Fix deadlock closing socket on another thread

src/socket.cpp

@@ -169,20 +169,20 @@ class dap::Socket::Shared : public dap::ReaderWriter {
   }
 
   void close() {
-#if !defined(_WIN32)
     {
       RLock l(mutex);
       if (s != InvalidSocket) {
+#if defined(_WIN32)
+        closesocket(s);
+#else
         ::shutdown(s, SHUT_RDWR);
+#endif
       }
     }
-#endif
 
     WLock l(mutex);
     if (s != InvalidSocket) {
-#if defined(_WIN32)
-      closesocket(s);
-#else
+#if !defined(_WIN32)
       ::close(s);
 #endif
       s = InvalidSocket;

src/socket_test.cpp

@@ -18,8 +18,61 @@
 #include "gtest/gtest.h"
 
 #include <chrono>
+#include <thread>
 #include <vector>
 
+// Basic socket send & receive test
+TEST(Socket, SendRecv) {
+  const char* port = "19021";
+
+  auto server = dap::Socket("localhost", port);
+
+  auto client = dap::Socket::connect("localhost", port, 0);
+  ASSERT_TRUE(client != nullptr);
+
+  const std::string expect = "Hello World!";
+  std::string read;
+
+  auto thread = std::thread([&] {
+    auto conn = server.accept();
+    ASSERT_TRUE(conn != nullptr);
+    char c;
+    while (conn->read(&c, 1) != 0) {
+      read += c;
+    }
+  });
+
+  ASSERT_TRUE(client->write(expect.data(), expect.size()));
+
+  client->close();
+  thread.join();
+
+  ASSERT_EQ(read, expect);
+}
+
+// See https://github.com/google/cppdap/issues/37
+TEST(Socket, CloseOnDifferentThread) {
+  const char* port = "19021";
+
+  auto server = dap::Socket("localhost", port);
+
+  auto client = dap::Socket::connect("localhost", port, 0);
+  ASSERT_TRUE(client != nullptr);
+
+  auto conn = server.accept();
+
+  auto thread = std::thread([&] {
+    // Closing client on different thread should unblock client->read().
+    client->close();
+  });
+
+  char c;
+  while (client->read(&c, 1) != 0) {
+  }
+
+  thread.join();
+}
+
 TEST(Socket, ConnectTimeout) {
   const char* port = "19021";
   const int timeoutMillis = 200;