52 lines
1.9 KiB
C++
52 lines
1.9 KiB
C++
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//
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// Copyright 2019 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://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, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "absl/flags/internal/flag.h"
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#include "absl/synchronization/mutex.h"
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namespace absl {
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namespace flags_internal {
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// If the flag has a mutation callback this function invokes it. While the
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// callback is being invoked the primary flag's mutex is unlocked and it is
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// re-locked back after call to callback is completed. Callback invocation is
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// guarded by flag's secondary mutex instead which prevents concurrent
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// callback invocation. Note that it is possible for other thread to grab the
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// primary lock and update flag's value at any time during the callback
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// invocation. This is by design. Callback can get a value of the flag if
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// necessary, but it might be different from the value initiated the callback
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// and it also can be different by the time the callback invocation is
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// completed. Requires that *primary_lock be held in exclusive mode; it may be
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// released and reacquired by the implementation.
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void InvokeCallback(absl::Mutex* primary_mu, absl::Mutex* callback_mu,
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FlagCallback cb) EXCLUSIVE_LOCKS_REQUIRED(primary_mu) {
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if (!cb) return;
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// When executing the callback we need the primary flag's mutex to be
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// unlocked so that callback can retrieve the flag's value.
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primary_mu->Unlock();
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{
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absl::MutexLock lock(callback_mu);
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cb();
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}
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primary_mu->Lock();
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}
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} // namespace flags_internal
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} // namespace absl
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