8319055: JCMD should not buffer the whole output of commands

Reviewed-by: stuefe, jsjolen

Author: Alex Menkov

src/hotspot/os/posix/attachListener_posix.cpp

@@ -114,6 +114,7 @@ class SocketChannel : public AttachOperation::RequestReader, public AttachOperat
 
   void close() {
     if (opened()) {
+      ::shutdown(_socket, SHUT_RDWR);
       ::close(_socket);
       _socket = -1;
     }
@@ -132,9 +133,8 @@ class SocketChannel : public AttachOperation::RequestReader, public AttachOperat
     RESTARTABLE(::write(_socket, buffer, size), n);
     return checked_cast<int>(n);
   }
-  // called after writing all data
+
   void flush() override {
-    ::shutdown(_socket, SHUT_RDWR);
   }
 };
 
@@ -144,13 +144,16 @@ class PosixAttachOperation: public AttachOperation {
   SocketChannel _socket_channel;
 
  public:
+  PosixAttachOperation(int socket) : AttachOperation(), _socket_channel(socket) {}
+
   void complete(jint res, bufferedStream* st) override;
 
-  PosixAttachOperation(int socket) : AttachOperation(), _socket_channel(socket) {
+  ReplyWriter* get_reply_writer() override {
+    return &_socket_channel;
   }
 
   bool read_request() {
-    return AttachOperation::read_request(&_socket_channel, &_socket_channel);
+    return _socket_channel.read_request(this, &_socket_channel);
   }
 };
 
@@ -318,11 +321,6 @@ PosixAttachOperation* PosixAttachListener::dequeue() {
 // socket could be made non-blocking and a timeout could be used.
 
 void PosixAttachOperation::complete(jint result, bufferedStream* st) {
-  JavaThread* thread = JavaThread::current();
-  ThreadBlockInVM tbivm(thread);
-
-  write_reply(&_socket_channel, result, st);
-
   delete this;
 }
 

src/hotspot/os/windows/attachListener_windows.cpp

@@ -92,6 +92,7 @@ class PipeChannel : public AttachOperation::RequestReader, public AttachOperatio
 
   void close() {
     if (opened()) {
+      FlushFileBuffers(_hPipe);
       CloseHandle(_hPipe);
       _hPipe = INVALID_HANDLE_VALUE;
     }
@@ -123,15 +124,13 @@ class PipeChannel : public AttachOperation::RequestReader, public AttachOperatio
                               &written,
                               nullptr);  // not overlapped
     if (!fSuccess) {
-        log_error(attach)("pipe write error (%d)", GetLastError());
-        return -1;
+      log_error(attach)("pipe write error (%d)", GetLastError());
+      return -1;
     }
     return (int)written;
   }
 
   void flush() override {
-    assert(opened(), "must be");
-    FlushFileBuffers(_hPipe);
   }
 };
 
@@ -151,11 +150,15 @@ class Win32AttachOperation: public AttachOperation {
   }
 
   bool read_request() {
-    return AttachOperation::read_request(&_pipe, &_pipe);
+    return _pipe.read_request(this, &_pipe);
   }
 
 public:
   void complete(jint result, bufferedStream* result_stream) override;
+
+  ReplyWriter* get_reply_writer() override {
+    return &_pipe;
+  }
 };
 
 
@@ -432,11 +435,6 @@ Win32AttachOperation* Win32AttachListener::dequeue() {
 }
 
 void Win32AttachOperation::complete(jint result, bufferedStream* result_stream) {
-  JavaThread* thread = JavaThread::current();
-  ThreadBlockInVM tbivm(thread);
-
-  write_reply(&_pipe, result, result_stream);
-
   delete this;
 }