Fixes memory leak in shutting down gRPC streams.

Resolve #86.

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

.github/workflows/build-test.yml

@@ -160,6 +160,7 @@ jobs:
           ./build/bin/EtcdSyncTest
           ./build/bin/EtcdTest
           ./build/bin/LockTest
+          ./build/bin/MemLeakTest
           ./build/bin/WatcherTest
           ./build/bin/ElectionTest
 

src/Client.cpp

@@ -251,8 +251,6 @@ etcd::Client::Client(std::string const & address,
   grpc_args.SetLoadBalancingPolicyName(load_balancer);
   this->channel = grpc::CreateCustomChannel(addresses, creds, grpc_args);
 
-  std::cout << "this->channel : " << this->channel;
-
   // setup stubs
   stubs.reset(new EtcdServerStubs{});
   stubs->kvServiceStub = KV::NewStub(this->channel);

src/v3/AsyncElectionAction.cpp

@@ -190,9 +190,17 @@ void etcdv3::AsyncObserveAction::CancelObserve()
 {
   std::lock_guard<std::mutex> scope_lock(this->protect_is_cancalled);
   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) {
+      // ok
+    } else {
+      std::cerr << "Failed to finish a election observing connection" << std::endl;
+    }
+
     cq_.Shutdown();
   }
-  response_reader->Finish(&status, (void *)this);
 }
 
 bool etcdv3::AsyncObserveAction::Cancelled() const {

src/v3/AsyncLeaseAction.cpp

@@ -130,9 +130,25 @@ void etcdv3::AsyncLeaseKeepAliveAction::CancelKeepAlive()
   if(isCancelled == false)
   {
     isCancelled = true;
+
+    void *got_tag = nullptr;
+    bool ok = false;
+
     stream->WritesDone((void*)etcdv3::KEEPALIVE_DONE);
+    if (cq_.Next(&got_tag, &ok) && ok && got_tag == (void *)etcdv3::KEEPALIVE_DONE) {
+      // ok
+    } else {
+      std::cerr << "Failed to mark a lease keep-alive connection as DONE" << std::endl;
+    }
+
     grpc::Status status;
     stream->Finish(&status, (void *)this);
+    if (cq_.Next(&got_tag, &ok) && ok && got_tag == (void *)this) {
+      // ok
+    } else {
+      std::cerr << "Failed to finish a lease keep-alive connection" << std::endl;
+    }
+
     cq_.Shutdown();
   }
 }

src/v3/AsyncWatchAction.cpp

@@ -61,6 +61,9 @@ void etcdv3::AsyncWatchAction::waitForResponse()
     {
       break;
     }
+    if(isCancelled.load()) {
+      break;
+    }
     if(got_tag == (void*)etcdv3::WATCH_WRITES_DONE) {
       isCancelled.store(true);
       cq_.Shutdown();
@@ -79,9 +82,22 @@ void etcdv3::AsyncWatchAction::waitForResponse()
         // 1. watch for a future revision, return immediately with empty events set
         // 2. receive any effective events.
         isCancelled.store(true);
+
         stream->WritesDone((void*)etcdv3::WATCH_WRITES_DONE);
+        if (cq_.Next(&got_tag, &ok) && ok && got_tag == (void *)etcdv3::WATCH_WRITES_DONE) {
+          // ok
+        } else {
+          std::cerr << "WARN: Failed to mark a watch connection as DONE" << std::endl;
+        }
+
         grpc::Status status;
         stream->Finish(&status, (void *)this);
+        if (cq_.Next(&got_tag, &ok) && ok && got_tag == (void *)this) {
+          // ok
+        } else {
+          std::cerr << "WARN: Failed to finish a watch connection" << std::endl;
+        }
+
         cq_.Shutdown();
 
         // leave a warning if the response is too large and been fragmented
@@ -102,9 +118,24 @@ void etcdv3::AsyncWatchAction::CancelWatch()
 {
   std::lock_guard<std::mutex> scope_lock(this->protect_is_cancalled);
   if (!isCancelled.exchange(true)) {
+    void* got_tag;
+    bool ok = false;
+
     stream->WritesDone((void*)etcdv3::WATCH_WRITES_DONE);
+    if (cq_.Next(&got_tag, &ok) && ok && got_tag == (void *)etcdv3::WATCH_WRITES_DONE) {
+      // ok
+    } else {
+      std::cerr << "WARN: Failed to mark a watch connection as DONE" << std::endl;
+    }
+
     grpc::Status status;
     stream->Finish(&status, (void *)this);
+    if (cq_.Next(&got_tag, &ok) && ok && got_tag == (void *)this) {
+      // ok
+    } else {
+      std::cerr << "WARN: Failed to finish a watch connection" << std::endl;
+    }
+
     cq_.Shutdown();
   }
 }
@@ -124,6 +155,9 @@ void etcdv3::AsyncWatchAction::waitForResponse(std::function<void(etcd::Response
     {
       break;
     }
+    if(isCancelled.load()) {
+      break;
+    }
     if(got_tag == (void*)etcdv3::WATCH_WRITES_DONE)
     {
       isCancelled.store(true);

tst/MemLeakTest.cpp

@@ -0,0 +1,91 @@
+// See also: https://github.com/etcd-cpp-apiv3/etcd-cpp-apiv3/issues/86
+
+#include <future>
+#include <memory>
+
+#include "etcd/Client.hpp"
+#include "etcd/KeepAlive.hpp"
+
+class DistributedLock {
+public:
+    DistributedLock(const std::string &lock_name,
+                    uint timeout = 0);
+    ~DistributedLock() noexcept;
+    inline bool lock_acquired() {
+      return _acquired;
+    }
+
+private:
+    bool _acquired = false;
+    std::string _lock_key;
+    std::unique_ptr<::etcd::Client> _etcd_client;
+};
+
+DistributedLock::DistributedLock(const std::string &lock_name,
+                                 uint timeout) {
+  _etcd_client = std::unique_ptr<etcd::Client>(new etcd::Client("localhost:2379"));
+
+  try {
+    if (timeout == 0) {
+      etcd::Response resp = _etcd_client->lock(lock_name).get();
+      if (resp.is_ok()) {
+        _lock_key = resp.lock_key();
+        _acquired = true;
+      }
+    } else {
+      std::future<etcd::Response> future = std::async(std::launch::async, [&]() {
+          etcd::Response resp = _etcd_client->lock(lock_name).get();
+          return resp;
+      });
+
+      std::future_status status = future.wait_for(std::chrono::seconds(timeout));
+      if (status == std::future_status::ready) {
+        auto resp = future.get();
+        if (resp.is_ok()) {
+          _lock_key = resp.lock_key();
+          _acquired = true;
+        }
+      } else if (status == std::future_status::timeout) {
+        std::cerr << "failed to acquire distributed because of lock timeout" << std::endl;
+      } else {
+        std::cerr << "failed to acquire distributed lock" << std::endl;
+      }
+    }
+  } catch (std::exception &e) {
+    throw e;
+  }
+}
+
+DistributedLock::~DistributedLock() noexcept {
+  if (!_acquired) {
+    return;
+  }
+
+  try {
+    auto resp = _etcd_client->unlock(_lock_key).get();
+    if (!resp.is_ok()) {
+      std::cout << resp.error_code() << std::endl;
+    }
+  } catch (std::exception &e) {
+    throw e;
+  }
+}
+
+int main() {
+  int i = 0, t = 0;
+  while(t < 500) {
+    {
+      DistributedLock lock(std::to_string(i), 0);
+      if(!lock.lock_acquired()) {
+        std::cerr << "failed to acquire lock" << std::endl;
+      }
+      std::this_thread::sleep_for(std::chrono::milliseconds(1));
+    }
+    ++i;
+    ++t;
+    if (i == 10) {
+      i = 0;
+    }
+    std::cout << "round: i = " << i << ", t = " << t << std::endl;
+  }
+}