tvl-depot/absl/flags/internal/flag.cc
Abseil Team 83c1d65c90 Export of internal Abseil changes
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972333fe1e43427849b8a634aa35061e81be3642 by Abseil Team <absl-team@google.com>:

Replace deprecated thread annotations macros.

PiperOrigin-RevId: 267332619

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7039c6dc499a31c372b4872eda0772455931c360 by Gennadiy Rozental <rogeeff@google.com>:

Internal change

PiperOrigin-RevId: 267220271

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a3f524d2afc2535686f206a7ce06961016349d7a by Abseil Team <absl-team@google.com>:

Factor kernel_timeout out of synchronization.

PiperOrigin-RevId: 267217304

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90287de4114ef9a06cafe50256a2d03349772c21 by Abseil Team <absl-team@google.com>:

Fixed comment typo.

PiperOrigin-RevId: 267198532

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d312c1a1e52aeca1871ff0deead416d09a7f237e by Gennadiy Rozental <rogeeff@google.com>:

Internal change

PiperOrigin-RevId: 267185804
GitOrigin-RevId: 972333fe1e43427849b8a634aa35061e81be3642
Change-Id: Ia8a2f877c57cef9854aad48f1753af872fc04dc8
2019-09-05 06:05:17 -04:00

51 lines
1.9 KiB
C++

//
// Copyright 2019 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
//
// https://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/flags/internal/flag.h"
#include "absl/synchronization/mutex.h"
namespace absl {
namespace flags_internal {
// If the flag has a mutation callback this function invokes it. While the
// callback is being invoked the primary flag's mutex is unlocked and it is
// re-locked back after call to callback is completed. Callback invocation is
// guarded by flag's secondary mutex instead which prevents concurrent
// callback invocation. Note that it is possible for other thread to grab the
// primary lock and update flag's value at any time during the callback
// invocation. This is by design. Callback can get a value of the flag if
// necessary, but it might be different from the value initiated the callback
// and it also can be different by the time the callback invocation is
// completed. Requires that *primary_lock be held in exclusive mode; it may be
// released and reacquired by the implementation.
void InvokeCallback(absl::Mutex* primary_mu, absl::Mutex* callback_mu,
FlagCallback cb) ABSL_EXCLUSIVE_LOCKS_REQUIRED(primary_mu) {
if (!cb) return;
// When executing the callback we need the primary flag's mutex to be
// unlocked so that callback can retrieve the flag's value.
primary_mu->Unlock();
{
absl::MutexLock lock(callback_mu);
cb();
}
primary_mu->Lock();
}
} // namespace flags_internal
} // namespace absl