76 lines
2.3 KiB
C++
76 lines
2.3 KiB
C++
// Licensed to the Apache Software Foundation (ASF) under one
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// or more contributor license agreements. See the NOTICE file
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// distributed with this work for additional information
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// regarding copyright ownership. The ASF licenses this file
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// to you under the Apache License, Version 2.0 (the
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// "License"); you may not use this file except in compliance
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// with the License. You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing,
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// software distributed under the License is distributed on an
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// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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// KIND, either express or implied. See the License for the
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// specific language governing permissions and limitations
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// under the License.
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// bthread - A M:N threading library to make applications more concurrent.
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// Date: 2017/07/27 23:07:06
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#ifndef BTHREAD_PARKING_LOT_H
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#define BTHREAD_PARKING_LOT_H
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#include "butil/atomicops.h"
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#include "bthread/sys_futex.h"
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namespace bthread {
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// Park idle workers.
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class BAIDU_CACHELINE_ALIGNMENT ParkingLot {
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public:
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class State {
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public:
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State(): val(0) {}
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bool stopped() const { return val & 1; }
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private:
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friend class ParkingLot;
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State(int val) : val(val) {}
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int val;
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};
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ParkingLot() : _pending_signal(0) {}
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// Wake up at most `num_task' workers.
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// Returns #workers woken up.
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int signal(int num_task) {
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_pending_signal.fetch_add((num_task << 1), butil::memory_order_release);
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return futex_wake_private(&_pending_signal, num_task);
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}
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// Get a state for later wait().
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State get_state() {
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return _pending_signal.load(butil::memory_order_acquire);
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}
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// Wait for tasks.
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// If the `expected_state' does not match, wait() may finish directly.
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void wait(const State& expected_state) {
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futex_wait_private(&_pending_signal, expected_state.val, NULL);
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}
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// Wakeup suspended wait() and make them unwaitable ever.
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void stop() {
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_pending_signal.fetch_or(1);
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futex_wake_private(&_pending_signal, 10000);
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}
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private:
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// higher 31 bits for signalling, LSB for stopping.
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butil::atomic<int> _pending_signal;
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};
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} // namespace bthread
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#endif // BTHREAD_PARKING_LOT_H
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