Abseil Common Libraries (C++) (grcp 依赖)
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51 lines
1.9 KiB
51 lines
1.9 KiB
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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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