Fixes the implementation of Observe() (#231)

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

README.md

@@ -877,7 +877,7 @@ pplx::task<Response> proclaim(std::string const &name, int64_t lease_id,
 
 pplx::task<Response> leader(std::string const &name);
 
-std::unique_ptr<Observer> observe(std::string const &name);
+std::unique_ptr<SyncClient::Observer> observe(std::string const &name);
 
 pplx::task<Response> resign(std::string const &name, int64_t lease_id,
                             std::string const &key, int64_t revision);
@@ -891,7 +891,7 @@ The `Observer` returned by `observe()` can be use to monitor the changes of elec
 The observer stream will be canceled when been destructed.
 
 ```c++
-  std::unique_ptr<etcd::Observer> observer = etcd.observe("test");
+  std::unique_ptr<etcd::SyncClient::Observer> observer = etcd.observe("test");
 
   // wait one change event, blocked execution
   etcd::Response resp = observer->WaitOnce();
@@ -906,7 +906,7 @@ The observer stream will be canceled when been destructed.
   observer.reset(nullptr);
 ```
 
-for more details, please refer to [etcd/Client.hpp](./etcd/Client.hpp).
+for more details, please refer to [etcd/Client.hpp](./etcd/Client.hpp) and [tst/ElectionTest.cpp](./tst/ElectionTest.cpp).
 
 ### TODO
 

etcd/v3/action_constants.hpp

@@ -45,6 +45,7 @@ namespace etcdv3
   extern char const * WATCH_FINISH;
 
   extern char const * ELECTION_OBSERVE_CREATE;
+  extern char const * ELECTION_OBSERVE_FINISH;
 
   extern const int ERROR_GRPC_OK;
   extern const int ERROR_GRPC_CANCELLED;

src/v3/AsyncGRPC.cpp

@@ -817,10 +817,7 @@ void etcdv3::AsyncObserveAction::waitForResponse()
   response_reader->Read(&reply, (void *)this);
   if (cq_.Next(&got_tag, &ok) && ok && got_tag == (void*)this) {
     auto response = ParseResponse();
-    if (response.get_error_code() == 0) {
+    if (response.get_error_code() != 0) {
-      // issue the next read
-      response_reader->Read(&reply, (void *)this);
-    } else {
       this->CancelObserve();
     }
   } else {
@@ -835,12 +832,24 @@ void etcdv3::AsyncObserveAction::CancelObserve()
   if (!isCancelled.exchange(true)) {
     void* got_tag;
     bool ok = false;
-    response_reader->Finish(&status, (void *)this);
+
-    if (cq_.Next(&got_tag, &ok) && ok && got_tag == (void *)this) {
+    response_reader->Finish(&status, (void *)ELECTION_OBSERVE_FINISH);
-      // ok
+
-    } else {
+    // FIXME: not sure why the `Next()` after `Finish()` blocks forever.
+    // Using the `AsyncNext()` without a timeout to ensure the cancel is done.
+    switch (cq_.AsyncNext(&got_tag, &ok, std::chrono::system_clock::now() + std::chrono::microseconds(1))) {
+      case CompletionQueue::NextStatus::TIMEOUT:
+      case CompletionQueue::NextStatus::SHUTDOWN:
+        // ignore
+        break;
+      case CompletionQueue::NextStatus::GOT_EVENT:
+        if (!ok || got_tag != (void *)ELECTION_OBSERVE_FINISH) {
           std::cerr << "Failed to finish a election observing connection" << std::endl;
         }
+    }
+
+    // cancel on-the-fly calls
+    context.TryCancel();
 
     cq_.Shutdown();
   }

src/v3/action_constants.cpp

@@ -42,6 +42,7 @@ char const * etcdv3::WATCH_WRITES_DONE = "watch writes done";
 char const * etcdv3::WATCH_FINISH = "watch finish";
 
 char const * etcdv3::ELECTION_OBSERVE_CREATE = "observe create";
+char const * etcdv3::ELECTION_OBSERVE_FINISH = "observe finish";
 
 const int etcdv3::ERROR_GRPC_OK = 0;
 const int etcdv3::ERROR_GRPC_CANCELLED = 1;

tst/ElectionTest.cpp

@@ -55,6 +55,60 @@ TEST_CASE("campaign and resign")
   REQUIRE(0 == resp5.error_code());
 }
 
+TEST_CASE("campaign and observe")
+{
+  etcd::Client etcd(etcd_url);
+
+  auto keepalive = etcd.leasekeepalive(60).get();
+  auto lease_id = keepalive->Lease();
+
+  auto observer_thread = std::thread([&etcd]() {
+    std::unique_ptr<etcd::SyncClient::Observer> observer = etcd.observe("test");
+    // wait many change events, blocked execution
+    for (size_t i = 0; i < 10; ++i) {
+      etcd::Response resp = observer->WaitOnce();
+      std::cout << "observe " << resp.value().key() << " as the leader: " << resp.value().as_string() << std::endl;
+    }
+    std::cout << "finish the observe" << std::endl;
+    // cancel the observers
+    observer.reset(nullptr);
+  });
+
+  std::this_thread::sleep_for(std::chrono::seconds(1));
+
+  for (int i = 0; i < 5; ++i) {
+    // campaign
+    auto resp1 = etcd.campaign("test", lease_id, "xxxx").get();
+    REQUIRE(0 == resp1.error_code());
+    std::cout << "key " << resp1.value().key() << " becomes the leader"
+              << std::endl;
+
+    // proclaim
+    auto resp3 = etcd.proclaim("test", lease_id, resp1.value().key(),
+                               resp1.value().created_index(),
+                               "tttt - " + std::to_string(i))
+                     .get();
+    REQUIRE(0 == resp3.error_code());
+
+    // leader
+    {
+      auto resp4 = etcd.leader("test").get();
+      REQUIRE(0 == resp4.error_code());
+      REQUIRE(resp1.value().key() == resp4.value().key());
+      REQUIRE("tttt - " + std::to_string(i) == resp4.value().as_string());
+    }
+
+    // resign
+    auto resp5 = etcd.resign("test", lease_id, resp1.value().key(),
+                             resp1.value().created_index())
+                     .get();
+    REQUIRE(0 == resp5.error_code());
+    std::this_thread::sleep_for(std::chrono::seconds(1));
+  }
+
+  observer_thread.join();
+}
+
 TEST_CASE("cleanup")
 {
   etcd::Client etcd(etcd_url);