Revert of Delete SignalThread class.

webrtc/rtc_base/signalthread.h

Index: webrtc/rtc_base/signalthread.h
diff --git a/webrtc/rtc_base/signalthread.h b/webrtc/rtc_base/signalthread.h
new file mode 100644
index 0000000000000000000000000000000000000000..bc8c98ea7db767a13982825e9b6344096597039e
--- /dev/null
+++ b/webrtc/rtc_base/signalthread.h
@@ -0,0 +1,161 @@
+/*
+ *  Copyright 2004 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.
+ */
+
+#ifndef WEBRTC_RTC_BASE_SIGNALTHREAD_H_
+#define WEBRTC_RTC_BASE_SIGNALTHREAD_H_
+
+#include <string>
+
+#include "webrtc/base/checks.h"
+#include "webrtc/base/constructormagic.h"
+#include "webrtc/base/nullsocketserver.h"
+#include "webrtc/base/sigslot.h"
+#include "webrtc/base/thread.h"
+
+namespace rtc {
+
+///////////////////////////////////////////////////////////////////////////////
+// SignalThread - Base class for worker threads.  The main thread should call
+//  Start() to begin work, and then follow one of these models:
+//   Normal: Wait for SignalWorkDone, and then call Release to destroy.
+//   Cancellation: Call Release(true), to abort the worker thread.
+//   Fire-and-forget: Call Release(false), which allows the thread to run to
+//    completion, and then self-destruct without further notification.
+//   Periodic tasks: Wait for SignalWorkDone, then eventually call Start()
+//    again to repeat the task. When the instance isn't needed anymore,
+//    call Release. DoWork, OnWorkStart and OnWorkStop are called again,
+//    on a new thread.
+//  The subclass should override DoWork() to perform the background task.  By
+//   periodically calling ContinueWork(), it can check for cancellation.
+//   OnWorkStart and OnWorkDone can be overridden to do pre- or post-work
+//   tasks in the context of the main thread.
+///////////////////////////////////////////////////////////////////////////////
+
+class SignalThread
+    : public sigslot::has_slots<>,
+      protected MessageHandler {
+ public:
+  explicit SignalThread(bool use_socket_server = true);
+
+  // Context: Main Thread.  Call before Start to change the worker's name.
+  bool SetName(const std::string& name, const void* obj);
+
+  // Context: Main Thread.  Call to begin the worker thread.
+  void Start();
+
+  // Context: Main Thread.  If the worker thread is not running, deletes the
+  // object immediately.  Otherwise, asks the worker thread to abort processing,
+  // and schedules the object to be deleted once the worker exits.
+  // SignalWorkDone will not be signalled.  If wait is true, does not return
+  // until the thread is deleted.
+  void Destroy(bool wait);
+
+  // Context: Main Thread.  If the worker thread is complete, deletes the
+  // object immediately.  Otherwise, schedules the object to be deleted once
+  // the worker thread completes.  SignalWorkDone will be signalled.
+  void Release();
+
+  // Context: Main Thread.  Signalled when work is complete.
+  sigslot::signal1<SignalThread *> SignalWorkDone;
+
+  enum { ST_MSG_WORKER_DONE, ST_MSG_FIRST_AVAILABLE };
+
+ protected:
+  ~SignalThread() override;
+
+  Thread* worker() { return &worker_; }
+
+  // Context: Main Thread.  Subclass should override to do pre-work setup.
+  virtual void OnWorkStart() { }
+
+  // Context: Worker Thread.  Subclass should override to do work.
+  virtual void DoWork() = 0;
+
+  // Context: Worker Thread.  Subclass should call periodically to
+  // dispatch messages and determine if the thread should terminate.
+  bool ContinueWork();
+
+  // Context: Worker Thread.  Subclass should override when extra work is
+  // needed to abort the worker thread.
+  virtual void OnWorkStop() { }
+
+  // Context: Main Thread.  Subclass should override to do post-work cleanup.
+  virtual void OnWorkDone() { }
+
+  // Context: Any Thread.  If subclass overrides, be sure to call the base
+  // implementation.  Do not use (message_id < ST_MSG_FIRST_AVAILABLE)
+  void OnMessage(Message* msg) override;
+
+ private:
+  enum State {
+    kInit,            // Initialized, but not started
+    kRunning,         // Started and doing work
+    kReleasing,       // Same as running, but to be deleted when work is done
+    kComplete,        // Work is done
+    kStopping,        // Work is being interrupted
+  };
+
+  class Worker : public Thread {
+   public:
+    explicit Worker(SignalThread* parent, bool use_socket_server)
+        : Thread(use_socket_server
+                     ? SocketServer::CreateDefault()
+                     : std::unique_ptr<SocketServer>(new NullSocketServer())),
+          parent_(parent) {}
+    ~Worker() override;
+    void Run() override;
+    bool IsProcessingMessages() override;
+
+   private:
+    SignalThread* parent_;
+
+    RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(Worker);
+  };
+
+  class SCOPED_LOCKABLE EnterExit {
+   public:
+    explicit EnterExit(SignalThread* t) EXCLUSIVE_LOCK_FUNCTION(t->cs_)
+        : t_(t) {
+      t_->cs_.Enter();
+      // If refcount_ is zero then the object has already been deleted and we
+      // will be double-deleting it in ~EnterExit()! (shouldn't happen)
+      RTC_DCHECK_NE(0, t_->refcount_);
+      ++t_->refcount_;
+    }
+    ~EnterExit() UNLOCK_FUNCTION() {
+      bool d = (0 == --t_->refcount_);
+      t_->cs_.Leave();
+      if (d)
+        delete t_;
+    }
+
+   private:
+    SignalThread* t_;
+
+    RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(EnterExit);
+  };
+
+  void Run();
+  void OnMainThreadDestroyed();
+
+  Thread* main_;
+  Worker worker_;
+  CriticalSection cs_;
+  State state_;
+  int refcount_;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(SignalThread);
+};
+
+///////////////////////////////////////////////////////////////////////////////
+
+}  // namespace rtc
+
+#endif  // WEBRTC_RTC_BASE_SIGNALTHREAD_H_