1 | /* Copyright 2019 Google LLC. All Rights Reserved. |
2 | |
3 | Licensed under the Apache License, Version 2.0 (the "License"); |
4 | you may not use this file except in compliance with the License. |
5 | You may obtain a copy of the License at |
6 | |
7 | http://www.apache.org/licenses/LICENSE-2.0 |
8 | |
9 | Unless required by applicable law or agreed to in writing, software |
10 | distributed under the License is distributed on an "AS IS" BASIS, |
11 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
12 | See the License for the specific language governing permissions and |
13 | limitations under the License. |
14 | ==============================================================================*/ |
15 | |
16 | #ifndef RUY_RUY_BLOCKING_COUNTER_H_ |
17 | #define RUY_RUY_BLOCKING_COUNTER_H_ |
18 | |
19 | #include <atomic> |
20 | #include <condition_variable> // NOLINT(build/c++11) // IWYU pragma: keep |
21 | #include <mutex> // NOLINT(build/c++11) // IWYU pragma: keep |
22 | |
23 | #include "ruy/time.h" |
24 | |
25 | namespace ruy { |
26 | |
27 | // A BlockingCounter lets one thread to wait for N events to occur. |
28 | // This is how the master thread waits for all the worker threads |
29 | // to have finished working. |
30 | // The waiting is done using a naive spinlock waiting for the atomic |
31 | // count_ to hit the value 0. This is acceptable because in our usage |
32 | // pattern, BlockingCounter is used only to synchronize threads after |
33 | // short-lived tasks (performing parts of the same GEMM). It is not used |
34 | // for synchronizing longer waits (resuming work on the next GEMM). |
35 | class BlockingCounter { |
36 | public: |
37 | BlockingCounter() : count_(0) {} |
38 | |
39 | // Sets/resets the counter; initial_count is the number of |
40 | // decrementing events that the Wait() call will be waiting for. |
41 | void Reset(int initial_count); |
42 | |
43 | // Decrements the counter; if the counter hits zero, signals |
44 | // the threads that were waiting for that, and returns true. |
45 | // Otherwise (if the decremented count is still nonzero), |
46 | // returns false. |
47 | bool DecrementCount(); |
48 | |
49 | // Waits for the N other threads (N having been set by Reset()) |
50 | // to hit the BlockingCounter. |
51 | // |
52 | // Will first spin-wait for `spin_duration` before reverting to passive wait. |
53 | void Wait(const Duration spin_duration); |
54 | |
55 | private: |
56 | std::atomic<int> count_; |
57 | |
58 | // The condition variable and mutex allowing to passively wait for count_ |
59 | // to reach the value zero, in the case of longer waits. |
60 | std::condition_variable count_cond_; |
61 | std::mutex count_mutex_; |
62 | }; |
63 | |
64 | } // namespace ruy |
65 | |
66 | #endif // RUY_RUY_BLOCKING_COUNTER_H_ |
67 | |