1 files changed, 88 insertions, 0 deletions
diff --git a/third_party/libwebrtc/rtc_base/operations_chain.cc b/third_party/libwebrtc/rtc_base/operations_chain.cc
new file mode 100644
index 0000000000..4398bb16c1
--- /dev/null
+++ b/third_party/libwebrtc/rtc_base/operations_chain.cc
@@ -0,0 +1,88 @@
+/*
+ *  Copyright 2019 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "rtc_base/operations_chain.h"
+
+#include "api/make_ref_counted.h"
+#include "rtc_base/checks.h"
+
+namespace rtc {
+
+OperationsChain::CallbackHandle::CallbackHandle(
+    scoped_refptr<OperationsChain> operations_chain)
+    : operations_chain_(std::move(operations_chain)) {}
+
+OperationsChain::CallbackHandle::~CallbackHandle() {
+#if RTC_DCHECK_IS_ON
+  RTC_DCHECK(has_run_);
+#endif
+}
+
+void OperationsChain::CallbackHandle::OnOperationComplete() {
+#if RTC_DCHECK_IS_ON
+  RTC_DCHECK(!has_run_);
+  has_run_ = true;
+#endif  // RTC_DCHECK_IS_ON
+  operations_chain_->OnOperationComplete();
+  // We have no reason to keep the `operations_chain_` alive through reference
+  // counting anymore.
+  operations_chain_ = nullptr;
+}
+
+// static
+scoped_refptr<OperationsChain> OperationsChain::Create() {
+  // Explicit new, to access private constructor.
+  return rtc::scoped_refptr<OperationsChain>(new OperationsChain());
+}
+
+OperationsChain::OperationsChain() {
+  RTC_DCHECK_RUN_ON(&sequence_checker_);
+}
+
+OperationsChain::~OperationsChain() {
+  // Operations keep the chain alive through reference counting so this should
+  // not be possible. The fact that the chain is empty makes it safe to
+  // destroy the OperationsChain on any sequence.
+  RTC_DCHECK(chained_operations_.empty());
+}
+
+void OperationsChain::SetOnChainEmptyCallback(
+    std::function<void()> on_chain_empty_callback) {
+  RTC_DCHECK_RUN_ON(&sequence_checker_);
+  on_chain_empty_callback_ = std::move(on_chain_empty_callback);
+}
+
+bool OperationsChain::IsEmpty() const {
+  RTC_DCHECK_RUN_ON(&sequence_checker_);
+  return chained_operations_.empty();
+}
+
+std::function<void()> OperationsChain::CreateOperationsChainCallback() {
+  return [handle = rtc::make_ref_counted<CallbackHandle>(
+              rtc::scoped_refptr<OperationsChain>(this))]() {
+    handle->OnOperationComplete();
+  };
+}
+
+void OperationsChain::OnOperationComplete() {
+  RTC_DCHECK_RUN_ON(&sequence_checker_);
+  // The front element is the operation that just completed, remove it.
+  RTC_DCHECK(!chained_operations_.empty());
+  chained_operations_.pop();
+  // If there are any other operations chained, execute the next one. Otherwise,
+  // invoke the "on chain empty" callback if it has been set.
+  if (!chained_operations_.empty()) {
+    chained_operations_.front()->Run();
+  } else if (on_chain_empty_callback_.has_value()) {
+    on_chain_empty_callback_.value()();
+  }
+}
+
+}  // namespace rtc