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[Libvir] PATCH: Allow updating of timer & file handle event watches



The forthcoming patch to add Avahi support requires a couple of enhancements
to our event loop to support integration with Avahi's event callback needs

 - Ability to update the event mask for a pre-existing file handle watch
 - Ability to change the frequency of a timer watch
 - Ability to have a timer which fires immediately
 - Ability to disable events on a timer watch

The first point was trivial - just change the 'events' flag we have recorded
in the virEventHandle struct.

The second point was also trivial - just change the period of the timer as
recorded in virEventTimer struct.

The last two points were more tricky, but doable. To fire a timer immediately
I tweaked the logic so that it allows a frequency of '0'. Obviously to avoid
spinning 100%, the app should unregister the timer once it has fired the
desired number of times (usually 1). To disable a timer temporarily I allow
the use of '-1' in the frequency.

THe code had a bad mix of terminology using a 'timer' and 'timeout' field
in the virEventTimer struct which confused me no end. So I renamed the
'timeout' field to 'frequency' which reflects its actual purpose.

Finally, when building with debugging, the event loop can generate alot of
data, so I added a EVENT_DEBUG macro to the file which prefixes EVENT: on
all debug output so allow easy filtering.

Dan.
-- 
|=- Red Hat, Engineering, Emerging Technologies, Boston.  +1 978 392 2496 -=|
|=-           Perl modules: http://search.cpan.org/~danberr/              -=|
|=-               Projects: http://freshmeat.net/~danielpb/               -=|
|=-  GnuPG: 7D3B9505   F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505  -=| 
diff -r 0f29c3c9425f qemud/event.c
--- a/qemud/event.c	Mon Sep 17 05:23:04 2007 -0400
+++ b/qemud/event.c	Mon Sep 17 13:29:46 2007 -0400
@@ -30,6 +30,8 @@
 
 #include "internal.h"
 #include "event.h"
+
+#define EVENT_DEBUG(fmt, ...) qemudDebug("EVENT: " fmt, __VA_ARGS__)
 
 /* State for a single file handle being monitored */
 struct virEventHandle {
@@ -43,7 +45,7 @@ struct virEventHandle {
 /* State for a single timer being generated */
 struct virEventTimeout {
     int timer;
-    int timeout;
+    int frequency;
     unsigned long long expiresAt;
     virEventTimeoutCallback cb;
     void *opaque;
@@ -77,11 +79,11 @@ static int nextTimer = 0;
  * For this reason we only ever append to existing list.
  */
 int virEventAddHandleImpl(int fd, int events, virEventHandleCallback cb, void *opaque) {
-    qemudDebug("Add handle %d %d %p %p\n", fd, events, cb, opaque);
+    EVENT_DEBUG("Add handle %d %d %p %p", fd, events, cb, opaque);
     if (eventLoop.handlesCount == eventLoop.handlesAlloc) {
         struct virEventHandle *tmp;
-        qemudDebug("Used %d handle slots, adding %d more\n",
-                   eventLoop.handlesAlloc, EVENT_ALLOC_EXTENT);
+        EVENT_DEBUG("Used %d handle slots, adding %d more",
+                    eventLoop.handlesAlloc, EVENT_ALLOC_EXTENT);
         tmp = realloc(eventLoop.handles,
                       sizeof(struct virEventHandle) *
                       (eventLoop.handlesAlloc + EVENT_ALLOC_EXTENT));
@@ -103,6 +105,15 @@ int virEventAddHandleImpl(int fd, int ev
     return 0;
 }
 
+void virEventUpdateHandleImpl(int fd, int events) {
+    int i;
+    for (i = 0 ; i < eventLoop.handlesCount ; i++) {
+        if (eventLoop.handles[i].fd == fd) {
+            eventLoop.handles[i].events = events;
+        }
+    }
+}
+
 /*
  * Unregister a callback from a file handle
  * NB, it *must* be safe to call this from within a callback
@@ -111,13 +122,13 @@ int virEventAddHandleImpl(int fd, int ev
  */
 int virEventRemoveHandleImpl(int fd) {
     int i;
-    qemudDebug("Remove handle %d\n", fd);
+    EVENT_DEBUG("Remove handle %d", fd);
     for (i = 0 ; i < eventLoop.handlesCount ; i++) {
         if (eventLoop.handles[i].deleted)
             continue;
 
         if (eventLoop.handles[i].fd == fd) {
-            qemudDebug("mark delete %d\n", i);
+            EVENT_DEBUG("mark delete %d", i);
             eventLoop.handles[i].deleted = 1;
             return 0;
         }
@@ -131,17 +142,17 @@ int virEventRemoveHandleImpl(int fd) {
  * NB, it *must* be safe to call this from within a callback
  * For this reason we only ever append to existing list.
  */
-int virEventAddTimeoutImpl(int timeout, virEventTimeoutCallback cb, void *opaque) {
-    struct timeval tv;
-    qemudDebug("Adding timeout with %d ms period", timeout);
-    if (gettimeofday(&tv, NULL) < 0) {
+int virEventAddTimeoutImpl(int frequency, virEventTimeoutCallback cb, void *opaque) {
+    struct timeval now;
+    EVENT_DEBUG("Adding timer %d with %d ms freq", nextTimer, frequency);
+    if (gettimeofday(&now, NULL) < 0) {
         return -1;
     }
 
     if (eventLoop.timeoutsCount == eventLoop.timeoutsAlloc) {
         struct virEventTimeout *tmp;
-        qemudDebug("Used %d timeout slots, adding %d more\n",
-                   eventLoop.timeoutsAlloc, EVENT_ALLOC_EXTENT);
+        EVENT_DEBUG("Used %d timeout slots, adding %d more",
+                    eventLoop.timeoutsAlloc, EVENT_ALLOC_EXTENT);
         tmp = realloc(eventLoop.timeouts,
                       sizeof(struct virEventTimeout) *
                       (eventLoop.timeoutsAlloc + EVENT_ALLOC_EXTENT));
@@ -153,18 +164,37 @@ int virEventAddTimeoutImpl(int timeout, 
     }
 
     eventLoop.timeouts[eventLoop.timeoutsCount].timer = nextTimer++;
-    eventLoop.timeouts[eventLoop.timeoutsCount].timeout = timeout;
+    eventLoop.timeouts[eventLoop.timeoutsCount].frequency = frequency;
     eventLoop.timeouts[eventLoop.timeoutsCount].cb = cb;
     eventLoop.timeouts[eventLoop.timeoutsCount].opaque = opaque;
     eventLoop.timeouts[eventLoop.timeoutsCount].deleted = 0;
     eventLoop.timeouts[eventLoop.timeoutsCount].expiresAt =
-        timeout +
-        (((unsigned long long)tv.tv_sec)*1000) +
-        (((unsigned long long)tv.tv_usec)/1000);
+        frequency >= 0 ? frequency +
+        (((unsigned long long)now.tv_sec)*1000) +
+        (((unsigned long long)now.tv_usec)/1000) : 0;
 
     eventLoop.timeoutsCount++;
 
     return nextTimer-1;
+}
+
+void virEventUpdateTimeoutImpl(int timer, int frequency) {
+    struct timeval tv;
+    int i;
+    EVENT_DEBUG("Updating timer %d timeout with %d ms freq", timer, frequency);
+    if (gettimeofday(&tv, NULL) < 0) {
+        return;
+    }
+
+    for (i = 0 ; i < eventLoop.timeoutsCount ; i++) {
+        if (eventLoop.timeouts[i].timer == timer) {
+            eventLoop.timeouts[i].frequency = frequency;
+            eventLoop.timeouts[i].expiresAt =
+                frequency >= 0 ? frequency +
+                (((unsigned long long)tv.tv_sec)*1000) +
+                (((unsigned long long)tv.tv_usec)/1000) : 0;
+        }
+    }
 }
 
 /*
@@ -175,6 +205,7 @@ int virEventAddTimeoutImpl(int timeout, 
  */
 int virEventRemoveTimeoutImpl(int timer) {
     int i;
+    EVENT_DEBUG("Remove timer %d", timer);
     for (i = 0 ; i < eventLoop.timeoutsCount ; i++) {
         if (eventLoop.timeouts[i].deleted)
             continue;
@@ -196,13 +227,13 @@ static int virEventCalculateTimeout(int 
 static int virEventCalculateTimeout(int *timeout) {
     unsigned long long then = 0;
     int i;
-
+    EVENT_DEBUG("Calculate expiry of %d timers", eventLoop.timeoutsCount);
     /* Figure out if we need a timeout */
     for (i = 0 ; i < eventLoop.timeoutsCount ; i++) {
-        if (eventLoop.timeouts[i].deleted)
-            continue;
-
-        qemudDebug("Got a timeout scheduled for %llu", eventLoop.timeouts[i].expiresAt);
+        if (eventLoop.timeouts[i].deleted || eventLoop.timeouts[i].frequency < 0)
+            continue;
+
+        EVENT_DEBUG("Got a timeout scheduled for %llu", eventLoop.timeouts[i].expiresAt);
         if (then == 0 ||
             eventLoop.timeouts[i].expiresAt < then)
             then = eventLoop.timeouts[i].expiresAt;
@@ -220,13 +251,13 @@ static int virEventCalculateTimeout(int 
             ((((unsigned long long)tv.tv_sec)*1000) +
              (((unsigned long long)tv.tv_usec)/1000));
 
-        qemudDebug("Timeout at %llu due in %d ms", then, *timeout);
         if (*timeout < 0)
-            *timeout = 1;
+            *timeout = 0;
     } else {
-        qemudDebug("No timeout due");
         *timeout = -1;
     }
+
+    EVENT_DEBUG("Timeout at %llu due in %d ms", then, *timeout);
 
     return 0;
 }
@@ -256,7 +287,7 @@ static int virEventMakePollFDs(struct po
         fds[nfds].fd = eventLoop.handles[i].fd;
         fds[nfds].events = eventLoop.handles[i].events;
         fds[nfds].revents = 0;
-        qemudDebug("Wait for %d %d\n", eventLoop.handles[i].fd, eventLoop.handles[i].events);
+        //EVENT_DEBUG("Wait for %d %d", eventLoop.handles[i].fd, eventLoop.handles[i].events);
         nfds++;
     }
 
@@ -291,14 +322,14 @@ static int virEventDispatchTimeouts(void
         (((unsigned long long)tv.tv_usec)/1000);
 
     for (i = 0 ; i < ntimeouts ; i++) {
-        if (eventLoop.timeouts[i].deleted)
+        if (eventLoop.timeouts[i].deleted || eventLoop.timeouts[i].frequency < 0)
             continue;
 
         if (eventLoop.timeouts[i].expiresAt <= now) {
             (eventLoop.timeouts[i].cb)(eventLoop.timeouts[i].timer,
                                        eventLoop.timeouts[i].opaque);
             eventLoop.timeouts[i].expiresAt =
-                now + eventLoop.timeouts[i].timeout;
+                now + eventLoop.timeouts[i].frequency;
         }
     }
     return 0;
@@ -322,12 +353,12 @@ static int virEventDispatchHandles(struc
 
     for (i = 0 ; i < nhandles ; i++) {
         if (eventLoop.handles[i].deleted) {
-            qemudDebug("Skip deleted %d\n", eventLoop.handles[i].fd);
+            EVENT_DEBUG("Skip deleted %d", eventLoop.handles[i].fd);
             continue;
         }
 
         if (fds[i].revents) {
-            qemudDebug("Dispatch %d %d %p\n", fds[i].fd, fds[i].revents, eventLoop.handles[i].opaque);
+            EVENT_DEBUG("Dispatch %d %d %p", fds[i].fd, fds[i].revents, eventLoop.handles[i].opaque);
             (eventLoop.handles[i].cb)(fds[i].fd, fds[i].revents,
                                       eventLoop.handles[i].opaque);
         }
@@ -353,7 +384,7 @@ static int virEventCleanupTimeouts(void)
             continue;
         }
 
-        qemudDebug("Purging timeout %d with id %d", i, eventLoop.timeouts[i].timer);
+        EVENT_DEBUG("Purging timeout %d with id %d", i, eventLoop.timeouts[i].timer);
         if ((i+1) < eventLoop.timeoutsCount) {
             memmove(eventLoop.timeouts+i,
                     eventLoop.timeouts+i+1,
@@ -365,7 +396,7 @@ static int virEventCleanupTimeouts(void)
     /* Release some memory if we've got a big chunk free */
     if ((eventLoop.timeoutsAlloc - EVENT_ALLOC_EXTENT) > eventLoop.timeoutsCount) {
         struct virEventTimeout *tmp;
-        qemudDebug("Releasing %d out of %d timeout slots used, releasing %d\n",
+        EVENT_DEBUG("Releasing %d out of %d timeout slots used, releasing %d",
                    eventLoop.timeoutsCount, eventLoop.timeoutsAlloc, EVENT_ALLOC_EXTENT);
         tmp = realloc(eventLoop.timeouts,
                       sizeof(struct virEventTimeout) *
@@ -406,7 +437,7 @@ static int virEventCleanupHandles(void) 
     /* Release some memory if we've got a big chunk free */
     if ((eventLoop.handlesAlloc - EVENT_ALLOC_EXTENT) > eventLoop.handlesCount) {
         struct virEventHandle *tmp;
-        qemudDebug("Releasing %d out of %d handles slots used, releasing %d\n",
+        EVENT_DEBUG("Releasing %d out of %d handles slots used, releasing %d",
                    eventLoop.handlesCount, eventLoop.handlesAlloc, EVENT_ALLOC_EXTENT);
         tmp = realloc(eventLoop.handles,
                       sizeof(struct virEventHandle) *
@@ -437,9 +468,9 @@ int virEventRunOnce(void) {
     }
 
  retry:
-    qemudDebug("Poll on %d handles %p timeout %d\n", nfds, fds, timeout);
+    EVENT_DEBUG("Poll on %d handles %p timeout %d", nfds, fds, timeout);
     ret = poll(fds, nfds, timeout);
-    qemudDebug("Poll got %d event\n", ret);
+    EVENT_DEBUG("Poll got %d event", ret);
     if (ret < 0) {
         if (errno == EINTR) {
             goto retry;
diff -r 0f29c3c9425f qemud/event.h
--- a/qemud/event.h	Mon Sep 17 05:23:04 2007 -0400
+++ b/qemud/event.h	Mon Sep 17 13:29:46 2007 -0400
@@ -39,6 +39,16 @@ int virEventAddHandleImpl(int fd, int ev
 int virEventAddHandleImpl(int fd, int events, virEventHandleCallback cb, void *opaque);
 
 /**
+ * virEventUpdateHandleImpl: change event set for a monitored file handle
+ *
+ * @fd: file handle to monitor for events
+ * @events: bitset of events to wach from POLLnnn constants
+ *
+ * Will not fail if fd exists
+ */
+void virEventUpdateHandleImpl(int fd, int events);
+
+/**
  * virEventRemoveHandleImpl: unregister a callback from a file handle
  *
  * @fd: file handle to stop monitoring for events
@@ -50,14 +60,30 @@ int virEventRemoveHandleImpl(int fd);
 /**
  * virEventAddTimeoutImpl: register a callback for a timer event
  *
- * @timeout: timeout between events in milliseconds
+ * @frequency: time between events in milliseconds
  * @cb: callback to invoke when an event occurrs
  * @opaque: user data to pass to callback
+ *
+ * Setting frequency to -1 will disable the timer. Setting the frequency
+ * to zero will cause it to fire on every event loop iteration.
  *
  * returns -1 if the file handle cannot be registered, a positive
  * integer timer id upon success
  */
-int virEventAddTimeoutImpl(int timeout, virEventTimeoutCallback cb, void *opaque);
+int virEventAddTimeoutImpl(int frequency, virEventTimeoutCallback cb, void *opaque);
+
+/**
+ * virEventUpdateTimeoutImpl: change frequency for a timer
+ *
+ * @timer: timer id to change
+ * @frequency: time between events in milliseconds
+ *
+ * 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 virEventUpdateTimeoutImpl(int timer, int frequency);
 
 /**
  * virEventRemoveTimeoutImpl: unregister a callback for a timer
diff -r 0f29c3c9425f qemud/qemud.c
--- a/qemud/qemud.c	Mon Sep 17 05:23:04 2007 -0400
+++ b/qemud/qemud.c	Mon Sep 17 13:29:46 2007 -0400
@@ -688,8 +688,10 @@ static struct qemud_server *qemudInitial
         goto cleanup;
 
     __virEventRegisterImpl(virEventAddHandleImpl,
+                           virEventUpdateHandleImpl,
                            virEventRemoveHandleImpl,
                            virEventAddTimeoutImpl,
+                           virEventUpdateTimeoutImpl,
                            virEventRemoveTimeoutImpl);
 
     virStateInitialize();
diff -r 0f29c3c9425f src/event.c
--- a/src/event.c	Mon Sep 17 05:23:04 2007 -0400
+++ b/src/event.c	Mon Sep 17 13:29:46 2007 -0400
@@ -27,8 +27,10 @@
 #include <stdlib.h>
 
 static virEventAddHandleFunc addHandleImpl = NULL;
+static virEventUpdateHandleFunc updateHandleImpl = NULL;
 static virEventRemoveHandleFunc removeHandleImpl = NULL;
 static virEventAddTimeoutFunc addTimeoutImpl = NULL;
+static virEventUpdateTimeoutFunc updateTimeoutImpl = NULL;
 static virEventRemoveTimeoutFunc removeTimeoutImpl = NULL;
 
 int virEventAddHandle(int fd, int events, virEventHandleCallback cb, void *opaque) {
@@ -36,6 +38,10 @@ int virEventAddHandle(int fd, int events
         return -1;
 
     return addHandleImpl(fd, events, cb, opaque);
+}
+
+void virEventUpdateHandle(int fd, int events) {
+    updateHandleImpl(fd, events);
 }
 
 int virEventRemoveHandle(int fd) {
@@ -52,6 +58,10 @@ int virEventAddTimeout(int timeout, virE
     return addTimeoutImpl(timeout, cb, opaque);
 }
 
+void virEventUpdateTimeout(int timer, int timeout) {
+    updateTimeoutImpl(timer, timeout);
+}
+
 int virEventRemoveTimeout(int timer) {
     if (!removeTimeoutImpl)
         return -1;
@@ -60,12 +70,16 @@ int virEventRemoveTimeout(int timer) {
 }
 
 void __virEventRegisterImpl(virEventAddHandleFunc addHandle,
-                           virEventRemoveHandleFunc removeHandle,
-                           virEventAddTimeoutFunc addTimeout,
-                           virEventRemoveTimeoutFunc removeTimeout) {
+                            virEventUpdateHandleFunc updateHandle,
+                            virEventRemoveHandleFunc removeHandle,
+                            virEventAddTimeoutFunc addTimeout,
+                            virEventUpdateTimeoutFunc updateTimeout,
+                            virEventRemoveTimeoutFunc removeTimeout) {
     addHandleImpl = addHandle;
+    updateHandleImpl = updateHandle;
     removeHandleImpl = removeHandle;
     addTimeoutImpl = addTimeout;
+    updateTimeoutImpl = updateTimeout;
     removeTimeoutImpl = removeTimeout;
 }
 
diff -r 0f29c3c9425f src/event.h
--- a/src/event.h	Mon Sep 17 05:23:04 2007 -0400
+++ b/src/event.h	Mon Sep 17 13:29:46 2007 -0400
@@ -47,6 +47,16 @@ int virEventAddHandle(int fd, int events
 int virEventAddHandle(int fd, int events, virEventHandleCallback cb, void *opaque);
 
 /**
+ * virEventUpdateHandle: change event set for a monitored file handle
+ *
+ * @fd: file handle to monitor for events
+ * @events: bitset of events to wach from POLLnnn constants
+ *
+ * Will not fail if fd exists
+ */
+void virEventUpdateHandle(int fd, int events);
+
+/**
  * virEventRemoveHandle: unregister a callback from a file handle
  *
  * @fd: file handle to stop monitoring for events
@@ -66,14 +76,30 @@ typedef void (*virEventTimeoutCallback)(
 /**
  * virEventAddTimeout: register a callback for a timer event
  *
- * @timeout: timeout between events in milliseconds
+ * @frequency: time between events in milliseconds
  * @cb: callback to invoke when an event occurrs
  * @opaque: user data to pass to callback
+ *
+ * Setting frequency to -1 will disable the timer. Setting the frequency
+ * to zero will cause it to fire on every event loop iteration.
  *
  * returns -1 if the file handle cannot be registered, a positive
  * integer timer id upon success
  */
-int virEventAddTimeout(int timeout, virEventTimeoutCallback cb, void *opaque);
+int virEventAddTimeout(int frequency, virEventTimeoutCallback cb, void *opaque);
+
+/**
+ * virEventUpdateTimeoutImpl: change frequency for a timer
+ *
+ * @timer: timer id to change
+ * @frequency: time between events in milliseconds
+ *
+ * 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 frequency);
 
 /**
  * virEventRemoveTimeout: unregister a callback for a timer
@@ -85,14 +111,18 @@ int virEventRemoveTimeout(int timer);
 int virEventRemoveTimeout(int timer);
 
 typedef int (*virEventAddHandleFunc)(int, int, virEventHandleCallback, void *);
+typedef void (*virEventUpdateHandleFunc)(int, int);
 typedef int (*virEventRemoveHandleFunc)(int);
 
 typedef int (*virEventAddTimeoutFunc)(int, virEventTimeoutCallback, void *);
+typedef void (*virEventUpdateTimeoutFunc)(int, int);
 typedef int (*virEventRemoveTimeoutFunc)(int);
 
 void __virEventRegisterImpl(virEventAddHandleFunc addHandle,
+			    virEventUpdateHandleFunc updateHandle,
 			    virEventRemoveHandleFunc removeHandle,
 			    virEventAddTimeoutFunc addTimeout,
+			    virEventUpdateTimeoutFunc updateTimeout,
 			    virEventRemoveTimeoutFunc removeTimeout);
 
 #define virEventRegisterImpl(ah,rh,at,rt) __virEventRegisterImpl(ah,rh,at,rt)

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