Commit 2aad64bb authored by Kirill Smelkov's avatar Kirill Smelkov

golang: Add support for nil channel

Send/recv on the nil channel block forever; close panics.
If a nil channel is used in select - corresponding case is never selected.

Setting channel to nil is a usual idiom in Go to disable processing some
cases in select. Nil channel is also used as "done" for e.g.
context.Background() - for contexts that can be never canceled.
parent 262f8986
...@@ -51,8 +51,9 @@ Goroutines and channels ...@@ -51,8 +51,9 @@ Goroutines and channels
`go` spawns a coroutine, or thread if gevent was not activated. It is possible to `go` spawns a coroutine, or thread if gevent was not activated. It is possible to
exchange data in between either threads or coroutines via channels. `chan` exchange data in between either threads or coroutines via channels. `chan`
creates a new channel with Go semantic - either synchronous or buffered. Use creates a new channel with Go semantic - either synchronous or buffered. Use
`chan.recv`, `chan.send` and `chan.close` for communication. `select` can be `chan.recv`, `chan.send` and `chan.close` for communication. `nilchan`
used to multiplex on several channels. For example:: stands for the nil channel. `select` can be used to multiplex on several
channels. For example::
ch1 = chan() # synchronous channel ch1 = chan() # synchronous channel
ch2 = chan(3) # channel with buffer of size 3 ch2 = chan(3) # channel with buffer of size 3
...@@ -65,22 +66,28 @@ used to multiplex on several channels. For example:: ...@@ -65,22 +66,28 @@ used to multiplex on several channels. For example::
ch1.recv() # will give 'a' ch1.recv() # will give 'a'
ch2.recv_() # will give ('b', True) ch2.recv_() # will give ('b', True)
ch2 = nilchan # rebind ch2 to nil channel
_, _rx = select( _, _rx = select(
ch1.recv, # 0 ch1.recv, # 0
ch2.recv_, # 1 ch1.recv_, # 1
(ch2.send, obj2), # 2 (ch1.send, obj), # 2
default, # 3 ch2.recv, # 3
default, # 4
) )
if _ == 0: if _ == 0:
# _rx is what was received from ch1 # _rx is what was received from ch1
... ...
if _ == 1: if _ == 1:
# _rx is (rx, ok) of what was received from ch2 # _rx is (rx, ok) of what was received from ch1
... ...
if _ == 2: if _ == 2:
# we know obj2 was sent to ch2 # we know obj was sent to ch1
... ...
if _ == 3: if _ == 3:
# this case will be never selected because
# send/recv on nil channel block forever.
...
if _ == 4:
# default case # default case
... ...
......
...@@ -30,7 +30,7 @@ ...@@ -30,7 +30,7 @@
__version__ = "0.0.0.dev8" __version__ = "0.0.0.dev8"
__all__ = ['go', 'chan', 'select', 'default', 'defer', 'panic', 'recover', 'func', 'gimport'] __all__ = ['go', 'chan', 'select', 'default', 'nilchan', 'defer', 'panic', 'recover', 'func', 'gimport']
from golang._gopath import gimport # make gimport available from golang from golang._gopath import gimport # make gimport available from golang
import inspect, threading, collections, random, sys import inspect, threading, collections, random, sys
...@@ -332,6 +332,9 @@ class chan(object): ...@@ -332,6 +332,9 @@ class chan(object):
# #
# .send(obj) # .send(obj)
def send(self, obj): def send(self, obj):
if self is nilchan:
_blockforever()
self._mu.acquire() self._mu.acquire()
if 1: if 1:
ok = self._trysend(obj) ok = self._trysend(obj)
...@@ -356,6 +359,9 @@ class chan(object): ...@@ -356,6 +359,9 @@ class chan(object):
# #
# .recv_() -> (rx, ok) # .recv_() -> (rx, ok)
def recv_(self): def recv_(self):
if self is nilchan:
_blockforever()
self._mu.acquire() self._mu.acquire()
if 1: if 1:
rx_, ok = self._tryrecv() rx_, ok = self._tryrecv()
...@@ -449,6 +455,9 @@ class chan(object): ...@@ -449,6 +455,9 @@ class chan(object):
# close closes sending side of the channel. # close closes sending side of the channel.
def close(self): def close(self):
if self is nilchan:
panic("close of nil channel")
recvv = [] recvv = []
sendv = [] sendv = []
...@@ -481,6 +490,18 @@ class chan(object): ...@@ -481,6 +490,18 @@ class chan(object):
def __len__(self): def __len__(self):
return len(self._dataq) return len(self._dataq)
def __repr__(self):
if self is nilchan:
return "nilchan"
else:
return super(chan, self).__repr__()
# nilchan is the nil channel.
#
# On nil channel: send/recv block forever; close panics.
nilchan = chan(None) # TODO -> <chan*>(NULL) after move to Cython
# default represents default case for select. # default represents default case for select.
default = object() default = object()
...@@ -523,9 +544,6 @@ if six.PY2: ...@@ -523,9 +544,6 @@ if six.PY2:
# # default case # # default case
# ... # ...
def select(*casev): def select(*casev):
# XXX select on nil chan?
# XXX select{} -> block forever
# select promise: if multiple cases are ready - one will be selected randomly # select promise: if multiple cases are ready - one will be selected randomly
ncasev = list(enumerate(casev)) ncasev = list(enumerate(casev))
random.shuffle(ncasev) random.shuffle(ncasev)
...@@ -550,6 +568,7 @@ def select(*casev): ...@@ -550,6 +568,7 @@ def select(*casev):
panic("select: send expected: %r" % (send,)) panic("select: send expected: %r" % (send,))
ch = send.__self__ ch = send.__self__
if ch is not nilchan: # nil chan is never ready
ch._mu.acquire() ch._mu.acquire()
if 1: if 1:
ok = ch._trysend(tx) ok = ch._trysend(tx)
...@@ -572,6 +591,7 @@ def select(*casev): ...@@ -572,6 +591,7 @@ def select(*casev):
panic("select: recv expected: %r" % (recv,)) panic("select: recv expected: %r" % (recv,))
ch = recv.__self__ ch = recv.__self__
if ch is not nilchan: # nil chan is never ready
ch._mu.acquire() ch._mu.acquire()
if 1: if 1:
rx_, ok = ch._tryrecv() rx_, ok = ch._tryrecv()
...@@ -588,6 +608,10 @@ def select(*casev): ...@@ -588,6 +608,10 @@ def select(*casev):
if ndefault is not None: if ndefault is not None:
return ndefault, None return ndefault, None
# select{} or with nil-channels only -> block forever
if len(recvv) + len(sendv) == 0:
_blockforever()
# second pass: subscribe and wait on all rx/tx cases # second pass: subscribe and wait on all rx/tx cases
g = _WaitGroup() g = _WaitGroup()
...@@ -660,3 +684,13 @@ def select(*casev): ...@@ -660,3 +684,13 @@ def select(*casev):
finally: finally:
# unsubscribe not-succeeded waiters # unsubscribe not-succeeded waiters
g.dequeAll() g.dequeAll()
# _blockforever blocks current goroutine forever.
def _blockforever():
# take a lock twice. It will forever block on the second lock attempt.
# Under gevent, similarly to Go, this raises "LoopExit: This operation
# would block forever", if there are no other greenlets scheduled to be run.
dead = threading.Lock()
dead.acquire()
dead.acquire()
...@@ -18,11 +18,12 @@ ...@@ -18,11 +18,12 @@
# See COPYING file for full licensing terms. # See COPYING file for full licensing terms.
# See https://www.nexedi.com/licensing for rationale and options. # See https://www.nexedi.com/licensing for rationale and options.
from golang import go, chan, select, default, _PanicError, func, panic, defer, recover from golang import go, chan, select, default, nilchan, _PanicError, func, panic, defer, recover
from pytest import raises from pytest import raises
from os.path import dirname from os.path import dirname
import os, sys, time, threading, inspect, subprocess import os, sys, time, threading, inspect, subprocess
import golang
from golang import _chan_recv, _chan_send from golang import _chan_recv, _chan_send
from golang._pycompat import im_class from golang._pycompat import im_class
...@@ -313,6 +314,50 @@ def test_select(): ...@@ -313,6 +314,50 @@ def test_select():
assert len(ch2._sendq) == len(ch2._recvq) == 0 assert len(ch2._sendq) == len(ch2._recvq) == 0
# blocking send + nil channel
z = nilchan
for i in range(N):
ch = chan()
done = chan()
def _():
waitBlocked(ch.send)
assert len(z._sendq) == len(z._recvq) == 0
assert ch.recv() == 'c'
done.close()
go(_)
_, _rx = select(
z.recv,
(z.send, 0),
(ch.send, 'c'),
)
assert (_, _rx) == (2, None)
done.recv()
assert len(ch._sendq) == len(ch._recvq) == 0
# blocking recv + nil channel
for i in range(N):
ch = chan()
done = chan()
def _():
waitBlocked(ch.recv)
assert len(z._sendq) == len(z._recvq) == 0
ch.send('d')
done.close()
go(_)
_, _rx = select(
z.recv,
(z.send, 0),
ch.recv,
)
assert (_, _rx) == (2, 'd')
done.recv()
assert len(ch._sendq) == len(ch._recvq) == 0
# buffered ping-pong # buffered ping-pong
ch = chan(1) ch = chan(1)
for i in range(N): for i in range(N):
...@@ -406,6 +451,33 @@ def test_select(): ...@@ -406,6 +451,33 @@ def test_select():
assert len(ch2._sendq) == len(ch2._recvq) == 0 assert len(ch2._sendq) == len(ch2._recvq) == 0
# BlocksForever is used in "blocks forever" tests where golang._blockforever
# is patched to raise instead of block.
class BlocksForever(Exception):
pass
def test_blockforever():
B = golang._blockforever
def _(): raise BlocksForever()
golang._blockforever = _
try:
_test_blockforever()
finally:
golang._blockforever = B
def _test_blockforever():
z = nilchan
with raises(BlocksForever): z.send(0)
with raises(BlocksForever): z.recv()
with raises(_PanicError): z.close() # to fully cover nilchan ops
# select{} & nil-channel only
with raises(BlocksForever): select()
with raises(BlocksForever): select((z.send, 0))
with raises(BlocksForever): select(z.recv)
with raises(BlocksForever): select((z.send, 1), z.recv)
def test_method(): def test_method():
# test how @func(cls) works # test how @func(cls) works
# this also implicitly tests just @func, since @func(cls) uses that. # this also implicitly tests just @func, since @func(cls) uses that.
......
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