libvirt/src/util/virevent.c
Dominik Perpeet 9bf1cef737 docs: event impl. registration before hypervisor connection
Event implementations need to be registered before a connection to the
Hypervisor is opened, otherwise event handling can be impaired (e.g.
delayed messages). This fact is referenced in an e-mail [1], but should
also be noted in the documentation of the registration functions.

[1] https://www.redhat.com/archives/libvirt-users/2014-April/msg00011.html
2015-10-15 19:50:58 -04:00

321 lines
9.6 KiB
C

/*
* virevent.c: event loop for monitoring file handles
*
* Copyright (C) 2007, 2011-2014 Red Hat, Inc.
* Copyright (C) 2007 Daniel P. Berrange
*
* 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/>.
*
* Author: Daniel P. Berrange <berrange@redhat.com>
*/
#include <config.h>
#include "virevent.h"
#include "vireventpoll.h"
#include "virlog.h"
#include "virerror.h"
#include <stdlib.h>
VIR_LOG_INIT("util.event");
static virEventAddHandleFunc addHandleImpl;
static virEventUpdateHandleFunc updateHandleImpl;
static virEventRemoveHandleFunc removeHandleImpl;
static virEventAddTimeoutFunc addTimeoutImpl;
static virEventUpdateTimeoutFunc updateTimeoutImpl;
static virEventRemoveTimeoutFunc removeTimeoutImpl;
/*****************************************************
*
* Below this point are *PUBLIC* APIs for event
* loop integration with applications using libvirt.
* These API contracts cannot be changed.
*
*****************************************************/
/**
* virEventAddHandle:
*
* @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
*
* Register a callback for monitoring file handle events. This function
* requires that an event loop has previously been registered with
* virEventRegisterImpl() or virEventRegisterDefaultImpl().
*
* Returns -1 if the file handle cannot be registered, otherwise a handle
* watch number to be used for updating and unregistering for events.
*/
int
virEventAddHandle(int fd,
int events,
virEventHandleCallback cb,
void *opaque,
virFreeCallback ff)
{
if (!addHandleImpl)
return -1;
return addHandleImpl(fd, events, cb, opaque, ff);
}
/**
* virEventUpdateHandle:
*
* @watch: watch whose file handle to update
* @events: bitset of events to watch from virEventHandleType constants
*
* 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.
*/
void
virEventUpdateHandle(int watch, int events)
{
if (updateHandleImpl)
updateHandleImpl(watch, events);
}
/**
* virEventRemoveHandle:
*
* @watch: watch whose file handle to remove
*
* Unregister a callback from a file handle. This function
* requires that an event loop has previously been registered with
* virEventRegisterImpl() or virEventRegisterDefaultImpl().
*
* Returns -1 if the file handle was not registered, 0 upon success.
*/
int
virEventRemoveHandle(int watch)
{
if (!removeHandleImpl)
return -1;
return removeHandleImpl(watch);
}
/**
* virEventAddTimeout:
*
* @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
*
* 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.
*
* Returns -1 if the timer cannot be registered, a positive
* integer timer id upon success.
*/
int
virEventAddTimeout(int timeout,
virEventTimeoutCallback cb,
void *opaque,
virFreeCallback ff)
{
if (!addTimeoutImpl)
return -1;
return addTimeoutImpl(timeout, cb, opaque, ff);
}
/**
* virEventUpdateTimeout:
*
* @timer: timer id to change
* @timeout: time between events in milliseconds
*
* 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.
*/
void
virEventUpdateTimeout(int timer, int timeout)
{
if (updateTimeoutImpl)
updateTimeoutImpl(timer, timeout);
}
/**
* virEventRemoveTimeout:
*
* @timer: the timer id to remove
*
* Unregister a callback for a timer. This function
* requires that an event loop has previously been registered with
* virEventRegisterImpl() or virEventRegisterDefaultImpl().
*
* Returns -1 if the timer was not registered, 0 upon success.
*/
int
virEventRemoveTimeout(int timer)
{
if (!removeTimeoutImpl)
return -1;
return removeTimeoutImpl(timer);
}
/**
* virEventRegisterImpl:
* @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
*
* 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.
*/
void virEventRegisterImpl(virEventAddHandleFunc addHandle,
virEventUpdateHandleFunc updateHandle,
virEventRemoveHandleFunc removeHandle,
virEventAddTimeoutFunc addTimeout,
virEventUpdateTimeoutFunc updateTimeout,
virEventRemoveTimeoutFunc removeTimeout)
{
VIR_DEBUG("addHandle=%p updateHandle=%p removeHandle=%p "
"addTimeout=%p updateTimeout=%p removeTimeout=%p",
addHandle, updateHandle, removeHandle,
addTimeout, updateTimeout, removeTimeout);
addHandleImpl = addHandle;
updateHandleImpl = updateHandle;
removeHandleImpl = removeHandle;
addTimeoutImpl = addTimeout;
updateTimeoutImpl = updateTimeout;
removeTimeoutImpl = removeTimeout;
}
/**
* virEventRegisterDefaultImpl:
*
* 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.
*/
int virEventRegisterDefaultImpl(void)
{
VIR_DEBUG("registering default event implementation");
virResetLastError();
if (virEventPollInit() < 0) {
virDispatchError(NULL);
return -1;
}
virEventRegisterImpl(
virEventPollAddHandle,
virEventPollUpdateHandle,
virEventPollRemoveHandle,
virEventPollAddTimeout,
virEventPollUpdateTimeout,
virEventPollRemoveTimeout
);
return 0;
}
/**
* virEventRunDefaultImpl:
*
* 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.
*/
int virEventRunDefaultImpl(void)
{
VIR_DEBUG("running default event implementation");
virResetLastError();
if (virEventPollRunOnce() < 0) {
virDispatchError(NULL);
return -1;
}
return 0;
}