[Python-checkins] r86992 - in python/branches/release27-maint: Doc/library/io.rst Lib/test/test_io.py Misc/NEWS Modules/_io/bufferedio.c
antoine.pitrou
python-checkins at python.org
Fri Dec 3 20:31:52 CET 2010
Author: antoine.pitrou
Date: Fri Dec 3 20:31:52 2010
New Revision: 86992
Log:
Merged revisions 86981,86984 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/branches/py3k
........
r86981 | antoine.pitrou | 2010-12-03 19:41:39 +0100 (ven., 03 déc. 2010) | 5 lines
Issue #10478: Reentrant calls inside buffered IO objects (for example by
way of a signal handler) now raise a RuntimeError instead of freezing the
current process.
........
r86984 | antoine.pitrou | 2010-12-03 20:14:17 +0100 (ven., 03 déc. 2010) | 3 lines
Add an "advanced topics" section to the io doc.
........
Modified:
python/branches/release27-maint/ (props changed)
python/branches/release27-maint/Doc/library/io.rst
python/branches/release27-maint/Lib/test/test_io.py
python/branches/release27-maint/Misc/NEWS
python/branches/release27-maint/Modules/_io/bufferedio.c
Modified: python/branches/release27-maint/Doc/library/io.rst
==============================================================================
--- python/branches/release27-maint/Doc/library/io.rst (original)
+++ python/branches/release27-maint/Doc/library/io.rst Fri Dec 3 20:31:52 2010
@@ -515,8 +515,8 @@
Buffered Streams
----------------
-In many situations, buffered I/O streams will provide higher performance
-(bandwidth and latency) than raw I/O streams. Their API is also more usable.
+Buffered I/O streams provide a higher-level interface to an I/O device
+than raw I/O does.
.. class:: BytesIO([initial_bytes])
@@ -776,8 +776,72 @@
# .getvalue() will now raise an exception.
output.close()
+
.. class:: IncrementalNewlineDecoder
A helper codec that decodes newlines for universal newlines mode. It
inherits :class:`codecs.IncrementalDecoder`.
+
+Advanced topics
+---------------
+
+Here we will discuss several advanced topics pertaining to the concrete
+I/O implementations described above.
+
+Performance
+^^^^^^^^^^^
+
+Binary I/O
+""""""""""
+
+By reading and writing only large chunks of data even when the user asks
+for a single byte, buffered I/O is designed to hide any inefficiency in
+calling and executing the operating system's unbuffered I/O routines. The
+gain will vary very much depending on the OS and the kind of I/O which is
+performed (for example, on some contemporary OSes such as Linux, unbuffered
+disk I/O can be as fast as buffered I/O). The bottom line, however, is
+that buffered I/O will offer you predictable performance regardless of the
+platform and the backing device. Therefore, it is most always preferable to
+use buffered I/O rather than unbuffered I/O.
+
+Text I/O
+""""""""
+
+Text I/O over a binary storage (such as a file) is significantly slower than
+binary I/O over the same storage, because it implies conversions from
+unicode to binary data using a character codec. This can become noticeable
+if you handle huge amounts of text data (for example very large log files).
+
+:class:`StringIO`, however, is a native in-memory unicode container and will
+exhibit similar speed to :class:`BytesIO`.
+
+Multi-threading
+^^^^^^^^^^^^^^^
+
+:class:`FileIO` objects are thread-safe to the extent that the operating
+system calls (such as ``read(2)`` under Unix) they are wrapping are thread-safe
+too.
+
+Binary buffered objects (instances of :class:`BufferedReader`,
+:class:`BufferedWriter`, :class:`BufferedRandom` and :class:`BufferedRWPair`)
+protect their internal structures using a lock; it is therefore safe to call
+them from multiple threads at once.
+
+:class:`TextIOWrapper` objects are not thread-safe.
+
+Reentrancy
+^^^^^^^^^^
+
+Binary buffered objects (instances of :class:`BufferedReader`,
+:class:`BufferedWriter`, :class:`BufferedRandom` and :class:`BufferedRWPair`)
+are not reentrant. While reentrant calls will not happen in normal situations,
+they can arise if you are doing I/O in a :mod:`signal` handler. If it is
+attempted to enter a buffered object again while already being accessed
+*from the same thread*, then a :exc:`RuntimeError` is raised.
+
+The above implicitly extends to text files, since the :func:`open()`
+function will wrap a buffered object inside a :class:`TextIOWrapper`. This
+includes standard streams and therefore affects the built-in function
+:func:`print()` as well.
+
Modified: python/branches/release27-maint/Lib/test/test_io.py
==============================================================================
--- python/branches/release27-maint/Lib/test/test_io.py (original)
+++ python/branches/release27-maint/Lib/test/test_io.py Fri Dec 3 20:31:52 2010
@@ -2561,12 +2561,50 @@
def test_interrupted_write_text(self):
self.check_interrupted_write("xy", b"xy", mode="w", encoding="ascii")
+ def check_reentrant_write(self, data, **fdopen_kwargs):
+ def on_alarm(*args):
+ # Will be called reentrantly from the same thread
+ wio.write(data)
+ 1/0
+ signal.signal(signal.SIGALRM, on_alarm)
+ r, w = os.pipe()
+ wio = self.io.open(w, **fdopen_kwargs)
+ try:
+ signal.alarm(1)
+ # Either the reentrant call to wio.write() fails with RuntimeError,
+ # or the signal handler raises ZeroDivisionError.
+ with self.assertRaises((ZeroDivisionError, RuntimeError)) as cm:
+ while 1:
+ for i in range(100):
+ wio.write(data)
+ wio.flush()
+ # Make sure the buffer doesn't fill up and block further writes
+ os.read(r, len(data) * 100)
+ exc = cm.exception
+ if isinstance(exc, RuntimeError):
+ self.assertTrue(str(exc).startswith("reentrant call"), str(exc))
+ finally:
+ wio.close()
+ os.close(r)
+
+ def test_reentrant_write_buffered(self):
+ self.check_reentrant_write(b"xy", mode="wb")
+
+ def test_reentrant_write_text(self):
+ self.check_reentrant_write("xy", mode="w", encoding="ascii")
+
+
class CSignalsTest(SignalsTest):
io = io
class PySignalsTest(SignalsTest):
io = pyio
+ # Handling reentrancy issues would slow down _pyio even more, so the
+ # tests are disabled.
+ test_reentrant_write_buffered = None
+ test_reentrant_write_text = None
+
def test_main():
tests = (CIOTest, PyIOTest,
Modified: python/branches/release27-maint/Misc/NEWS
==============================================================================
--- python/branches/release27-maint/Misc/NEWS (original)
+++ python/branches/release27-maint/Misc/NEWS Fri Dec 3 20:31:52 2010
@@ -1,4 +1,3 @@
-:xq
Python News
+++++++++++
@@ -13,6 +12,10 @@
Library
-------
+- Issue #10478: Reentrant calls inside buffered IO objects (for example by
+ way of a signal handler) now raise a RuntimeError instead of freezing the
+ current process.
+
- Issue #10497: Fix incorrect use of gettext in argparse.
- Issue #10464: netrc now correctly handles lines with embedded '#' characters.
Modified: python/branches/release27-maint/Modules/_io/bufferedio.c
==============================================================================
--- python/branches/release27-maint/Modules/_io/bufferedio.c (original)
+++ python/branches/release27-maint/Modules/_io/bufferedio.c Fri Dec 3 20:31:52 2010
@@ -224,6 +224,7 @@
#ifdef WITH_THREAD
PyThread_type_lock lock;
+ volatile long owner;
#endif
Py_ssize_t buffer_size;
@@ -259,17 +260,39 @@
/* These macros protect the buffered object against concurrent operations. */
#ifdef WITH_THREAD
-#define ENTER_BUFFERED(self) \
- if (!PyThread_acquire_lock(self->lock, 0)) { \
- Py_BEGIN_ALLOW_THREADS \
- PyThread_acquire_lock(self->lock, 1); \
- Py_END_ALLOW_THREADS \
+
+static int
+_enter_buffered_busy(buffered *self)
+{
+ if (self->owner == PyThread_get_thread_ident()) {
+ PyObject *r = PyObject_Repr((PyObject *) self);
+ if (r != NULL) {
+ PyErr_Format(PyExc_RuntimeError,
+ "reentrant call inside %s",
+ PyString_AS_STRING(r));
+ Py_DECREF(r);
+ }
+ return 0;
}
+ Py_BEGIN_ALLOW_THREADS
+ PyThread_acquire_lock(self->lock, 1);
+ Py_END_ALLOW_THREADS
+ return 1;
+}
+
+#define ENTER_BUFFERED(self) \
+ ( (PyThread_acquire_lock(self->lock, 0) ? \
+ 1 : _enter_buffered_busy(self)) \
+ && (self->owner = PyThread_get_thread_ident(), 1) )
#define LEAVE_BUFFERED(self) \
- PyThread_release_lock(self->lock);
+ do { \
+ self->owner = 0; \
+ PyThread_release_lock(self->lock); \
+ } while(0);
+
#else
-#define ENTER_BUFFERED(self)
+#define ENTER_BUFFERED(self) 1
#define LEAVE_BUFFERED(self)
#endif
@@ -425,7 +448,8 @@
int r;
CHECK_INITIALIZED(self)
- ENTER_BUFFERED(self)
+ if (!ENTER_BUFFERED(self))
+ return NULL;
r = buffered_closed(self);
if (r < 0)
@@ -438,7 +462,8 @@
/* flush() will most probably re-take the lock, so drop it first */
LEAVE_BUFFERED(self)
res = PyObject_CallMethodObjArgs((PyObject *)self, _PyIO_str_flush, NULL);
- ENTER_BUFFERED(self)
+ if (!ENTER_BUFFERED(self))
+ return NULL;
if (res == NULL) {
goto end;
}
@@ -643,6 +668,7 @@
PyErr_SetString(PyExc_RuntimeError, "can't allocate read lock");
return -1;
}
+ self->owner = 0;
#endif
/* Find out whether buffer_size is a power of 2 */
/* XXX is this optimization useful? */
@@ -669,7 +695,8 @@
CHECK_INITIALIZED(self)
CHECK_CLOSED(self, "flush of closed file")
- ENTER_BUFFERED(self)
+ if (!ENTER_BUFFERED(self))
+ return NULL;
res = _bufferedwriter_flush_unlocked(self, 0);
if (res != NULL && self->readable) {
/* Rewind the raw stream so that its position corresponds to
@@ -696,7 +723,8 @@
return NULL;
}
- ENTER_BUFFERED(self)
+ if (!ENTER_BUFFERED(self))
+ return NULL;
if (self->writable) {
res = _bufferedwriter_flush_unlocked(self, 1);
@@ -731,7 +759,8 @@
if (n == -1) {
/* The number of bytes is unspecified, read until the end of stream */
- ENTER_BUFFERED(self)
+ if (!ENTER_BUFFERED(self))
+ return NULL;
res = _bufferedreader_read_all(self);
LEAVE_BUFFERED(self)
}
@@ -739,7 +768,8 @@
res = _bufferedreader_read_fast(self, n);
if (res == Py_None) {
Py_DECREF(res);
- ENTER_BUFFERED(self)
+ if (!ENTER_BUFFERED(self))
+ return NULL;
res = _bufferedreader_read_generic(self, n);
LEAVE_BUFFERED(self)
}
@@ -767,7 +797,8 @@
if (n == 0)
return PyBytes_FromStringAndSize(NULL, 0);
- ENTER_BUFFERED(self)
+ if (!ENTER_BUFFERED(self))
+ return NULL;
if (self->writable) {
res = _bufferedwriter_flush_unlocked(self, 1);
@@ -823,7 +854,8 @@
/* TODO: use raw.readinto() instead! */
if (self->writable) {
- ENTER_BUFFERED(self)
+ if (!ENTER_BUFFERED(self))
+ return NULL;
res = _bufferedwriter_flush_unlocked(self, 0);
LEAVE_BUFFERED(self)
if (res == NULL)
@@ -867,7 +899,8 @@
goto end_unlocked;
}
- ENTER_BUFFERED(self)
+ if (!ENTER_BUFFERED(self))
+ goto end_unlocked;
/* Now we try to get some more from the raw stream */
if (self->writable) {
@@ -1017,7 +1050,8 @@
}
}
- ENTER_BUFFERED(self)
+ if (!ENTER_BUFFERED(self))
+ return NULL;
/* Fallback: invoke raw seek() method and clear buffer */
if (self->writable) {
@@ -1055,7 +1089,8 @@
return NULL;
}
- ENTER_BUFFERED(self)
+ if (!ENTER_BUFFERED(self))
+ return NULL;
if (self->writable) {
res = _bufferedwriter_flush_unlocked(self, 0);
@@ -1715,7 +1750,10 @@
return NULL;
}
- ENTER_BUFFERED(self)
+ if (!ENTER_BUFFERED(self)) {
+ PyBuffer_Release(&buf);
+ return NULL;
+ }
/* Fast path: the data to write can be fully buffered. */
if (!VALID_READ_BUFFER(self) && !VALID_WRITE_BUFFER(self)) {
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