libvirt-event: APIs for management of events

## libvirt-event

libvirt-event - APIs for management of events

Provides APIs for the management of events Copyright (C) 2006-2014 Red Hat, Inc. This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this library. If not, see <http://www.gnu.org/licenses/>.

## Synopsis

    typedef enum virEventHandleType;
    int	virEventAddHandle		(int fd,
    					 int events,
    					 virEventHandleCallback cb,
    					 void * opaque,
    					 virFreeCallback ff);
    typedef int virEventAddHandleFunc		(int fd,
    					 int event,
    					 virEventHandleCallback cb,
    					 void * opaque,
    					 virFreeCallback ff);
    int	virEventAddTimeout		(int timeout,
    					 virEventTimeoutCallback cb,
    					 void * opaque,
    					 virFreeCallback ff);
    typedef int virEventAddTimeoutFunc		(int timeout,
    					 virEventTimeoutCallback cb,
    					 void * opaque,
    					 virFreeCallback ff);
    typedef void virEventHandleCallback		(int watch,
    					 int fd,
    					 int events,
    					 void * opaque);
    int	virEventRegisterDefaultImpl	(void);
    void	virEventRegisterImpl		(virEventAddHandleFunc addHandle,
    					 virEventUpdateHandleFunc updateHandle,
    					 virEventRemoveHandleFunc removeHandle,
    					 virEventAddTimeoutFunc addTimeout,
    					 virEventUpdateTimeoutFunc updateTimeout,
    					 virEventRemoveTimeoutFunc removeTimeout);
    int	virEventRemoveHandle		(int watch);
    typedef int virEventRemoveHandleFunc	(int watch);
    int	virEventRemoveTimeout		(int timer);
    typedef int virEventRemoveTimeoutFunc	(int timer);
    int	virEventRunDefaultImpl		(void);
    typedef void virEventTimeoutCallback		(int timer,
    					 void * opaque);
    void	virEventUpdateHandle		(int watch,
    					 int events);
    typedef void virEventUpdateHandleFunc	(int watch,
    					 int event);
    void	virEventUpdateTimeout		(int timer,
    					 int timeout);
    typedef void virEventUpdateTimeoutFunc	(int timer,
    					 int timeout);

## Description

## Details

### Enum virEventHandleType

    enum virEventHandleType {
        VIR_EVENT_HANDLE_READABLE = 1
        VIR_EVENT_HANDLE_WRITABLE = 2
        VIR_EVENT_HANDLE_ERROR = 4
        VIR_EVENT_HANDLE_HANGUP = 8
    };

### Function type virEventAddHandleFunc

    int	virEventAddHandleFunc		(int fd,
    					 int event,
    					 virEventHandleCallback cb,
    					 void * opaque,
    					 virFreeCallback ff)

Part of the EventImpl, this callback adds a file handle callback to listen for specific events. The same file handle can be registered multiple times provided the requested event sets are non-overlapping If the opaque user data requires free'ing when the handle is unregistered, then a 2nd callback can be supplied for this purpose. This callback needs to be invoked from a clean stack. If 'ff' callbacks are invoked directly from the virEventRemoveHandleFunc they will likely deadlock in libvirt.

`fd`: | file descriptor to listen on
`event`: | bitset of events on which to fire the callback
`cb`: | the callback to be called when an event occurs
`opaque`: | user data to pass to the callback
`ff`: | the callback invoked to free opaque data blob
`Returns`: | -1 if the file handle cannot be registered, otherwise a handle watch number to be used for updating and unregistering for events

### Function type virEventAddTimeoutFunc

    int	virEventAddTimeoutFunc		(int timeout,
    					 virEventTimeoutCallback cb,
    					 void * opaque,
    					 virFreeCallback ff)

Part of the EventImpl, this user-defined callback handles adding an event timeout. If the opaque user data requires free'ing when the handle is unregistered, then a 2nd callback can be supplied for this purpose.

`timeout`: | The timeout to monitor
`cb`: | the callback to call when timeout has expired
`opaque`: | user data to pass to the callback
`ff`: | the callback invoked to free opaque data blob
`Returns`: | a timer value

### Function type virEventHandleCallback

    void	virEventHandleCallback		(int watch,
    					 int fd,
    					 int events,
    					 void * opaque)

Callback for receiving file handle events. The callback will be invoked once for each event which is pending.

`watch`: | watch on which the event occurred
`fd`: | file handle on which the event occurred
`events`: | bitset of events from virEventHandleType constants
`opaque`: | user data registered with handle

### Function type virEventRemoveHandleFunc

    int	virEventRemoveHandleFunc	(int watch)

Part of the EventImpl, this user-provided callback is notified when an fd is no longer being listened on. If a virEventHandleFreeFunc was supplied when the handle was registered, it will be invoked some time during, or after this function call, when it is safe to release the user data.

`watch`: | file descriptor watch to stop listening on
`Returns`: | -1 if the file handle was not registered, 0 upon success

### Function type virEventRemoveTimeoutFunc

    int	virEventRemoveTimeoutFunc	(int timer)

Part of the EventImpl, this user-defined callback removes a timer If a virEventTimeoutFreeFunc was supplied when the handle was registered, it will be invoked some time during, or after this function call, when it is safe to release the user data.

`timer`: | the timer to remove
`Returns`: | 0 on success, -1 on failure

### Function type virEventTimeoutCallback

    void	virEventTimeoutCallback		(int timer,
    					 void * opaque)

callback for receiving timer events

`timer`: | timer id emitting the event
`opaque`: | user data registered with handle

### Function type virEventUpdateHandleFunc

    void	virEventUpdateHandleFunc	(int watch,
    					 int event)

Part of the EventImpl, this user-provided callback is notified when events to listen on change

`watch`: | file descriptor watch to modify
`event`: | new events to listen on

### Function type virEventUpdateTimeoutFunc

    void	virEventUpdateTimeoutFunc	(int timer,
    					 int timeout)

Part of the EventImpl, this user-defined callback updates an event timeout.

`timer`: | the timer to modify
`timeout`: | the new timeout value

### virEventAddHandle ()

    int	virEventAddHandle		(int fd,
    					 int events,
    					 virEventHandleCallback cb,
    					 void * opaque,
    					 virFreeCallback ff)

Register a callback for monitoring file handle events. This function requires that an event loop has previously been registered with virEventRegisterImpl() or virEventRegisterDefaultImpl().

`fd`: | file handle to monitor for events
`events`: | bitset of events to watch from virEventHandleType constants
`cb`: | callback to invoke when an event occurs
`opaque`: | user data to pass to callback
`ff`: | callback to free opaque when handle is removed
`Returns`: | -1 if the file handle cannot be registered, otherwise a handle watch number to be used for updating and unregistering for events.

### virEventAddTimeout ()

    int	virEventAddTimeout		(int timeout,
    					 virEventTimeoutCallback cb,
    					 void * opaque,
    					 virFreeCallback ff)

Register a callback for a timer event. This function requires that an event loop has previously been registered with virEventRegisterImpl() or virEventRegisterDefaultImpl(). Setting @timeout to -1 will disable the timer. Setting @timeout to zero will cause it to fire on every event loop iteration.

`timeout`: | time between events in milliseconds
`cb`: | callback to invoke when an event occurs
`opaque`: | user data to pass to callback
`ff`: | callback to free opaque when timeout is removed
`Returns`: | -1 if the timer cannot be registered, a positive integer timer id upon success.

### virEventRegisterDefaultImpl ()

    int	virEventRegisterDefaultImpl	(void)

Registers a default event implementation based on the poll() system call. This is a generic implementation that can be used by any client application which does not have a need to integrate with an external event loop impl. For proper event handling, it is important that the event implementation is registered before a connection to the Hypervisor is opened. Once registered, the application has to invoke virEventRunDefaultImpl() in a loop to process events. Failure to do so may result in connections being closed unexpectedly as a result of keepalive timeout. The default event loop fully supports handle and timeout events, but only wakes up on events registered by libvirt API calls such as virEventAddHandle() or virConnectDomainEventRegisterAny().

`Returns`: | 0 on success, -1 on failure.

### virEventRegisterImpl ()

    void	virEventRegisterImpl		(virEventAddHandleFunc addHandle,
    					 virEventUpdateHandleFunc updateHandle,
    					 virEventRemoveHandleFunc removeHandle,
    					 virEventAddTimeoutFunc addTimeout,
    					 virEventUpdateTimeoutFunc updateTimeout,
    					 virEventRemoveTimeoutFunc removeTimeout)

Registers an event implementation, to allow integration with an external event loop. Applications would use this to integrate with the libglib2 event loop, or libevent or the QT event loop. For proper event handling, it is important that the event implementation is registered before a connection to the Hypervisor is opened. Use of the virEventAddHandle() and similar APIs require that the corresponding handler is registered. Use of the virConnectDomainEventRegisterAny() and similar APIs requires that the three timeout handlers are registered. Likewise, the three timeout handlers must be registered if the remote server has been configured to send keepalive messages, or if the client intends to call virConnectSetKeepAlive(), to avoid either side from unexpectedly closing the connection due to inactivity. If an application does not need to integrate with an existing event loop implementation, then the virEventRegisterDefaultImpl() method can be used to setup the generic libvirt implementation. Once registered, the event loop implementation cannot be changed, and must be run continuously. Note that callbacks may remain registered for a short time even after calling virConnectClose on all open connections, so it is not safe to stop running the event loop immediately after closing the connection.

`addHandle`: | the callback to add fd handles
`updateHandle`: | the callback to update fd handles
`removeHandle`: | the callback to remove fd handles
`addTimeout`: | the callback to add a timeout
`updateTimeout`: | the callback to update a timeout
`removeTimeout`: | the callback to remove a timeout

### virEventRemoveHandle ()

    int	virEventRemoveHandle		(int watch)

Unregister a callback from a file handle. This function requires that an event loop has previously been registered with virEventRegisterImpl() or virEventRegisterDefaultImpl().

`watch`: | watch whose file handle to remove
`Returns`: | -1 if the file handle was not registered, 0 upon success.

### virEventRemoveTimeout ()

    int	virEventRemoveTimeout		(int timer)

Unregister a callback for a timer. This function requires that an event loop has previously been registered with virEventRegisterImpl() or virEventRegisterDefaultImpl().

`timer`: | the timer id to remove
`Returns`: | -1 if the timer was not registered, 0 upon success.

### virEventRunDefaultImpl ()

    int	virEventRunDefaultImpl		(void)

Run one iteration of the event loop. Applications will generally want to have a thread which invokes this method in an infinite loop. Furthermore, it is wise to set up a pipe-to-self handler (via virEventAddHandle()) or a timeout (via virEventAddTimeout()) before calling this function, as it will block forever if there are no registered events. static bool quit; while (!quit) { if (virEventRunDefaultImpl() < 0) ...print error... }

`Returns`: | 0 on success, -1 on failure.

### virEventUpdateHandle ()

    void	virEventUpdateHandle		(int watch,
    					 int events)

Change event set for a monitored file handle. This function requires that an event loop has previously been registered with virEventRegisterImpl() or virEventRegisterDefaultImpl(). Will not fail if fd exists.

`watch`: | watch whose file handle to update
`events`: | bitset of events to watch from virEventHandleType constants

### virEventUpdateTimeout ()

    void	virEventUpdateTimeout		(int timer,
    					 int timeout)

Change frequency for a timer. This function requires that an event loop has previously been registered with virEventRegisterImpl() or virEventRegisterDefaultImpl(). Setting frequency to -1 will disable the timer. Setting the frequency to zero will cause it to fire on every event loop iteration. Will not fail if timer exists.

`timer`: | timer id to change
`timeout`: | time between events in milliseconds