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#
# Copyright (C) 2016 The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import os
import platform
import select
from Queue import Queue
from threading import Thread
def isWindows():
""" Returns True when running with the native port of Python for Windows,
False when running on any other platform (including the Cygwin port of
Python).
"""
# Note: The cygwin port of Python returns "CYGWIN_NT_xxx"
return platform.system() == "Windows"
class FileDescriptorStreams(object):
""" Platform agnostic abstraction enabling non-blocking I/O over a
collection of file descriptors. This abstraction is required because
fctnl(os.O_NONBLOCK) is not supported on Windows.
"""
@classmethod
def create(cls):
""" Factory method: instantiates the concrete class according to the
current platform.
"""
if isWindows():
return _FileDescriptorStreamsThreads()
else:
return _FileDescriptorStreamsNonBlocking()
def __init__(self):
self.streams = []
def add(self, fd, dest, std_name):
""" Wraps an existing file descriptor as a stream.
"""
self.streams.append(self._create_stream(fd, dest, std_name))
def remove(self, stream):
""" Removes a stream, when done with it.
"""
self.streams.remove(stream)
@property
def is_done(self):
""" Returns True when all streams have been processed.
"""
return len(self.streams) == 0
def select(self):
""" Returns the set of streams that have data available to read.
The returned streams each expose a read() and a close() method.
When done with a stream, call the remove(stream) method.
"""
raise NotImplementedError
def _create_stream(fd, dest, std_name):
""" Creates a new stream wrapping an existing file descriptor.
"""
raise NotImplementedError
class _FileDescriptorStreamsNonBlocking(FileDescriptorStreams):
""" Implementation of FileDescriptorStreams for platforms that support
non blocking I/O.
"""
class Stream(object):
""" Encapsulates a file descriptor """
def __init__(self, fd, dest, std_name):
self.fd = fd
self.dest = dest
self.std_name = std_name
self.set_non_blocking()
def set_non_blocking(self):
import fcntl
flags = fcntl.fcntl(self.fd, fcntl.F_GETFL)
fcntl.fcntl(self.fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)
def fileno(self):
return self.fd.fileno()
def read(self):
return self.fd.read(4096)
def close(self):
self.fd.close()
def _create_stream(self, fd, dest, std_name):
return self.Stream(fd, dest, std_name)
def select(self):
ready_streams, _, _ = select.select(self.streams, [], [])
return ready_streams
class _FileDescriptorStreamsThreads(FileDescriptorStreams):
""" Implementation of FileDescriptorStreams for platforms that don't support
non blocking I/O. This implementation requires creating threads issuing
blocking read operations on file descriptors.
"""
def __init__(self):
super(_FileDescriptorStreamsThreads, self).__init__()
# The queue is shared accross all threads so we can simulate the
# behavior of the select() function
self.queue = Queue(10) # Limit incoming data from streams
def _create_stream(self, fd, dest, std_name):
return self.Stream(fd, dest, std_name, self.queue)
def select(self):
# Return only one stream at a time, as it is the most straighforward
# thing to do and it is compatible with the select() function.
item = self.queue.get()
stream = item.stream
stream.data = item.data
return [stream]
class QueueItem(object):
""" Item put in the shared queue """
def __init__(self, stream, data):
self.stream = stream
self.data = data
class Stream(object):
""" Encapsulates a file descriptor """
def __init__(self, fd, dest, std_name, queue):
self.fd = fd
self.dest = dest
self.std_name = std_name
self.queue = queue
self.data = None
self.thread = Thread(target=self.read_to_queue)
self.thread.daemon = True
self.thread.start()
def close(self):
self.fd.close()
def read(self):
data = self.data
self.data = None
return data
def read_to_queue(self):
""" The thread function: reads everything from the file descriptor into
the shared queue and terminates when reaching EOF.
"""
for line in iter(self.fd.readline, b''):
self.queue.put(_FileDescriptorStreamsThreads.QueueItem(self, line))
self.fd.close()
self.queue.put(_FileDescriptorStreamsThreads.QueueItem(self, None))
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