tor-browser

The Tor Browser
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MsaaIdGenerator.cpp (2680B)

      1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
      2 /* vim: set ts=2 et sw=2 tw=80: */
      3 /* This Source Code Form is subject to the terms of the Mozilla Public
      4 * License, v. 2.0. If a copy of the MPL was not distributed with this
      5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
      6 
      7 #include "MsaaIdGenerator.h"
      8 
      9 #include "mozilla/Assertions.h"
     10 #include "mozilla/ClearOnShutdown.h"
     11 #include "MsaaAccessible.h"
     12 #include "nsAccessibilityService.h"
     13 
     14 namespace mozilla {
     15 namespace a11y {
     16 
     17 uint32_t MsaaIdGenerator::GetID() {
     18  if (!mGetIDCalled) {
     19    mGetIDCalled = true;
     20    // this is a static instance, so capturing this here is safe.
     21    RunOnShutdown([this] {
     22      if (mReleaseIDTimer) {
     23        mReleaseIDTimer->Cancel();
     24        ReleasePendingIDs();
     25      }
     26    });
     27  }
     28  uint32_t id = mIDSet.GetID();
     29  MOZ_ASSERT(id <= ((1UL << kNumFullIDBits) - 1UL));
     30  return ~id;
     31 }
     32 
     33 void MsaaIdGenerator::ReleasePendingIDs() {
     34  for (auto id : mIDsToRelease) {
     35    mIDSet.ReleaseID(~id);
     36  }
     37  mIDsToRelease.Clear();
     38  mReleaseIDTimer = nullptr;
     39 }
     40 
     41 void MsaaIdGenerator::ReleasePendingIdsCallback(nsITimer* aTimer,
     42                                                void* aClosure) {
     43  MsaaIdGenerator* gen = (MsaaIdGenerator*)aClosure;
     44  gen->ReleasePendingIDs();
     45 }
     46 
     47 bool MsaaIdGenerator::ReleaseID(uint32_t aID) {
     48  MOZ_ASSERT(aID != MsaaAccessible::kNoID);
     49  // Releasing an id means it can be reused. Reusing ids too quickly can
     50  // cause problems for clients which process events asynchronously.
     51  // Therefore, we release ids after a short delay. This doesn't seem to be
     52  // necessary when the cache is disabled, perhaps because the COM runtime
     53  // holds references to our objects for longer.
     54  if (nsAccessibilityService::IsShutdown()) {
     55    // If accessibility is shut down, no more Accessibles will be created.
     56    // Also, if the service is shut down, it's possible XPCOM is also shutting
     57    // down, in which case timers won't work. Thus, we release the id
     58    // immediately.
     59    mIDSet.ReleaseID(~aID);
     60    return true;
     61  }
     62  const uint32_t kReleaseDelay = 1000;
     63  mIDsToRelease.AppendElement(aID);
     64  if (!mReleaseIDTimer) {
     65    mReleaseIDTimer = NS_NewTimer();
     66  }
     67  // mReleaseIDTimer is cancelled on shutdown and this is a static instance,
     68  // so capturing this here is safe.
     69  mReleaseIDTimer->InitWithNamedFuncCallback(
     70      ReleasePendingIdsCallback, this, kReleaseDelay, nsITimer::TYPE_ONE_SHOT,
     71      "a11y::MsaaIdGenerator::ReleaseIDDelayed"_ns);
     72 
     73  return true;
     74 }
     75 
     76 void MsaaIdGenerator::ReleaseID(NotNull<MsaaAccessible*> aMsaaAcc) {
     77  ReleaseID(aMsaaAcc->GetExistingID());
     78 }
     79 
     80 }  // namespace a11y
     81 }  // namespace mozilla