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[netatalk.git] / libevent / changelist-internal.h

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+/*
+ * Copyright (c) 2009-2012 Niels Provos and Nick Mathewson
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+#ifndef _CHANGELIST_H_
+#define _CHANGELIST_H_
+
+/*
+  A "changelist" is a list of all the fd status changes that should be made
+  between calls to the backend's dispatch function.  There are a few reasons
+  that a backend would want to queue changes like this rather than processing
+  them immediately.
+
+    1) Sometimes applications will add and delete the same event more than
+       once between calls to dispatch.  Processing these changes immediately
+       is needless, and potentially expensive (especially if we're on a system
+       that makes one syscall per changed event).
+
+    2) Sometimes we can coalesce multiple changes on the same fd into a single
+       syscall if we know about them in advance.  For example, epoll can do an
+       add and a delete at the same time, but only if we have found out about
+       both of them before we tell epoll.
+
+    3) Sometimes adding an event that we immediately delete can cause
+       unintended consequences: in kqueue, this makes pending events get
+       reported spuriously.
+ */
+
+#include "event2/util.h"
+
+/** Represents a */
+struct event_change {
+       /** The fd or signal whose events are to be changed */
+       evutil_socket_t fd;
+       /* The events that were enabled on the fd before any of these changes
+          were made.  May include EV_READ or EV_WRITE. */
+       short old_events;
+
+       /* The changes that we want to make in reading and writing on this fd.
+        * If this is a signal, then read_change has EV_CHANGE_SIGNAL set,
+        * and write_change is unused. */
+       ev_uint8_t read_change;
+       ev_uint8_t write_change;
+};
+
+/* Flags for read_change and write_change. */
+
+/* If set, add the event. */
+#define EV_CHANGE_ADD     0x01
+/* If set, delete the event.  Exclusive with EV_CHANGE_ADD */
+#define EV_CHANGE_DEL     0x02
+/* If set, this event refers a signal, not an fd. */
+#define EV_CHANGE_SIGNAL  EV_SIGNAL
+/* Set for persistent events.  Currently not used. */
+#define EV_CHANGE_PERSIST EV_PERSIST
+/* Set for adding edge-triggered events. */
+#define EV_CHANGE_ET      EV_ET
+
+/* The value of fdinfo_size that a backend should use if it is letting
+ * changelist handle its add and delete functions. */
+#define EVENT_CHANGELIST_FDINFO_SIZE sizeof(int)
+
+/** Set up the data fields in a changelist. */
+void event_changelist_init(struct event_changelist *changelist);
+/** Remove every change in the changelist, and make corresponding changes
+ * in the event maps in the base.  This function is generally used right
+ * after making all the changes in the changelist. */
+void event_changelist_remove_all(struct event_changelist *changelist,
+    struct event_base *base);
+/** Free all memory held in a changelist. */
+void event_changelist_freemem(struct event_changelist *changelist);
+
+/** Implementation of eventop_add that queues the event in a changelist. */
+int event_changelist_add(struct event_base *base, evutil_socket_t fd, short old, short events,
+    void *p);
+/** Implementation of eventop_del that queues the event in a changelist. */
+int event_changelist_del(struct event_base *base, evutil_socket_t fd, short old, short events,
+    void *p);
+
+#endif