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authorGravatar misterg <misterg@google.com>2017-09-19 16:54:40 -0400
committerGravatar misterg <misterg@google.com>2017-09-19 16:54:40 -0400
commitc2e754829628d1e9b7a16b3389cfdace76950fdf (patch)
tree5a7f056f44e27c30e10025113b644f0b3b5801fc /absl/synchronization/barrier.cc
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+// Copyright 2017 The Abseil Authors.
+//
+// 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.
+
+#include "absl/synchronization/barrier.h"
+
+#include "absl/base/internal/raw_logging.h"
+#include "absl/synchronization/mutex.h"
+
+namespace absl {
+
+// Return whether int *arg is zero.
+static bool IsZero(void *arg) {
+ return 0 == *reinterpret_cast<int *>(arg);
+}
+
+bool Barrier::Block() {
+ MutexLock l(&this->lock_);
+
+ this->num_to_block_--;
+ if (this->num_to_block_ < 0) {
+ ABSL_RAW_LOG(
+ FATAL,
+ "Block() called too many times. num_to_block_=%d out of total=%d",
+ this->num_to_block_, this->num_to_exit_);
+ }
+
+ this->lock_.Await(Condition(IsZero, &this->num_to_block_));
+
+ // Determine which thread can safely delete this Barrier object
+ this->num_to_exit_--;
+ ABSL_RAW_CHECK(this->num_to_exit_ >= 0, "barrier underflow");
+
+ // If num_to_exit_ == 0 then all other threads in the barrier have
+ // exited the Wait() and have released the Mutex so this thread is
+ // free to delete the barrier.
+ return this->num_to_exit_ == 0;
+}
+
+} // namespace absl