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-rw-r--r--zbar/processor/lock.c228
1 files changed, 228 insertions, 0 deletions
diff --git a/zbar/processor/lock.c b/zbar/processor/lock.c
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+/*------------------------------------------------------------------------
+ * Copyright 2007-2009 (c) Jeff Brown <spadix@users.sourceforge.net>
+ *
+ * This file is part of the ZBar Bar Code Reader.
+ *
+ * The ZBar Bar Code Reader is free software; you can redistribute it
+ * and/or modify it under the terms of the GNU Lesser Public License as
+ * published by the Free Software Foundation; either version 2.1 of
+ * the License, or (at your option) any later version.
+ *
+ * The ZBar Bar Code Reader 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 Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser Public License
+ * along with the ZBar Bar Code Reader; if not, write to the Free
+ * Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301 USA
+ *
+ * http://sourceforge.net/projects/zbar
+ *------------------------------------------------------------------------*/
+
+#include <assert.h>
+#include "processor.h"
+
+/* the processor api lock is a recursive mutex with added capabilities
+ * to completely drop all lock levels before blocking and atomically
+ * unblock a waiting set. the lock is implemented using a variation
+ * of the "specific notification pattern" [cargill], which makes it
+ * easy to provide these features across platforms with consistent,
+ * predictable semantics. probably overkill, but additional overhead
+ * associated with this mechanism should fall in the noise, as locks
+ * are only exchanged O(frame/image)
+ *
+ * [cargill]
+ * http://www.profcon.com/profcon/cargill/jgf/9809/SpecificNotification.html
+ */
+
+static inline proc_waiter_t *proc_waiter_queue(zbar_processor_t *proc)
+{
+ proc_waiter_t *waiter = proc->free_waiter;
+ if (waiter) {
+ proc->free_waiter = waiter->next;
+ waiter->events = 0;
+ } else {
+ waiter = calloc(1, sizeof(proc_waiter_t));
+ _zbar_event_init(&waiter->notify);
+ }
+
+ waiter->next = NULL;
+ waiter->requester = _zbar_thread_self();
+
+ if (proc->wait_head)
+ proc->wait_tail->next = waiter;
+ else
+ proc->wait_head = waiter;
+ proc->wait_tail = waiter;
+ return (waiter);
+}
+
+static inline proc_waiter_t *proc_waiter_dequeue(zbar_processor_t *proc)
+{
+ proc_waiter_t *prev = proc->wait_next, *waiter;
+ if (prev)
+ waiter = prev->next;
+ else
+ waiter = proc->wait_head;
+ while (waiter && (waiter->events & EVENTS_PENDING)) {
+ prev = waiter;
+ proc->wait_next = waiter;
+ waiter = waiter->next;
+ }
+
+ if (waiter) {
+ if (prev)
+ prev->next = waiter->next;
+ else
+ proc->wait_head = waiter->next;
+ if (!waiter->next)
+ proc->wait_tail = prev;
+ waiter->next = NULL;
+
+ proc->lock_level = 1;
+ proc->lock_owner = waiter->requester;
+ }
+ return (waiter);
+}
+
+static inline void proc_waiter_release(zbar_processor_t *proc,
+ proc_waiter_t *waiter)
+{
+ if (waiter) {
+ waiter->next = proc->free_waiter;
+ proc->free_waiter = waiter;
+ }
+}
+
+int _zbar_processor_lock(zbar_processor_t *proc)
+{
+ proc_waiter_t *waiter;
+ if (!proc->lock_level) {
+ proc->lock_owner = _zbar_thread_self();
+ proc->lock_level = 1;
+ return (0);
+ }
+
+ if (_zbar_thread_is_self(proc->lock_owner)) {
+ proc->lock_level++;
+ return (0);
+ }
+
+ waiter = proc_waiter_queue(proc);
+ _zbar_event_wait(&waiter->notify, &proc->mutex, NULL);
+
+ assert(proc->lock_level == 1);
+ assert(_zbar_thread_is_self(proc->lock_owner));
+
+ proc_waiter_release(proc, waiter);
+ return (0);
+}
+
+int _zbar_processor_unlock(zbar_processor_t *proc, int all)
+{
+ assert(proc->lock_level > 0);
+ assert(_zbar_thread_is_self(proc->lock_owner));
+
+ if (all)
+ proc->lock_level = 0;
+ else
+ proc->lock_level--;
+
+ if (!proc->lock_level) {
+ proc_waiter_t *waiter = proc_waiter_dequeue(proc);
+ if (waiter)
+ _zbar_event_trigger(&waiter->notify);
+ }
+ return (0);
+}
+
+void _zbar_processor_notify(zbar_processor_t *proc, unsigned events)
+{
+ proc_waiter_t *waiter;
+ proc->wait_next = NULL;
+ for (waiter = proc->wait_head; waiter; waiter = waiter->next)
+ waiter->events =
+ ((waiter->events & ~events) | (events & EVENT_CANCELED));
+
+ if (!proc->lock_level) {
+ waiter = proc_waiter_dequeue(proc);
+ if (waiter)
+ _zbar_event_trigger(&waiter->notify);
+ }
+}
+
+static inline int proc_wait_unthreaded(zbar_processor_t *proc,
+ proc_waiter_t *waiter,
+ zbar_timer_t *timeout)
+{
+ int rc;
+ int blocking = proc->streaming && zbar_video_get_fd(proc->video) < 0;
+ _zbar_mutex_unlock(&proc->mutex);
+
+ rc = 1;
+ while (rc > 0 && (waiter->events & EVENTS_PENDING)) {
+ int reltime;
+ /* FIXME lax w/the locking (though shouldn't matter...) */
+ if (blocking) {
+ zbar_image_t *img = zbar_video_next_image(proc->video);
+ if (!img) {
+ rc = -1;
+ break;
+ }
+
+ /* FIXME reacquire API lock! (refactor w/video thread?) */
+ _zbar_mutex_lock(&proc->mutex);
+ _zbar_process_image(proc, img);
+ zbar_image_destroy(img);
+ _zbar_mutex_unlock(&proc->mutex);
+ }
+ reltime = _zbar_timer_check(timeout);
+ if (blocking && (reltime < 0 || reltime > MAX_INPUT_BLOCK))
+ reltime = MAX_INPUT_BLOCK;
+ rc = _zbar_processor_input_wait(proc, NULL, reltime);
+ }
+ _zbar_mutex_lock(&proc->mutex);
+ return (rc);
+}
+
+int _zbar_processor_wait(zbar_processor_t *proc, unsigned events,
+ zbar_timer_t *timeout)
+{
+ int save_level;
+ proc_waiter_t *waiter;
+ int rc;
+
+ _zbar_mutex_lock(&proc->mutex);
+ save_level = proc->lock_level;
+ waiter = proc_waiter_queue(proc);
+ waiter->events = events & EVENTS_PENDING;
+
+ _zbar_processor_unlock(proc, 1);
+ if (proc->threaded)
+ rc = _zbar_event_wait(&waiter->notify, &proc->mutex, timeout);
+ else
+ rc = proc_wait_unthreaded(proc, waiter, timeout);
+
+ if (rc <= 0 || !proc->threaded) {
+ /* reacquire api lock */
+ waiter->events &= EVENT_CANCELED;
+ proc->wait_next = NULL;
+ if (!proc->lock_level) {
+ proc_waiter_t *w = proc_waiter_dequeue(proc);
+ assert(w == waiter);
+ } else
+ _zbar_event_wait(&waiter->notify, &proc->mutex, NULL);
+ }
+ if (rc > 0 && (waiter->events & EVENT_CANCELED))
+ rc = -1;
+
+ assert(proc->lock_level == 1);
+ assert(_zbar_thread_is_self(proc->lock_owner));
+
+ proc->lock_level = save_level;
+ proc_waiter_release(proc, waiter);
+ _zbar_mutex_unlock(&proc->mutex);
+ return (rc);
+}
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