def __enter__(self):
readable_fh, self.writable_fh = os.pipe()
self.readable = os.fdopen(readable_fh,
'rb' if self.encoding == None else 'rt',
encoding=self.encoding,
errors=self.errors)
self.thread = ExceptionalThread(target=self._writer)
self.thread.start()
return self.readable
def __enter__(self):
self.readable_fh, writable_fh = os.pipe()
self.writable = os.fdopen(writable_fh, 'wb')
self.thread = ExceptionalThread(target=self._reader)
self.thread.start()
return self.writable
class WritablePipe(with_metaclass(ABCMeta, object)):
"""
An object-oriented wrapper for os.pipe. Clients should subclass it, implement
:meth:`.readFrom` to consume the readable end of the pipe, then instantiate the class as a
context manager to get the writable end. See the example below.
>>> import sys, shutil
>>> class MyPipe(WritablePipe):
... def readFrom(self, readable):
... shutil.copyfileobj(codecs.getreader('utf-8')(readable), sys.stdout)
>>> with MyPipe() as writable:
... _ = writable.write('Hello, world!\\n'.encode('utf-8'))
Hello, world!
Each instance of this class creates a thread and invokes the readFrom method in that thread.
The thread will be join()ed upon normal exit from the context manager, i.e. the body of the
`with` statement. If an exception occurs, the thread will not be joined but a well-behaved
:meth:`.readFrom` implementation will terminate shortly thereafter due to the pipe having
been closed.
Now, exceptions in the reader thread will be reraised in the main thread:
>>> class MyPipe(WritablePipe):
... def readFrom(self, readable):
... raise RuntimeError('Hello, world!')
>>> with MyPipe() as writable:
... pass
Traceback (most recent call last):
...
RuntimeError: Hello, world!
More complicated, less illustrative tests:
Same as above, but provving that handles are closed:
>>> x = os.dup(0); os.close(x)
>>> class MyPipe(WritablePipe):
... def readFrom(self, readable):
... raise RuntimeError('Hello, world!')
>>> with MyPipe() as writable:
... pass
Traceback (most recent call last):
...
RuntimeError: Hello, world!
>>> y = os.dup(0); os.close(y); x == y
True
Exceptions in the body of the with statement aren't masked, and handles are closed:
>>> x = os.dup(0); os.close(x)
>>> class MyPipe(WritablePipe):
... def readFrom(self, readable):
... pass
>>> with MyPipe() as writable:
... raise RuntimeError('Hello, world!')
Traceback (most recent call last):
...
RuntimeError: Hello, world!
>>> y = os.dup(0); os.close(y); x == y
True
"""
@abstractmethod
def readFrom(self, readable):
"""
Implement this method to read data from the pipe.
:param file readable: the file object representing the readable end of the pipe. Do not
explicitly invoke the close() method of the object, that will be done automatically.
"""
raise NotImplementedError()
def _reader(self):
with os.fdopen(self.readable_fh, 'rb') as readable:
# FIXME: another race here, causing a redundant attempt to close in the main thread
self.readable_fh = None # signal to parent thread that we've taken over
self.readFrom(readable)
def __init__(self):
super(WritablePipe, self).__init__()
self.readable_fh = None
self.writable = None
self.thread = None
def __enter__(self):
self.readable_fh, writable_fh = os.pipe()
self.writable = os.fdopen(writable_fh, 'wb')
self.thread = ExceptionalThread(target=self._reader)
self.thread.start()
return self.writable
def __exit__(self, exc_type, exc_val, exc_tb):
try:
self.writable.close()
# Closeing the writable end will send EOF to the readable and cause the reader thread
# to finish.
if self.thread is not None:
# reraises any exception that was raised in the thread
self.thread.join()
except:
if exc_type is None:
# Only raise the child exception if there wasn't
# already an exception in the main thread
raise
finally:
# The responsibility for closing the readable end is generally that of the reader
# thread. To cover the small window before the reader takes over we also close it here.
readable_fh = self.readable_fh
if readable_fh is not None:
# FIXME: This is still racy. The reader thread could close it now, and someone
# else may immediately open a new file, reusing the file handle.
os.close(readable_fh)
class ReadablePipe(with_metaclass(ABCMeta, object)):
"""
An object-oriented wrapper for os.pipe. Clients should subclass it, implement
:meth:`.writeTo` to place data into the writable end of the pipe, then instantiate the class
as a context manager to get the writable end. See the example below.
>>> import sys, shutil
>>> class MyPipe(ReadablePipe):
... def writeTo(self, writable):
... writable.write('Hello, world!\\n'.encode('utf-8'))
>>> with MyPipe() as readable:
... shutil.copyfileobj(codecs.getreader('utf-8')(readable), sys.stdout)
Hello, world!
Each instance of this class creates a thread and invokes the :meth:`.writeTo` method in that
thread. The thread will be join()ed upon normal exit from the context manager, i.e. the body
of the `with` statement. If an exception occurs, the thread will not be joined but a
well-behaved :meth:`.writeTo` implementation will terminate shortly thereafter due to the
pipe having been closed.
Now, exceptions in the reader thread will be reraised in the main thread:
>>> class MyPipe(ReadablePipe):
... def writeTo(self, writable):
... raise RuntimeError('Hello, world!')
>>> with MyPipe() as readable:
... pass
Traceback (most recent call last):
...
RuntimeError: Hello, world!
More complicated, less illustrative tests:
Same as above, but provving that handles are closed:
>>> x = os.dup(0); os.close(x)
>>> class MyPipe(ReadablePipe):
... def writeTo(self, writable):
... raise RuntimeError('Hello, world!')
>>> with MyPipe() as readable:
... pass
Traceback (most recent call last):
...
RuntimeError: Hello, world!
>>> y = os.dup(0); os.close(y); x == y
True
Exceptions in the body of the with statement aren't masked, and handles are closed:
>>> x = os.dup(0); os.close(x)
>>> class MyPipe(ReadablePipe):
... def writeTo(self, writable):
... pass
>>> with MyPipe() as readable:
... raise RuntimeError('Hello, world!')
Traceback (most recent call last):
...
RuntimeError: Hello, world!
>>> y = os.dup(0); os.close(y); x == y
True
"""
@abstractmethod
def writeTo(self, writable):
"""
Implement this method to read data from the pipe.
:param file writable: the file object representing the writable end of the pipe. Do not
explicitly invoke the close() method of the object, that will be done automatically.
"""
raise NotImplementedError()
def _writer(self):
try:
with os.fdopen(self.writable_fh, 'wb') as writable:
self.writeTo(writable)
except IOError as e:
# The other side of the pipe may have been closed by the
# reading thread, which is OK.
if e.errno != errno.EPIPE:
raise
def __init__(self):
super(ReadablePipe, self).__init__()
self.writable_fh = None
self.readable = None
self.thread = None
def __enter__(self):
readable_fh, self.writable_fh = os.pipe()
self.readable = os.fdopen(readable_fh, 'rb')
self.thread = ExceptionalThread(target=self._writer)
self.thread.start()
return self.readable
def __exit__(self, exc_type, exc_val, exc_tb):
# Close the read end of the pipe. The writing thread may
# still be writing to the other end, but this will wake it up
# if that's the case.
self.readable.close()
try:
if self.thread is not None:
# reraises any exception that was raised in the thread
self.thread.join()
except:
if exc_type is None:
# Only raise the child exception if there wasn't
# already an exception in the main thread
raise
def startStats(self, preemptable):
thread = ExceptionalThread(target=self._gatherStats,
args=[preemptable])
thread.start()
self.statsThreads.append(thread)
class WritablePipe(ABC):
"""
An object-oriented wrapper for os.pipe. Clients should subclass it, implement
:meth:`.readFrom` to consume the readable end of the pipe, then instantiate the class as a
context manager to get the writable end. See the example below.
>>> import sys, shutil
>>> class MyPipe(WritablePipe):
... def readFrom(self, readable):
... shutil.copyfileobj(codecs.getreader('utf-8')(readable), sys.stdout)
>>> with MyPipe() as writable:
... _ = writable.write('Hello, world!\\n'.encode('utf-8'))
Hello, world!
Each instance of this class creates a thread and invokes the readFrom method in that thread.
The thread will be join()ed upon normal exit from the context manager, i.e. the body of the
`with` statement. If an exception occurs, the thread will not be joined but a well-behaved
:meth:`.readFrom` implementation will terminate shortly thereafter due to the pipe having
been closed.
Now, exceptions in the reader thread will be reraised in the main thread:
>>> class MyPipe(WritablePipe):
... def readFrom(self, readable):
... raise RuntimeError('Hello, world!')
>>> with MyPipe() as writable:
... pass
Traceback (most recent call last):
...
RuntimeError: Hello, world!
More complicated, less illustrative tests:
Same as above, but proving that handles are closed:
>>> x = os.dup(0); os.close(x)
>>> class MyPipe(WritablePipe):
... def readFrom(self, readable):
... raise RuntimeError('Hello, world!')
>>> with MyPipe() as writable:
... pass
Traceback (most recent call last):
...
RuntimeError: Hello, world!
>>> y = os.dup(0); os.close(y); x == y
True
Exceptions in the body of the with statement aren't masked, and handles are closed:
>>> x = os.dup(0); os.close(x)
>>> class MyPipe(WritablePipe):
... def readFrom(self, readable):
... pass
>>> with MyPipe() as writable:
... raise RuntimeError('Hello, world!')
Traceback (most recent call last):
...
RuntimeError: Hello, world!
>>> y = os.dup(0); os.close(y); x == y
True
"""
@abstractmethod
def readFrom(self, readable):
"""
Implement this method to read data from the pipe. This method should support both
binary and text mode output.
:param file readable: the file object representing the readable end of the pipe. Do not
explicitly invoke the close() method of the object, that will be done automatically.
"""
raise NotImplementedError()
def _reader(self):
with os.fdopen(self.readable_fh, 'rb') as readable:
# TODO: If the reader somehow crashes here, both threads might try
# to close readable_fh. Fortunately we don't do anything that
# should be able to fail here.
self.readable_fh = None # signal to parent thread that we've taken over
self.readFrom(readable)
self.reader_done = True
def __init__(self, encoding=None, errors=None):
"""
The specified encoding and errors apply to the writable end of the pipe.
:param str encoding: the name of the encoding used to encode the file. Encodings are the same
as for encode(). Defaults to None which represents binary mode.
:param str errors: an optional string that specifies how encoding errors are to be handled. Errors
are the same as for open(). Defaults to 'strict' when an encoding is specified.
"""
super(WritablePipe, self).__init__()
self.encoding = encoding
self.errors = errors
self.readable_fh = None
self.writable = None
self.thread = None
self.reader_done = False
def __enter__(self):
self.readable_fh, writable_fh = os.pipe()
self.writable = os.fdopen(writable_fh,
'wb' if self.encoding == None else 'wt',
encoding=self.encoding,
errors=self.errors)
self.thread = ExceptionalThread(target=self._reader)
self.thread.start()
return self.writable
def __exit__(self, exc_type, exc_val, exc_tb):
# Closeing the writable end will send EOF to the readable and cause the reader thread
# to finish.
# TODO: Can close() fail? If so, whould we try and clean up after the reader?
self.writable.close()
try:
if self.thread is not None:
# reraises any exception that was raised in the thread
self.thread.join()
except Exception as e:
if exc_type is None:
# Only raise the child exception if there wasn't
# already an exception in the main thread
raise
else:
log.error(
'Swallowing additional exception in reader thread: %s',
str(e))
finally:
# The responsibility for closing the readable end is generally that of the reader
# thread. To cover the small window before the reader takes over we also close it here.
readable_fh = self.readable_fh
if readable_fh is not None:
# Close the file handle. The reader thread must be dead now.
os.close(readable_fh)