+/******************************************************************************
+ *
+ * Copyright (C) 2014 Google, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ ******************************************************************************/
+
#pragma once
+#include <stdbool.h>
+
struct semaphore_t;
typedef struct semaphore_t semaphore_t;
+// Creates a new semaphore with an initial value of |value|.
+// Returns NULL on failure. The returned object must be released
+// with |semaphore_free|.
semaphore_t *semaphore_new(unsigned int value);
+
+// Frees a semaphore allocated with |semaphore_new|. |semaphore| may
+// be NULL.
void semaphore_free(semaphore_t *semaphore);
+// Decrements the value of |semaphore|. If it is 0, this call blocks until
+// it becomes non-zero. |semaphore| may not be NULL.
void semaphore_wait(semaphore_t *semaphore);
+
+// Tries to decrement the value of |semaphore|. Returns true if the value was
+// decremented, false if the value was 0. This function never blocks. |semaphore|
+// may not be NULL.
+bool semaphore_try_wait(semaphore_t *semaphore);
+
+// Increments the value of |semaphore|. |semaphore| may not be NULL.
void semaphore_post(semaphore_t *semaphore);
+/******************************************************************************
+ *
+ * Copyright (C) 2014 Google, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ ******************************************************************************/
+
#define LOG_TAG "osi_semaphore"
#include <assert.h>
#include <errno.h>
+#include <fcntl.h>
#include <string.h>
#include <sys/eventfd.h>
#include <utils/Log.h>
ALOGE("%s unable to wait on semaphore: %s", __func__, strerror(errno));
}
+bool semaphore_try_wait(semaphore_t *semaphore) {
+ assert(semaphore != NULL);
+ assert(semaphore->fd != -1);
+
+ int flags = fcntl(semaphore->fd, F_GETFL);
+ if (flags == -1) {
+ ALOGE("%s unable to get flags for semaphore fd: %s", __func__, strerror(errno));
+ return false;
+ }
+ if (fcntl(semaphore->fd, F_SETFL, flags | O_NONBLOCK) == -1) {
+ ALOGE("%s unable to set O_NONBLOCK for semaphore fd: %s", __func__, strerror(errno));
+ return false;
+ }
+
+ eventfd_t value;
+ if (eventfd_read(semaphore->fd, &value) == -1)
+ return false;
+
+ if (fcntl(semaphore->fd, F_SETFL, flags) == -1)
+ ALOGE("%s unable to resetore flags for semaphore fd: %s", __func__, strerror(errno));
+ return true;
+}
+
void semaphore_post(semaphore_t *semaphore) {
assert(semaphore != NULL);
assert(semaphore->fd != -1);