Issue #20400: Merge Tulip into Python: add the new asyncio.subprocess module

* 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)

1 files changed, 9 insertions, 14 deletions

diff --git a/Lib/asyncio/base_subprocess.py b/Lib/asyncio/base_subprocess.py
index b7cdbce..b78f816 100644
--- a/Lib/asyncio/base_subprocess.py
+++ b/Lib/asyncio/base_subprocess.py
@@ -6,11 +6,6 @@ from . import tasks
 from . import transports
 
 
-STDIN = 0
-STDOUT = 1
-STDERR = 2
-
-
 class BaseSubprocessTransport(transports.SubprocessTransport):
 
     def __init__(self, loop, protocol, args, shell,
@@ -22,11 +17,11 @@ class BaseSubprocessTransport(transports.SubprocessTransport):
 
         self._pipes = {}
         if stdin == subprocess.PIPE:
-            self._pipes[STDIN] = None
+            self._pipes[0] = None
         if stdout == subprocess.PIPE:
-            self._pipes[STDOUT] = None
+            self._pipes[1] = None
         if stderr == subprocess.PIPE:
-            self._pipes[STDERR] = None
+            self._pipes[2] = None
         self._pending_calls = collections.deque()
         self._finished = False
         self._returncode = None
@@ -76,19 +71,19 @@ class BaseSubprocessTransport(transports.SubprocessTransport):
         loop = self._loop
         if proc.stdin is not None:
             _, pipe = yield from loop.connect_write_pipe(
-                lambda: WriteSubprocessPipeProto(self, STDIN),
+                lambda: WriteSubprocessPipeProto(self, 0),
                 proc.stdin)
-            self._pipes[STDIN] = pipe
+            self._pipes[0] = pipe
         if proc.stdout is not None:
             _, pipe = yield from loop.connect_read_pipe(
-                lambda: ReadSubprocessPipeProto(self, STDOUT),
+                lambda: ReadSubprocessPipeProto(self, 1),
                 proc.stdout)
-            self._pipes[STDOUT] = pipe
+            self._pipes[1] = pipe
         if proc.stderr is not None:
             _, pipe = yield from loop.connect_read_pipe(
-                lambda: ReadSubprocessPipeProto(self, STDERR),
+                lambda: ReadSubprocessPipeProto(self, 2),
                 proc.stderr)
-            self._pipes[STDERR] = pipe
+            self._pipes[2] = pipe
 
         assert self._pending_calls is not None