Fixes race condition (repeatly cancel) in watch.

Signed-off-by: Tao He <sighingnow@gmail.com>

etcd/Watcher.hpp

@@ -1,6 +1,7 @@
 #ifndef __ETCD_WATCHER_HPP__
 #define __ETCD_WATCHER_HPP__
 
+#include <atomic>
 #include <functional>
 #include <string>
 #include <thread>
@@ -98,6 +99,7 @@ namespace etcd
   private:
     int fromIndex;
     bool recursive;
+    std::atomic_bool cancelled;
   };
 }
 

etcd/v3/AsyncWatchAction.hpp

@@ -1,6 +1,7 @@
 #ifndef __ASYNC_WATCHACTION_HPP__
 #define __ASYNC_WATCHACTION_HPP__
 
+#include <atomic>
 #include <mutex>
 
 #include <grpc++/grpc++.h>
@@ -28,7 +29,7 @@ namespace etcdv3
     private:
       WatchResponse reply;
       std::unique_ptr<ClientAsyncReaderWriter<WatchRequest,WatchResponse>> stream;   
-      bool isCancelled;
+      std::atomic_bool isCancelled;
       std::mutex protect_is_cancalled;
   };
 }

src/KeepAlive.cpp

@@ -115,7 +115,9 @@ void etcd::KeepAlive::Cancel()
 
   // clean up
   context.stop();
-  task_.join();
+  if (task_.joinable()) {
+    task_.join();
+  }
 }
 
 void etcd::KeepAlive::Check() {

src/Watcher.cpp

@@ -92,16 +92,15 @@ etcd::Watcher::Watcher(std::string const & address,
 
 etcd::Watcher::~Watcher()
 {
-  stubs->call->CancelWatch();
-  if (task_.joinable()) {
-    task_.join();
-  }
+  this->Cancel();
 }
 
 bool etcd::Watcher::Wait()
 {
-  if (task_.joinable()) {
-    task_.join();
+  if (cancelled.exchange(true)) {
+    if (task_.joinable()) {
+      task_.join();
+    }
   }
   return stubs->call->Cancelled();
 }
@@ -144,4 +143,5 @@ void etcd::Watcher::doWatch(std::string const & key,
       wait_callback(stubs->call->Cancelled());
     }
   });
+  cancelled.store(false);
 }

src/v3/AsyncWatchAction.cpp

@@ -9,7 +9,7 @@ using etcdserverpb::WatchCreateRequest;
 etcdv3::AsyncWatchAction::AsyncWatchAction(etcdv3::ActionParameters param)
   : etcdv3::Action(param) 
 {
-  isCancelled = false;
+  isCancelled.store(false);
   stream = parameters.watch_stub->AsyncWatch(&context,&cq_,(void*)"create");
 
   WatchRequest watch_req;
@@ -61,14 +61,14 @@ void etcdv3::AsyncWatchAction::waitForResponse()
       break;
     }
     if(got_tag == (void*)"writes done") {
-      isCancelled = true;
+      isCancelled.store(true);
       cq_.Shutdown();
       break;
     }
     if(got_tag == (void*)this) // read tag
     {
       if (reply.canceled()) {
-        isCancelled = true;
+        isCancelled.store(true);
         cq_.Shutdown();
       }
       else if ((reply.created() && reply.header().revision() < parameters.revision) ||
@@ -77,7 +77,7 @@ void etcdv3::AsyncWatchAction::waitForResponse()
         //
         // 1. watch for a future revision, return immediately with empty events set
         // 2. receive any effective events.
-        isCancelled = true;
+        isCancelled.store(true);
         stream->WritesDone((void*)"writes done");
         grpc::Status status;
         stream->Finish(&status, (void *)this);
@@ -100,9 +100,7 @@ void etcdv3::AsyncWatchAction::waitForResponse()
 void etcdv3::AsyncWatchAction::CancelWatch()
 {
   std::lock_guard<std::mutex> scope_lock(this->protect_is_cancalled);
-  if(isCancelled == false)
-  {
-    isCancelled = true;
+  if (!isCancelled.exchange(true)) {
     stream->WritesDone((void*)"writes done");
     grpc::Status status;
     stream->Finish(&status, (void *)this);
@@ -111,7 +109,7 @@ void etcdv3::AsyncWatchAction::CancelWatch()
 }
 
 bool etcdv3::AsyncWatchAction::Cancelled() const {
-  return isCancelled;
+  return isCancelled.load();
 }
 
 void etcdv3::AsyncWatchAction::waitForResponse(std::function<void(etcd::Response)> callback) 
@@ -127,14 +125,14 @@ void etcdv3::AsyncWatchAction::waitForResponse(std::function<void(etcd::Response
     }
     if(got_tag == (void*)"writes done")
     {
-      isCancelled = true;
+      isCancelled.store(true);
       cq_.Shutdown();
       break;
     }
     else if(got_tag == (void*)this) // read tag
     {
       if (reply.canceled()) {
-        isCancelled = true;
+        isCancelled.store(true);
         cq_.Shutdown();
         if (reply.compact_revision() != 0) {
           callback(etcd::Response(grpc::StatusCode::OUT_OF_RANGE /* error code */,
@@ -159,7 +157,6 @@ void etcdv3::AsyncWatchAction::waitForResponse(std::function<void(etcd::Response
 
 etcdv3::AsyncWatchResponse etcdv3::AsyncWatchAction::ParseResponse()
 {
-
   AsyncWatchResponse watch_resp;
   if(!status.ok())
   {