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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>
       #include <event2/event-config.h>
       #include <stdio.h>
       #include <event2/util.h>


   Data Structures
           struct event
           Structure to represent a single event.  struct event_base
           Structure to hold information and state for a Libevent dispatch
           loop.  struct event_config
           Configuration for an event_base.

   Macros
           #define _EVENT_LOG_DEBUG   EVENT_LOG_DEBUG
           #define _EVENT_LOG_ERR   EVENT_LOG_ERR
           #define _EVENT_LOG_MSG   EVENT_LOG_MSG
           #define _EVENT_LOG_WARN   EVENT_LOG_WARN
           #define event_get_signal(ev)   ((int)event_get_fd(ev))
           Get the signal number assigned to a signal event.  #define
           EVENT_MAX_PRIORITIES   256
           Largest number of priorities that Libevent can support.  #define
           EVENT_SET_MEM_FUNCTIONS_IMPLEMENTED
           This definition is present if Libevent was built with support for
           event_set_mem_functions()  #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.

       Log severities

               #define EVENT_LOG_DEBUG   0
               #define EVENT_LOG_MSG   1
               #define EVENT_LOG_WARN   2
               #define EVENT_LOG_ERR   3

       Loop flags
       These flags control the behavior of event_base_loop().

               #define EVLOOP_ONCE   0x01
               Block until we have an active event, then exit once all active
               events have had their callbacks run.  #define EVLOOP_NONBLOCK
               0x02
               Do not block: see which events are ready now, run the callbacks
               of the highest-priority ones, then exit.

       event flags
       Flags to pass to event_new(), event_assign(), event_pending(), and
       anything else with an argument of the form 'short events'

               #define EV_TIMEOUT   0x01
               Indicates that a timeout has occurred.  #define EV_READ   0x02
               Wait for a socket or FD to become readable.  #define EV_WRITE
               0x04
               Wait for a socket or FD to become writeable.  #define EV_SIGNAL
               0x08
               Wait for a POSIX signal to be raised.  #define EV_PERSIST
               0x10
               Persistent event: won't get removed automatically when
               activated.  #define EV_ET   0x20
               Select edge-triggered behavior, if supported by the backend.

       evtimer_* macros
       Aliases for working with one-shot timer events

               #define evtimer_assign(ev, b, cb, arg)   event_assign((ev),
               (b), -1, 0, (cb), (arg))
               #define evtimer_new(b, cb, arg)   event_new((b), -1, 0, (cb),
               (arg))
               #define evtimer_add(ev, tv)   event_add((ev), (tv))
               #define evtimer_del(ev)   event_del(ev)
               #define evtimer_pending(ev, tv)   event_pending((ev),
               EV_TIMEOUT, (tv))
               #define evtimer_initialized(ev)   event_initialized(ev)

       evsignal_* macros
       Aliases for working with signal events

               #define evsignal_add(ev, tv)   event_add((ev), (tv))
               #define evsignal_assign(ev, b, x, cb, arg)   event_assign((ev),
               (b), (x), EV_SIGNAL|EV_PERSIST, cb, (arg))
               #define evsignal_new(b, x, cb, arg)   event_new((b), (x),
               EV_SIGNAL|EV_PERSIST, (cb), (arg))
               #define evsignal_del(ev)   event_del(ev)
               #define evsignal_pending(ev, tv)   event_pending((ev),
               EV_SIGNAL, (tv))
               #define evsignal_initialized(ev)   event_initialized(ev)

   Typedefs
           typedef void(* event_callback_fn )(evutil_socket_t, short, void *)
           A callback function for an event.  typedef void(* event_fatal_cb
           )(int err)
           A function to be called if Libevent encounters a fatal internal
           error.  typedef void(* event_log_cb )(int severity, const char
           *msg)
           A callback function used to intercept Libevent's log messages.

   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 }
           A flag passed to event_config_set_flag().  enum
           event_method_feature { EV_FEATURE_ET = 0x01, EV_FEATURE_O1 = 0x02,
           EV_FEATURE_FDS = 0x04 }
           A flag used to describe which features an event_base (must)
           provide.

   Functions
           void event_active (struct event *ev, int res, short ncalls)
           Make an event active.  int event_add (struct event *ev, const
           struct timeval *timeout)
           Add an event to the set of pending events.  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.  int
           event_base_dispatch (struct event_base *)
           Event dispatching loop.  void event_base_dump_events (struct
           event_base *, FILE *)
           void event_base_free (struct event_base *)
           Deallocate all memory associated with an event_base, and free the
           base.  int event_base_get_features (const struct event_base *base)
           Return a bitmask of the features implemented by an event base.
           const char * event_base_get_method (const struct event_base *)
           Get the kernel event notification mechanism used by Libevent.  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.  int event_base_got_break (struct event_base *)
           Checks if the event loop was told to abort immediately by
           event_loopbreak().  int event_base_got_exit (struct event_base *)
           Checks if the event loop was told to exit by event_loopexit().
           struct timeval * event_base_init_common_timeout (struct event_base
           *base, const struct timeval *duration)
           Prepare an event_base to use a large number of timeouts with the
           same duration.  int event_base_loop (struct event_base *, int)
           Wait for events to become active, and run their callbacks.  int
           event_base_loopbreak (struct event_base *)
           Abort the active event_base_loop() immediately.  int
           event_base_loopexit (struct event_base *, const struct timeval *)
           Exit the event loop after the specified time.  struct event_base *
           event_base_new (void)
           Create and return a new event_base to use with the rest of
           Libevent.  struct event_base * event_base_new_with_config (const
           struct event_config *)
           Initialize the event API.  int event_base_once (struct event_base
           *, evutil_socket_t, short, event_callback_fn, void *, const struct
           timeval *)
           Schedule a one-time event.  int event_base_priority_init (struct
           event_base *, int)
           Set the number of different event priorities.  int event_base_set
           (struct event_base *, struct event *)
           Associate a different event base with an event.  int
           event_config_avoid_method (struct event_config *cfg, const char
           *method)
           Enters an event method that should be avoided into the
           configuration.  void event_config_free (struct event_config *cfg)
           Deallocates all memory associated with an event configuration
           object.  struct event_config * event_config_new (void)
           Allocates a new event configuration object.  int
           event_config_require_features (struct event_config *cfg, int
           feature)
           Enters a required event method feature that the application
           demands.  int event_config_set_flag (struct event_config *cfg, int
           flag)
           Sets one or more flags to configure what parts of the eventual
           event_base will be initialized, and how they'll work.  int
           event_config_set_num_cpus_hint (struct event_config *cfg, int cpus)
           Records a hint for the number of CPUs in the system.  void
           event_debug_unassign (struct event *)
           When debugging mode is enabled, informs Libevent that an event
           should no longer be considered as assigned.  int event_del (struct
           event *)
           Remove an event from the set of monitored events.  void
           event_enable_debug_mode (void)
           Enable some relatively expensive debugging checks in Libevent that
           would normally be turned off.  void event_free (struct event *)
           Deallocate a struct event * returned by event_new().  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.  struct
           event_base * event_get_base (const struct event *ev)
           Get the event_base associated with an event.  event_callback_fn
           event_get_callback (const struct event *ev)
           Return the callback assigned to an event.  void *
           event_get_callback_arg (const struct event *ev)
           Return the callback argument assigned to an event.  short
           event_get_events (const struct event *ev)
           Return the events (EV_READ, EV_WRITE, etc) assigned to an event.
           evutil_socket_t event_get_fd (const struct event *ev)
           Get the socket or signal assigned to an event, or -1 if the event
           has no socket.  size_t event_get_struct_event_size (void)
           Return the size of struct event that the Libevent library was
           compiled with.  const char ** event_get_supported_methods (void)
           Gets all event notification mechanisms supported by Libevent.
           const char * event_get_version (void)
           Get the Libevent version.  ev_uint32_t event_get_version_number
           (void)
           Return a numeric representation of Libevent's version.  int
           event_initialized (const struct event *ev)
           Test if an event structure might be initialized.  struct event *
           event_new (struct event_base *, evutil_socket_t, short,
           event_callback_fn, void *)
           Allocate and asssign a new event structure, ready to be added.  int
           event_pending (const struct event *ev, short events, struct timeval
           *tv)
           Checks if a specific event is pending or scheduled.  int
           event_priority_set (struct event *, int)
           Assign a priority to an event.  int event_reinit (struct event_base
           *base)
           Reinitialize the event base after a fork.  void
           event_set_fatal_callback (event_fatal_cb cb)
           Override Libevent's behavior in the event of a fatal internal
           error.  void event_set_log_callback (event_log_cb cb)
           Redirect Libevent's log messages.  void event_set_mem_functions
           (void *(*malloc_fn)(size_t sz), void *(*realloc_fn)(void *ptr,
           size_t sz), void(*free_fn)(void *ptr))
           Override the functions that Libevent uses for memory management.

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:
           fd An fd or signal
           events One or more EV_* flags
           arg A user-supplied argument.

       See Also:
           event_new()


   typedef void(* event_fatal_cb)(int err)
       A function to be called if Libevent encounters a fatal internal error.
       See Also:
           event_set_fatal_callback


   typedef void(* event_log_cb)(int severity, const char *msg)
       A callback function used to intercept Libevent's log messages. See
       Also:
           event_set_log_callback


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:
           event_config_set_flag(), event_base_new_with_config(),
           event_method_feature


       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:
           ev an event to make active.
           res a set of flags to pass to the event's callback.
           ncalls an obsolete argument: this is ignored.


   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.

       Parameters:
           ev an event struct initialized via event_set()
           timeout the maximum amount of time to wait for the event, or NULL
           to wait forever

       Returns:
           0 if successful, or -1 if an error occurred

       See Also:
           event_del(), event_assign(), event_new()


   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().

       Parameters:
           ev an event struct to be modified
           base the event base to which ev should be attached.
           fd the file descriptor to be monitored
           events desired events to monitor; can be EV_READ and/or EV_WRITE
           callback callback function to be invoked when the event occurs
           callback_arg an argument to be passed to the callback function

       Returns:
           0 if success, or -1 on invalid arguments.

       See Also:
           event_new(), event_add(), event_del(), event_base_once(),
           event_get_struct_event_size()


   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:
           base the event_base structure returned by event_base_new() or
           event_base_new_with_config()

       Returns:
           0 if successful, -1 if an error occurred, or 1 if no events were
           registered.

       See Also:
           event_base_loop()


   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:
           eb an event_base to be freed


   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_feature

       See Also:
           event_method_feature


   const char* event_base_get_method (const struct event_base *)
       Get the kernel event notification mechanism used by Libevent.
       Parameters:
           eb the event_base structure returned by event_base_new()

       Returns:
           a string identifying the kernel event mechanism (kqueue, epoll,
           etc.)


   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:
           eb the event_base structure returned by event_init()

       Returns:
           true if event_base_loopbreak() was called on this event base, or 0
           otherwise

       See Also:
           event_base_loopbreak()

           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:
           eb the event_base structure returned by event_init()

       Returns:
           true if event_base_loopexit() was called on this event base, or 0
           otherwise

       See Also:
           event_base_loopexit()

           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:
           eb the event_base structure returned by event_base_new() or
           event_base_new_with_config()
           flags any combination of EVLOOP_ONCE | EVLOOP_NONBLOCK

       Returns:
           0 if successful, -1 if an error occurred, or 1 if no events were
           registered.

       See Also:
           event_base_loopexit(), event_base_dispatch(), EVLOOP_ONCE,
           EVLOOP_NONBLOCK


   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.

       Parameters:
           eb the event_base structure returned by event_init()

       Returns:
           0 if successful, or -1 if an error occurred

       See Also:
           event_base_loopexit()


   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.

       Parameters:
           eb the event_base structure returned by event_init()
           tv the amount of time after which the loop should terminate, or
           NULL to exit after running all currently active events.

       Returns:
           0 if successful, or -1 if an error occurred

       See Also:
           event_base_loopbreak()


   struct event_base* event_base_new (void) [read]
       Create and return a new event_base to use with the rest of Libevent.
       Returns:
           a new event_base on success, or NULL on failure.

       See Also:
           event_base_free(), event_base_new_with_config()


   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:
           cfg the event configuration object

       Returns:
           an initialized event_base that can be used to registering events,
           or NULL if no event base can be created with the requested
           event_config.

       See Also:
           event_base_new(), event_base_free(), event_init(), event_assign()


   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.

       Parameters:
           base an event_base
           fd a file descriptor to monitor, or -1 for no fd.
           events event(s) to monitor; can be any of EV_READ | EV_WRITE, or
           EV_TIMEOUT
           callback callback function to be invoked when the event occurs
           arg an argument to be passed to the callback function
           timeout the maximum amount of time to wait for the event. NULL
           makes an EV_READ/EV_WRITE event make forever; NULL makes an
           EV_TIMEOUT event succees immediately.

       Returns:
           0 if successful, or -1 if an error occurred


   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.

       Parameters:
           eb the event_base structure returned by event_base_new()
           npriorities the maximum number of priorities

       Returns:
           0 if successful, or -1 if an error occurred

       See Also:
           event_priority_set()


   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:
           eb the event base
           ev the event

       Returns:
           0 on success, -1 on failure.


   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:
           cfg the event configuration object
           method the name of the event method to avoid

       Returns:
           0 on success, -1 on failure.


   void event_config_free (struct event_config *cfg)
       Deallocates all memory associated with an event configuration object.
       Parameters:
           cfg the event configuration object to be freed.


   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:
           an event_config object that can be used to store configuration, or
           NULL if an error is encountered.

       See Also:
           event_base_new_with_config(), event_config_free(), event_config


   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);
            }


       Parameters:
           cfg the event configuration object
           feature a bitfield of one or more event_method_feature values.
           Replaces values from previous calls to this function.

       Returns:
           0 on success, -1 on failure.

       See Also:
           event_method_feature, event_base_new_with_config()


   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:
           event_base_config_flags, event_base_new_with_config()


   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:
           cfg the event configuration object
           cpus the number of cpus

       Returns:
           0 on success, -1 on failure.


   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.

       See Also:
           event_enable_debug_mode()


   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:
           ev an event struct to be removed from the working set

       Returns:
           0 if successful, or -1 if an error occurred

       See Also:
           event_add()


   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.

       See Also:
           event_debug_unassign()


   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:
           an array with pointers to the names of support methods. The end of
           the array is indicated by a NULL pointer. If an error is
           encountered NULL is returned.


   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:
           a string containing the version number of Libevent


   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.

       Parameters:
           ev an event structure to be tested

       Returns:
           1 if the structure might be initialized, or 0 if it has not been
           initialized


   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.

       Parameters:
           base the event base to which the event should be attached.
           fd the file descriptor or signal to be monitored, or -1.
           events desired events to monitor: bitfield of EV_READ, EV_WRITE,
           EV_SIGNAL, EV_PERSIST, EV_ET.
           callback callback function to be invoked when the event occurs
           callback_arg an argument to be passed to the callback function

       Returns:
           a newly allocated struct event that must later be freed with
           event_free().

       See Also:
           event_free(), event_add(), event_del(), event_assign()


   int event_pending (const struct event *ev, shortevents, struct timeval *tv)
       Checks if a specific event is pending or scheduled. Parameters:
           ev an event struct previously passed to event_add()
           events the requested event type; any of EV_TIMEOUT|EV_READ|
           EV_WRITE|EV_SIGNAL
           tv if this field is not NULL, and the event has a timeout, this
           field is set to hold the time at which the timeout will expire.

       Returns:
           true if the event is pending on any of the events in 'what', (that
           is to say, it has been added), or 0 if the event is not added.


   int event_priority_set (struct event *, int)
       Assign a priority to an event. Parameters:
           ev an event struct
           priority the new priority to be assigned

       Returns:
           0 if successful, or -1 if an error occurred

       See Also:
           event_priority_init()


   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:
           base the event base that needs to be re-initialized

       Returns:
           0 if successful, or -1 if some events could not be re-added.

       See Also:
           event_base_new()


   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:
           cb a function taking two arguments: an integer severity between
           _EVENT_LOG_DEBUG and _EVENT_LOG_ERR, and a string. If cb is NULL,
           then the default log is used.

       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:
           malloc_fn A replacement for malloc.
           realloc_fn A replacement for realloc
           free_fn A replacement for free.


Author
       Generated automatically by Doxygen for libevent from the source code.



libevent                        Wed Apr 10 2013                       event(3)