Merge (manually) the subprocess_stream into default

* Add a new asyncio.subprocess module
* Add new create_subprocess_exec() and create_subprocess_shell() functions
* The new asyncio.subprocess.SubprocessStreamProtocol creates stream readers
  for stdout and stderr and a stream writer for stdin.
* The new asyncio.subprocess.Process class offers an API close to the
  subprocess.Popen class:

  - pid, returncode, stdin, stdout and stderr attributes
  - communicate(), wait(), send_signal(), terminate() and kill() methods

* Remove STDIN (0), STDOUT (1) and STDERR (2) constants from base_subprocess
  and unix_events, to not be confused with the symbols with the same name of
  subprocess and asyncio.subprocess modules
* _ProactorBasePipeTransport.get_write_buffer_size() now counts also the size
  of the pending write
* _ProactorBaseWritePipeTransport._loop_writing() may now pause the protocol if
  the write buffer size is greater than the high water mark (64 KB by default)
* Add new subprocess examples: shell.py, subprocess_shell.py,
* subprocess_attach_read_pipe.py and subprocess_attach_write_pipe.py

1 files changed, 33 insertions, 0 deletions

diff --git a/examples/subprocess_attach_write_pipe.py b/examples/subprocess_attach_write_pipe.py
new file mode 100644
index 0000000..017b827
--- /dev/null
+++ b/examples/subprocess_attach_write_pipe.py
@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+"""Example showing how to attach a write pipe to a subprocess."""
+import asyncio
+import os, sys
+from asyncio import subprocess
+
+code = """
+import os, sys
+fd = int(sys.argv[1])
+data = os.read(fd, 1024)
+sys.stdout.buffer.write(data)
+"""
+
+loop = asyncio.get_event_loop()
+
+@asyncio.coroutine
+def task():
+    rfd, wfd = os.pipe()
+    args = [sys.executable, '-c', code, str(rfd)]
+    proc = yield from asyncio.create_subprocess_exec(
+                          *args,
+                          pass_fds={rfd},
+                          stdout=subprocess.PIPE)
+
+    pipe = open(wfd, 'wb', 0)
+    transport, _ = yield from loop.connect_write_pipe(asyncio.Protocol,
+                                                      pipe)
+    transport.write(b'data')
+
+    stdout, stderr = yield from proc.communicate()
+    print("stdout = %r" % stdout.decode())
+
+loop.run_until_complete(task())