Delete SignalThread class.

webrtc/rtc_base/nethelpers.cc

Index: webrtc/rtc_base/nethelpers.cc
diff --git a/webrtc/rtc_base/nethelpers.cc b/webrtc/rtc_base/nethelpers.cc
index 6c11ef8c38fa04800df834bc8fa0f0f8939b3b89..6a411a6fc55b7cf22534cc8a3fe182fc8f98f7bf 100644
--- a/webrtc/rtc_base/nethelpers.cc
+++ b/webrtc/rtc_base/nethelpers.cc
@@ -25,13 +25,17 @@
 #endif
 #endif  // defined(WEBRTC_POSIX) && !defined(__native_client__)
 
+#include "webrtc/base/bind.h"
 #include "webrtc/base/byteorder.h"
 #include "webrtc/base/checks.h"
 #include "webrtc/base/logging.h"
-#include "webrtc/base/signalthread.h"
+#include "webrtc/base/ptr_util.h"
+#include "webrtc/base/task_queue.h"
+#include "webrtc/base/thread.h"
 
 namespace rtc {
 
+namespace {
 int ResolveHostname(const std::string& hostname, int family,
                     std::vector<IPAddress>* addresses) {
 #ifdef __native_client__
@@ -81,17 +85,54 @@ int ResolveHostname(const std::string& hostname, int family,
   return 0;
 #endif  // !__native_client__
 }
+}  // namespace
 
 // AsyncResolver
-AsyncResolver::AsyncResolver()
-    : SignalThread(false /* use_socket_server */), error_(-1) {}
+AsyncResolver::AsyncResolver() : construction_thread_(Thread::Current()) {
+  RTC_DCHECK(construction_thread_);
+}
+
+AsyncResolver::~AsyncResolver() {
+  RTC_DCHECK(construction_thread_->IsCurrent());
+  if (state_)
+    // It's possible that we have a posted message waiting on the MessageQueue
+    // refering to this object. Indirection via the ref-counted state_ object
+    // ensure it doesn't access us after deletion.
 
-AsyncResolver::~AsyncResolver() = default;
+    // TODO(nisse): An alternative approach to solve this problem would be to
+    // extend MessageQueue::Clear in some way to let us selectively cancel posts
+    // directed to this object. Then we wouldn't need any ref count, but its a
+    // larger change to the MessageQueue.
+    state_->resolver = nullptr;
+}
 
 void AsyncResolver::Start(const SocketAddress& addr) {
+  RTC_DCHECK_RUN_ON(construction_thread_);
+  RTC_DCHECK(!resolver_queue_);
+  RTC_DCHECK(!state_);
+  // TODO(nisse): Support injection of task queue at construction?
+  resolver_queue_ = rtc::MakeUnique<TaskQueue>("AsyncResolverQueue");
   addr_ = addr;
-  // SignalThred Start will kickoff the resolve process.
-  SignalThread::Start();
+  state_ = new RefCountedObject<Trampoline>(this);
+
+  // These member variables need to be copied to local variables to make it
+  // possible to capture them, even for capture-by-copy.
+  scoped_refptr<Trampoline> state = state_;
+  rtc::Thread* construction_thread = construction_thread_;
+  resolver_queue_->PostTask([state, addr, construction_thread]() {
+    std::vector<IPAddress> addresses;
+    int error =
+        ResolveHostname(addr.hostname().c_str(), addr.family(), &addresses);
+    // Ensure SignalDone is called on the main thread.
+    // TODO(nisse): Should use move of the address list, but not easy until
+    // C++17. Since this code isn't performance critical, copy should be fine
+    // for now.
+    construction_thread->Post(RTC_FROM_HERE, [state, error, addresses]() {
+      if (!state->resolver)
+        return;
+      state->resolver->ResolveDone(error, std::move(addresses));
+    });
+  });
 }
 
 bool AsyncResolver::GetResolvedAddress(int family, SocketAddress* addr) const {
@@ -113,16 +154,41 @@ int AsyncResolver::GetError() const {
 }
 
 void AsyncResolver::Destroy(bool wait) {
-  SignalThread::Destroy(wait);
+  RTC_DCHECK_RUN_ON(construction_thread_);
+  RTC_DCHECK(!state_ || state_->resolver);
+  // If we don't wait here, we will nevertheless wait in the destructor.
+  if (wait || !state_) {
+    // Destroy task queue, blocks on any currently running task. If we have a
+    // pending task, it will post a call to attempt to call ResolveDone before
+    // finishing, which we will never handle.
+    delete this;
+  } else {
+    destroyed_ = true;
+  }
 }
 
-void AsyncResolver::DoWork() {
-  error_ = ResolveHostname(addr_.hostname().c_str(), addr_.family(),
-                           &addresses_);
-}
+void AsyncResolver::ResolveDone(int error, std::vector<IPAddress> addresses) {
+  RTC_DCHECK_RUN_ON(construction_thread_);
+  error_ = error;
+  addresses_ = std::move(addresses);
+  if (destroyed_) {
+    delete this;
+    return;
+  } else {
+    // Beware that SignalDone may call Destroy.
 
-void AsyncResolver::OnWorkDone() {
-  SignalDone(this);
+    // TODO(nisse): Currently allows only Destroy(false) in this case,
+    // and that's what all webrtc code is using. With Destroy(true),
+    // this object would be destructed immediately, and the access
+    // both to |destroyed_| below as well as the sigslot machinery
+    // involved in SignalDone implies invalid use-after-free.
+    SignalDone(this);
+    if (destroyed_) {
+      delete this;
+      return;
+    }
+  }
+  state_ = nullptr;
 }
 
 const char* inet_ntop(int af, const void *src, char* dst, socklen_t size) {