Manual browser: event(3)
| event(3) | Library Functions Manual | event(3) |
NAME
event -Core functions for waiting for and receiving events, and using event bases.
SYNOPSIS
#include <event2/event.h>Data Structures
struct event
Macros
#define _EVENT_LOG_DEBUG EVENT_LOG_DEBUG
Log severities
#define EVENT_LOG_DEBUG 0
Loop flags
#define EVLOOP_ONCE 0x01
event flags
#define EV_TIMEOUT 0x01
evtimer_* macros
#define evtimer_assign(ev, b, cb, arg) event_assign((ev), (b), -1, 0, (cb), (arg))
evsignal_* macros
#define evsignal_add(ev, tv) event_add((ev), (tv))
Typedefs
typedef void(* event_callback_fn )(evutil_socket_t, short, void *)
Enumerations
enum event_base_config_flag { EVENT_BASE_FLAG_NOLOCK = 0x01, EVENT_BASE_FLAG_IGNORE_ENV = 0x02, EVENT_BASE_FLAG_STARTUP_IOCP = 0x04, EVENT_BASE_FLAG_NO_CACHE_TIME = 0x08, EVENT_BASE_FLAG_EPOLL_USE_CHANGELIST = 0x10 }
Functions
void event_active (struct event *ev, int res, short ncalls)
Detailed Description
Core functions for waiting for and receiving events, and using event bases.Macro Definition Documentation
#define EV_ET 0x20
Select edge-triggered behavior, if supported by the backend.#define EV_PERSIST 0x10
Persistent event: won't get removed automatically when activated. When a persistent event with a timeout becomes activated, its timeout is reset to 0.#define EV_TIMEOUT 0x01
Indicates that a timeout has occurred. It's not necessary to pass this flag to event_for new()/event_assign() to get a timeout.#define EVENT_MAX_PRIORITIES 256
Largest number of priorities that Libevent can support.#define EVLOOP_NONBLOCK 0x02
Do not block: see which events are ready now, run the callbacks of the highest-priority ones, then exit.#define EVLOOP_ONCE 0x01
Block until we have an active event, then exit once all active events have had their callbacks run.#define LIBEVENT_VERSION _EVENT_VERSION
As event_get_version, but gives the version of Libevent's headers.#define LIBEVENT_VERSION_NUMBER _EVENT_NUMERIC_VERSION
As event_get_version_number, but gives the version number of Libevent's headers.Typedef Documentation
typedef void(* event_callback_fn)(evutil_socket_t, short, void *)
A callback function for an event. It receives three arguments:Parameters:
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typedef void(* event_fatal_cb)(int err)
A function to be called if Libevent encounters a fatal internal error. See Also:
typedef void(* event_log_cb)(int severity, const char *msg)
A callback function used to intercept Libevent's log messages. See Also:
Enumeration Type Documentation
enum event_base_config_flag
A flag passed to event_config_set_flag(). These flags change the behavior of an allocated event_base.See Also:
Enumerator
- EVENT_BASE_FLAG_NOLOCK
- Do not allocate a lock for the event base, even if we have locking set up.
- EVENT_BASE_FLAG_IGNORE_ENV
- Do not check the EVENT_* environment variables when configuring an event_base.
- EVENT_BASE_FLAG_STARTUP_IOCP
- Windows only: enable the IOCP dispatcher at startup. If this flag is set then bufferevent_socket_new() and evconn_listener_new() will use IOCP-backed implementations instead of the usual select-based one on Windows.
- EVENT_BASE_FLAG_NO_CACHE_TIME
- Instead of checking the current time every time the event loop is ready to run timeout callbacks, check after each timeout callback.
- EVENT_BASE_FLAG_EPOLL_USE_CHANGELIST
- If we are using the epoll backend, this flag says that it is safe to use Libevent's internal change-list code to batch up adds and deletes in order to try to do as few syscalls as possible. Setting this flag can make your code run faster, but it may trigger a Linux bug: it is not safe to use this flag if you have any fds cloned by dup() or its variants. Doing so will produce strange and hard-to-diagnose bugs.
This flag can also be activated by settnig the EVENT_EPOLL_USE_CHANGELIST environment variable.
This flag has no effect if you wind up using a backend other than epoll.
enum event_method_feature
A flag used to describe which features an event_base (must) provide. Because of OS limitations, not every Libevent backend supports every possible feature. You can use this type with event_config_require_features() to tell Libevent to only proceed if your event_base implements a given feature, and you can receive this type from event_base_get_features() to see which features are available.
Enumerator
- EV_FEATURE_ET
- Require an event method that allows edge-triggered events with EV_ET.
- EV_FEATURE_O1
- Require an event method where having one event triggered among many is [approximately] an O(1) operation. This excludes (for example) select and poll, which are approximately O(N) for N equal to the total number of possible events.
- EV_FEATURE_FDS
- Require an event method that allows file descriptors as well as sockets.
Function Documentation
void event_active (struct event *ev, intres, shortncalls)
Make an event active. You can use this function on a pending or a non-pending event to make it active, so that its callback will be run by event_base_dispatch() or event_base_loop().One common use in multithreaded programs is to wake the thread running event_base_loop() from another thread.
Parameters:
int event_add (struct event *ev, const struct timeval *timeout)
Add an event to the set of pending events. The function event_add() schedules the execution of the ev event when the event specified in event_assign()/event_new() occurs, or when the time specified in timeout has elapesed. If atimeout is NULL, no timeout occurs and the function will only be called if a matching event occurs. The event in the ev argument must be already initialized by event_assign() or event_new() and may not be used in calls to event_assign() until it is no longer pending.If the event in the ev argument already has a scheduled timeout, calling event_add() replaces the old timeout with the new one, or clears the old timeout if the timeout argument is NULL.
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int event_assign (struct event *, struct event_base *, evutil_socket_t, short, event_callback_fn, void *)
Prepare a new, already-allocated event structure to be added. The function event_assign() prepares the event structure ev to be used in future calls to event_add() and event_del(). Unlike event_new(), it doesn't allocate memory itself: it requires that you have already allocated a struct event, probably on the heap. Doing this will typically make your code depend on the size of the event structure, and thereby create incompatibility with future versions of Libevent.The easiest way to avoid this problem is just to use event_new() and event_free() instead.
A slightly harder way to future-proof your code is to use event_get_struct_event_size() to determine the required size of an event at runtime.
Note that it is NOT safe to call this function on an event that is active or pending. Doing so WILL corrupt internal data structures in Libevent, and lead to strange, hard-to-diagnose bugs. You can use event_assign to change an existing event, but only if it is not active or pending!
The arguments for this function, and the behavior of the events that it makes, are as for event_new().
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int event_base_dispatch (struct event_base *)
Event dispatching loop. This loop will run the event base until either there are no more added events, or until something calls event_base_loopbreak() or event_base_loopexit().Parameters:
Returns:
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void event_base_free (struct event_base *)
Deallocate all memory associated with an event_base, and free the base. Note that this function will not close any fds or free any memory passed to event_new as the argument to callback.Parameters:
int event_base_get_features (const struct event_base *base)
Return a bitmask of the features implemented by an event base. This will be a bitwise OR of one or more of the values of event_method_featureSee Also:
const char* event_base_get_method (const struct event_base *)
Get the kernel event notification mechanism used by Libevent. Parameters:Returns:
int event_base_gettimeofday_cached (struct event_base *base, struct timeval *tv)
Sets 'tv' to the current time (as returned by gettimeofday()), looking at the cached value in 'base' if possible, and calling gettimeofday() or clock_gettime() as appropriate if there is no cached time. Generally, this value will only be cached while actually processing event callbacks, and may be very inaccuate if your callbacks take a long time to execute.Returns 0 on success, negative on failure.
int event_base_got_break (struct event_base *)
Checks if the event loop was told to abort immediately by event_loopbreak(). This function will return true for an event_base at every point after event_loopbreak() is called, until the event loop is next entered.Parameters:
Returns:
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event_base_got_exit()
int event_base_got_exit (struct event_base *)
Checks if the event loop was told to exit by event_loopexit(). This function will return true for an event_base at every point after event_loopexit() is called, until the event loop is next entered.Parameters:
Returns:
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event_base_got_break()
struct timeval* event_base_init_common_timeout (struct event_base *base, const struct timeval *duration) [read]
Prepare an event_base to use a large number of timeouts with the same duration. Libevent's default scheduling algorithm is optimized for having a large number of timeouts with their durations more or less randomly distributed. But if you have a large number of timeouts that all have the same duration (for example, if you have a large number of connections that all have a 10-second timeout), then you can improve Libevent's performance by telling Libevent about it.To do this, call this function with the common duration. It will return a pointer to a different, opaque timeout value. (Don't depend on its actual contents!) When you use this timeout value in event_add(), Libevent will schedule the event more efficiently.
(This optimization probably will not be worthwhile until you have thousands or tens of thousands of events with the same timeout.)
int event_base_loop (struct event_base *, int)
Wait for events to become active, and run their callbacks. This is a more flexible version of event_base_dispatch().By default, this loop will run the event base until either there are no more added events, or until something calls event_base_loopbreak() or evenet_base_loopexit(). You can override this behavior with the 'flags' argument.
Parameters:
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int event_base_loopbreak (struct event_base *)
Abort the active event_base_loop() immediately. event_base_loop() will abort the loop after the next event is completed; event_base_loopbreak() is typically invoked from this event's callback. This behavior is analogous to the 'break;' statement.Subsequent invocations of event_loop() will proceed normally.
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int event_base_loopexit (struct event_base *, const struct timeval *)
Exit the event loop after the specified time. The next event_base_loop() iteration after the given timer expires will complete normally (handling all queued events) then exit without blocking for events again.Subsequent invocations of event_base_loop() will proceed normally.
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struct event_base* event_base_new (void) [read]
Create and return a new event_base to use with the rest of Libevent. Returns:See Also:
struct event_base* event_base_new_with_config (const struct event_config *) [read]
Initialize the event API. Use event_base_new_with_config() to initialize a new event base, taking the specified configuration under consideration. The configuration object can currently be used to avoid certain event notification mechanisms.Parameters:
Returns:
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int event_base_once (struct event_base *, evutil_socket_t, short, event_callback_fn, void *, const struct timeval *)
Schedule a one-time event. The function event_base_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.Note that in Libevent 2.0 and earlier, if the event is never triggered, the internal memory used to hold it will never be freed. This may be fixed in a later version of Libevent.
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int event_base_priority_init (struct event_base *, int)
Set the number of different event priorities. By default Libevent schedules all active events with the same priority. However, some time 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_base_priority_init() function. This function should be called before the first call to event_base_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.
Note that urgent-priority events can starve less-urgent events: after running all urgent-priority callbacks, Libevent checks for more urgent events again, before running less-urgent events. Less-urgent events will not have their callbacks run until there are no events more urgent than them that want to be active.
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int event_base_set (struct event_base *, struct event *)
Associate a different event base with an event. The event to be associated must not be currently active or pending.Parameters:
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int event_config_avoid_method (struct event_config *cfg, const char *method)
Enters an event method that should be avoided into the configuration. This can be used to avoid event mechanisms that do not support certain file descriptor types, or for debugging to avoid certain event mechanisms. An application can make use of multiple event bases to accommodate incompatible file descriptor types.Parameters:
Returns:
void event_config_free (struct event_config *cfg)
Deallocates all memory associated with an event configuration object. Parameters:
struct event_config* event_config_new (void) [read]
Allocates a new event configuration object. The event configuration object can be used to change the behavior of an event base.Returns:
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int event_config_require_features (struct event_config *cfg, intfeature)
Enters a required event method feature that the application demands. Note that not every feature or combination of features is supported on every platform. Code that requests features should be prepared to handle the case where event_base_new_with_config() returns NULL, as in:
event_config_require_features(cfg, EV_FEATURE_ET);
base = event_base_new_with_config(cfg);
if (base == NULL) {
We can't get edge-triggered behavior here.
event_config_require_features(cfg, 0);
base = event_base_new_with_config(cfg);
}
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int event_config_set_flag (struct event_config *cfg, intflag)
Sets one or more flags to configure what parts of the eventual event_base will be initialized, and how they'll work. See Also:
int event_config_set_num_cpus_hint (struct event_config *cfg, intcpus)
Records a hint for the number of CPUs in the system. This is used for tuning thread pools, etc, for optimal performance. In Libevent 2.0, it is only on Windows, and only when IOCP is in use.Parameters:
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void event_debug_unassign (struct event *)
When debugging mode is enabled, informs Libevent that an event should no longer be considered as assigned. When debugging mode is not enabled, does nothing.This function must only be called on a non-added event.
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int event_del (struct event *)
Remove an event from the set of monitored events. 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.Parameters:
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void event_enable_debug_mode (void)
Enable some relatively expensive debugging checks in Libevent that would normally be turned off. Generally, these checks cause code that would otherwise crash mysteriously to fail earlier with an assertion failure. Note that this method MUST be called before any events or event_bases have been created.Debug mode can currently catch the following errors: An event is re-assigned while it is added Any function is called on a non-assigned event
Note that debugging mode uses memory to track every event that has been initialized (via event_assign, event_set, or event_new) but not yet released (via event_free or event_debug_unassign). If you want to use debug mode, and you find yourself running out of memory, you will need to use event_debug_unassign to explicitly stop tracking events that are no longer considered set-up.
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void event_free (struct event *)
Deallocate a struct event * returned by event_new(). If the event is pending or active, first make it non-pending and non-active.void event_get_assignment (const struct event *event, struct event_base **base_out, evutil_socket_t *fd_out, short *events_out, event_callback_fn *callback_out, void **arg_out)
Extract all of arguments given to construct a given event. The event_base is copied into *base_out, the fd is copied into *fd_out, and so on.If any of the '_out' arguments is NULL, it will be ignored.
size_t event_get_struct_event_size (void)
Return the size of struct event that the Libevent library was compiled with. This will be NO GREATER than sizeof(struct event) if you're running with the same version of Libevent that your application was built with, but otherwise might not.Note that it might be SMALLER than sizeof(struct event) if some future version of Libevent adds extra padding to the end of struct event. We might do this to help ensure ABI-compatibility between different versions of Libevent.
const char** event_get_supported_methods (void)
Gets all event notification mechanisms supported by Libevent. This functions returns the event mechanism in order preferred by Libevent. Note that this list will include all backends that Libevent has compiled-in support for, and will not necessarily check your OS to see whether it has the required resources.Returns:
const char* event_get_version (void)
Get the Libevent version. Note that this will give you the version of the library that you're currently linked against, not the version of the headers that you've compiled against.Returns:
ev_uint32_t event_get_version_number (void)
Return a numeric representation of Libevent's version. Note that this will give you the version of the library that you're currently linked against, not the version of the headers you've used to compile.The format uses one byte each for the major, minor, and patchlevel parts of the version number. The low-order byte is unused. For example, version 2.0.1-alpha has a numeric representation of 0x02000100
int event_initialized (const struct event *ev)
Test if an event structure might be initialized. The event_initialized() function can be used to check if an event has been initialized.Warning: This function is only useful for distinguishing a a zeroed-out piece of memory from an initialized event, it can easily be confused by uninitialized memory. Thus, it should ONLY be used to distinguish an initialized event from zero.
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struct event* event_new (struct event_base *, evutil_socket_t, short, event_callback_fn, void *) [read]
Allocate and asssign a new event structure, ready to be added. The function event_new() returns a new event that can be used in future calls to event_add() and event_del(). The fd and events arguments determine which conditions will trigger the event; the callback and callback_arg arguments tell Libevent what to do when the event becomes active.If events contains one of EV_READ, EV_WRITE, or EV_READ|EV_WRITE, then fd is a file descriptor or socket that should get monitored for readiness to read, readiness to write, or readiness for either operation (respectively). If events contains EV_SIGNAL, then fd is a signal number to wait for. If events contains none of those flags, then the event can be triggered only by a timeout or by manual activation with event_active(): In this case, fd must be -1.
The EV_PERSIST flag can also be passed in the events argument: it makes event_add() persistent until event_del() is called.
The EV_ET flag is compatible with EV_READ and EV_WRITE, and supported only by certain backends. It tells Libevent to use edge-triggered events.
The EV_TIMEOUT flag has no effect here.
It is okay to have multiple events all listening on the same fds; but they must either all be edge-triggered, or all not be edge triggerd.
When the event becomes active, the event loop will run the provided callbuck function, with three arguments. The first will be the provided fd value. The second will be a bitfield of the events that triggered: EV_READ, EV_WRITE, or EV_SIGNAL. Here the EV_TIMEOUT flag indicates that a timeout occurred, and EV_ET indicates that an edge-triggered event occurred. The third event will be the callback_arg pointer that you provide.
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int event_pending (const struct event *ev, shortevents, struct timeval *tv)
Checks if a specific event is pending or scheduled. Parameters:Returns:
int event_priority_set (struct event *, int)
Assign a priority to an event. Parameters:Returns:
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int event_reinit (struct event_base *base)
Reinitialize the event base after a fork. Some event mechanisms do not survive across fork. The event base needs to be reinitialized with the event_reinit() function.Parameters:
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void event_set_fatal_callback (event_fatal_cbcb)
Override Libevent's behavior in the event of a fatal internal error. By default, Libevent will call exit(1) if a programming error makes it impossible to continue correct operation. This function allows you to supply another callback instead. Note that if the function is ever invoked, something is wrong with your program, or with Libevent: any subsequent calls to Libevent may result in undefined behavior.Libevent will (almost) always log an _EVENT_LOG_ERR message before calling this function; look at the last log message to see why Libevent has died.
void event_set_log_callback (event_log_cbcb)
Redirect Libevent's log messages. Parameters:NOTE: The function you provide must not call any other libevent functionality. Doing so can produce undefined behavior.
void event_set_mem_functions (void *(*)(size_t sz)malloc_fn, void *(*)(void *ptr, size_t sz)realloc_fn, void(*)(void *ptr)free_fn)
Override the functions that Libevent uses for memory management. Usually, Libevent uses the standard libc functions malloc, realloc, and free to allocate memory. Passing replacements for those functions to event_set_mem_functions() overrides this behavior.Note that all memory returned from Libevent will be allocated by the replacement functions rather than by malloc() and realloc(). Thus, if you have replaced those functions, it will not be appropriate to free() memory that you get from Libevent. Instead, you must use the free_fn replacement that you provided.
Note also that if you are going to call this function, you should do so before any call to any Libevent function that does allocation. Otherwise, those funtions will allocate their memory using malloc(), but then later free it using your provided free_fn.
Parameters:
Author
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