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// Copyright 2021 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "content/common/process_visibility_tracker.h"
#include "base/no_destructor.h"
namespace content {
// static
ProcessVisibilityTracker* ProcessVisibilityTracker::GetInstance() {
static base::NoDestructor<ProcessVisibilityTracker> instance;
return instance.get();
}
ProcessVisibilityTracker::ProcessVisibilityTracker()
: observers_(base::MakeRefCounted<
base::ObserverListThreadSafe<ProcessVisibilityObserver>>()) {}
ProcessVisibilityTracker::~ProcessVisibilityTracker() {
DCHECK_CALLED_ON_VALID_SEQUENCE(main_thread_);
}
void ProcessVisibilityTracker::AddObserver(
ProcessVisibilityObserver* observer) {
std::optional<bool> is_visible;
{
// Synchronize access to |observers_| and |is_visible_| to ensure
// consistency in notifications to observers (in case of concurrent
// modification of the visibility state).
base::AutoLock lock(lock_);
observers_->AddObserver(observer);
is_visible = is_visible_;
}
// Notify outside the lock to allow the observer to call back into
// ProcessVisibilityTracker.
if (is_visible.has_value())
observer->OnVisibilityChanged(*is_visible);
}
void ProcessVisibilityTracker::RemoveObserver(
ProcessVisibilityObserver* observer) {
base::AutoLock lock(lock_);
observers_->RemoveObserver(observer);
}
void ProcessVisibilityTracker::OnProcessVisibilityChanged(bool visible) {
DCHECK_CALLED_ON_VALID_SEQUENCE(main_thread_);
{
base::AutoLock lock(lock_);
if (is_visible_.has_value() && *is_visible_ == visible)
return;
is_visible_ = visible;
observers_->Notify(
FROM_HERE, &ProcessVisibilityObserver::OnVisibilityChanged, visible);
}
}
} // namespace content
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