unix: implement uv_stream_set_blocking()

Commit 393c1c5 ("unix: set non-block mode in uv_{pipe,tcp,udp}_open")
causes a regression in the io.js cluster module.

The io.js documentation states that `worker.send()` and `process.send()`
are synchronous but they no longer were after upgrading to libuv v1.2.1.

The reason they are synchronous is because of backpressure - or rather,
lack of backpressure: a slow consumer eventually causes a fast producer
to run out of memory because the backlog of pending messages in the
producer can grow unchecked.

Ergo, implement uv_stream_set_blocking() on UNIX platforms to let io.js
enable the old blocking behavior for pipes again.

Refs: nodejs/node#760

Makefile.am

@@ -189,6 +189,7 @@ test_run_tests_SOURCES = test/blackhole-server.c \
                          test/test-pipe-sendmsg.c \
                          test/test-pipe-server-close.c \
                          test/test-pipe-close-stdout-read-stdin.c \
+                         test/test-pipe-set-non-blocking.c \
                          test/test-platform-output.c \
                          test/test-poll-close.c \
                          test/test-poll-close-doesnt-corrupt-stack.c \

docs/src/stream.rst

@@ -206,8 +206,8 @@ API
         Relying too much on this API is not recommended. It is likely to change
         significantly in the future.
 
-        Currently this only works on Windows and only for
-        :c:type:`uv_pipe_t` handles.
+        Currently only works on Windows for :c:type:`uv_pipe_t` handles.
+        On UNIX platforms, all :c:type:`uv_stream_t` handles are supported.
 
         Also libuv currently makes no ordering guarantee when the blocking mode
         is changed after write requests have already been submitted. Therefore it is

src/unix/stream.c

@@ -1573,5 +1573,8 @@ void uv__stream_close(uv_stream_t* handle) {
 
 
 int uv_stream_set_blocking(uv_stream_t* handle, int blocking) {
-  return UV_ENOSYS;
+  /* Don't need to check the file descriptor, uv__nonblock()
+   * will fail with EBADF if it's not valid.
+   */
+  return uv__nonblock(uv__stream_fd(handle), !blocking);
 }

test/test-list.h

@@ -167,6 +167,7 @@ TEST_DECLARE   (pipe_ref4)
 #ifndef _WIN32
 TEST_DECLARE   (pipe_close_stdout_read_stdin)
 #endif
+TEST_DECLARE   (pipe_set_non_blocking)
 TEST_DECLARE   (process_ref)
 TEST_DECLARE   (has_ref)
 TEST_DECLARE   (active)
@@ -339,6 +340,7 @@ TASK_LIST_START
 #ifndef _WIN32
   TEST_ENTRY  (pipe_close_stdout_read_stdin)
 #endif
+  TEST_ENTRY  (pipe_set_non_blocking)
   TEST_ENTRY  (tty)
   TEST_ENTRY  (stdio_over_pipes)
   TEST_ENTRY  (ip6_pton)

test/test-pipe-set-non-blocking.c

@@ -0,0 +1,99 @@
+/* Copyright (c) 2015, Ben Noordhuis <info@bnoordhuis.nl>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "uv.h"
+#include "task.h"
+
+#ifdef _WIN32
+
+TEST_IMPL(pipe_set_non_blocking) {
+  RETURN_SKIP("Test not implemented on Windows.");
+}
+
+#else  /* !_WIN32 */
+
+#include <errno.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+struct thread_ctx {
+  uv_barrier_t barrier;
+  int fd;
+};
+
+static void thread_main(void* arg) {
+  struct thread_ctx* ctx;
+  char buf[4096];
+  ssize_t n;
+
+  ctx = arg;
+  uv_barrier_wait(&ctx->barrier);
+
+  do
+    n = read(ctx->fd, buf, sizeof(buf));
+  while (n > 0 || (n == -1 && errno == EINTR));
+
+  ASSERT(n == 0);
+}
+
+TEST_IMPL(pipe_set_non_blocking) {
+  struct thread_ctx ctx;
+  uv_pipe_t pipe_handle;
+  uv_thread_t thread;
+  size_t nwritten;
+  char data[4096];
+  uv_buf_t buf;
+  int fd[2];
+  int n;
+
+  ASSERT(0 == uv_pipe_init(uv_default_loop(), &pipe_handle, 0));
+  ASSERT(0 == socketpair(AF_UNIX, SOCK_STREAM, 0, fd));
+  ASSERT(0 == uv_pipe_open(&pipe_handle, fd[0]));
+  ASSERT(0 == uv_stream_set_blocking((uv_stream_t*) &pipe_handle, 1));
+
+  ctx.fd = fd[1];
+  ASSERT(0 == uv_barrier_init(&ctx.barrier, 2));
+  ASSERT(0 == uv_thread_create(&thread, thread_main, &ctx));
+  uv_barrier_wait(&ctx.barrier);
+
+  buf.len = sizeof(data);
+  buf.base = data;
+  memset(data, '.', sizeof(data));
+
+  nwritten = 0;
+  while (nwritten < 10 << 20) {
+    /* The stream is in blocking mode so uv_try_write() should always succeed
+     * with the exact number of bytes that we wanted written.
+     */
+    n = uv_try_write((uv_stream_t*) &pipe_handle, &buf, 1);
+    ASSERT(n == sizeof(data));
+    nwritten += n;
+  }
+
+  uv_close((uv_handle_t*) &pipe_handle, NULL);
+  ASSERT(0 == uv_run(uv_default_loop(), UV_RUN_DEFAULT));
+
+  ASSERT(0 == close(fd[1]));  /* fd[0] is closed by uv_close(). */
+  ASSERT(0 == uv_thread_join(&thread));
+  uv_barrier_destroy(&ctx.barrier);
+
+  MAKE_VALGRIND_HAPPY();
+  return 0;
+}
+
+#endif  /* !_WIN32 */

uv.gyp

@@ -329,6 +329,7 @@
         'test/test-pipe-sendmsg.c',
         'test/test-pipe-server-close.c',
         'test/test-pipe-close-stdout-read-stdin.c',
+        'test/test-pipe-set-non-blocking.c',
         'test/test-platform-output.c',
         'test/test-poll.c',
         'test/test-poll-close.c',