manpage by Artur Grabowski. The port of to Windows is due to Michael A. Davis. Support for real-time signals is due to Taral.

The library was written by Niels Provos.

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.