Fixes Issue #12268 for the io module - File readline, readlines and

read or readall methods no longer lose data when an underlying read
system call is interrupted within an io module object.  IOError is no
longer raised due to a read system call returning EINTR from within
these methods.

This is a backport of changeset 781b95159954 from 3.2.
The earlier 2.7 changeset 67dc99a989cd already fixed this for the
builtin python 2.x file object.

Lib/test/test_file_eintr.py

+# Written to test interrupted system calls interfering with our many buffered
+# IO implementations.  http://bugs.python.org/issue12268
+#
+# This tests the '_io' module.  Similar tests for Python 2.x's older
+# default file I/O implementation exist within test_file2k.py.
+#
+# It was suggested that this code could be merged into test_io and the tests
+# made to work using the same method as the existing signal tests in test_io.
+# I was unable to get single process tests using alarm or setitimer that way
+# to reproduce the EINTR problems.  This process based test suite reproduces
+# the problems prior to the issue12268 patch reliably on Linux and OSX.
+#  - gregory.p.smith
+
+import os
+import select
+import signal
+import subprocess
+import sys
+from test.test_support import run_unittest
+import time
+import unittest
+
+# Test import all of the things we're about to try testing up front.
+from _io import FileIO
+
+
+@unittest.skipUnless(os.name == 'posix', 'tests requires a posix system.')
+class TestFileIOSignalInterrupt(unittest.TestCase):
+    def setUp(self):
+        self._process = None
+
+    def tearDown(self):
+        if self._process and self._process.poll() is None:
+            try:
+                self._process.kill()
+            except OSError:
+                pass
+
+    def _generate_infile_setup_code(self):
+        """Returns the infile = ... line of code for the reader process.
+
+        subclasseses should override this to test different IO objects.
+        """
+        return ('import _io ;'
+                'infile = _io.FileIO(sys.stdin.fileno(), "rb")')
+
+    def fail_with_process_info(self, why, stdout=b'', stderr=b'',
+                               communicate=True):
+        """A common way to cleanup and fail with useful debug output.
+
+        Kills the process if it is still running, collects remaining output
+        and fails the test with an error message including the output.
+
+        Args:
+            why: Text to go after "Error from IO process" in the message.
+            stdout, stderr: standard output and error from the process so
+                far to include in the error message.
+            communicate: bool, when True we call communicate() on the process
+                after killing it to gather additional output.
+        """
+        if self._process.poll() is None:
+            time.sleep(0.1)  # give it time to finish printing the error.
+            try:
+                self._process.terminate()  # Ensure it dies.
+            except OSError:
+                pass
+        if communicate:
+            stdout_end, stderr_end = self._process.communicate()
+            stdout += stdout_end
+            stderr += stderr_end
+        self.fail('Error from IO process %s:\nSTDOUT:\n%sSTDERR:\n%s\n' %
+                  (why, stdout.decode(), stderr.decode()))
+
+    def _test_reading(self, data_to_write, read_and_verify_code):
+        """Generic buffered read method test harness to validate EINTR behavior.
+
+        Also validates that Python signal handlers are run during the read.
+
+        Args:
+            data_to_write: String to write to the child process for reading
+                before sending it a signal, confirming the signal was handled,
+                writing a final newline and closing the infile pipe.
+            read_and_verify_code: Single "line" of code to read from a file
+                object named 'infile' and validate the result.  This will be
+                executed as part of a python subprocess fed data_to_write.
+        """
+        infile_setup_code = self._generate_infile_setup_code()
+        # Total pipe IO in this function is smaller than the minimum posix OS
+        # pipe buffer size of 512 bytes.  No writer should block.
+        assert len(data_to_write) < 512, 'data_to_write must fit in pipe buf.'
+
+        # Start a subprocess to call our read method while handling a signal.
+        self._process = subprocess.Popen(
+                [sys.executable, '-u', '-c',
+                 'import io, signal, sys ;'
+                 'signal.signal(signal.SIGINT, '
+                               'lambda s, f: sys.stderr.write("$\\n")) ;'
+                 + infile_setup_code + ' ;' +
+                 'sys.stderr.write("Worm Sign!\\n") ;'
+                 + read_and_verify_code + ' ;' +
+                 'infile.close()'
+                ],
+                stdin=subprocess.PIPE, stdout=subprocess.PIPE,
+                stderr=subprocess.PIPE)
+
+        # Wait for the signal handler to be installed.
+        worm_sign = self._process.stderr.read(len(b'Worm Sign!\n'))
+        if worm_sign != b'Worm Sign!\n':  # See also, Dune by Frank Herbert.
+            self.fail_with_process_info('while awaiting a sign',
+                                        stderr=worm_sign)
+        self._process.stdin.write(data_to_write)
+
+        signals_sent = 0
+        rlist = []
+        # We don't know when the read_and_verify_code in our child is actually
+        # executing within the read system call we want to interrupt.  This
+        # loop waits for a bit before sending the first signal to increase
+        # the likelihood of that.  Implementations without correct EINTR
+        # and signal handling usually fail this test.
+        while not rlist:
+            rlist, _, _ = select.select([self._process.stderr], (), (), 0.05)
+            self._process.send_signal(signal.SIGINT)
+            signals_sent += 1
+            if signals_sent > 200:
+                self._process.kill()
+                self.fail('reader process failed to handle our signals.')
+        # This assumes anything unexpected that writes to stderr will also
+        # write a newline.  That is true of the traceback printing code.
+        signal_line = self._process.stderr.readline()
+        if signal_line != b'$\n':
+            self.fail_with_process_info('while awaiting signal',
+                                        stderr=signal_line)
+
+        # We append a newline to our input so that a readline call can
+        # end on its own before the EOF is seen and so that we're testing
+        # the read call that was interrupted by a signal before the end of
+        # the data stream has been reached.
+        stdout, stderr = self._process.communicate(input=b'\n')
+        if self._process.returncode:
+            self.fail_with_process_info(
+                    'exited rc=%d' % self._process.returncode,
+                    stdout, stderr, communicate=False)
+        # PASS!
+
+    # String format for the read_and_verify_code used by read methods.
+    _READING_CODE_TEMPLATE = (
+            'got = infile.{read_method_name}() ;'
+            'expected = {expected!r} ;'
+            'assert got == expected, ('
+                    '"{read_method_name} returned wrong data.\\n"'
+                    '"got data %r\\nexpected %r" % (got, expected))'
+            )
+
+    def test_readline(self):
+        """readline() must handle signals and not lose data."""
+        self._test_reading(
+                data_to_write=b'hello, world!',
+                read_and_verify_code=self._READING_CODE_TEMPLATE.format(
+                        read_method_name='readline',
+                        expected=b'hello, world!\n'))
+
+    def test_readlines(self):
+        """readlines() must handle signals and not lose data."""
+        self._test_reading(
+                data_to_write=b'hello\nworld!',
+                read_and_verify_code=self._READING_CODE_TEMPLATE.format(
+                        read_method_name='readlines',
+                        expected=[b'hello\n', b'world!\n']))
+
+    def test_readall(self):
+        """readall() must handle signals and not lose data."""
+        self._test_reading(
+                data_to_write=b'hello\nworld!',
+                read_and_verify_code=self._READING_CODE_TEMPLATE.format(
+                        read_method_name='readall',
+                        expected=b'hello\nworld!\n'))
+        # read() is the same thing as readall().
+        self._test_reading(
+                data_to_write=b'hello\nworld!',
+                read_and_verify_code=self._READING_CODE_TEMPLATE.format(
+                        read_method_name='read',
+                        expected=b'hello\nworld!\n'))
+
+
+class TestBufferedIOSignalInterrupt(TestFileIOSignalInterrupt):
+    def _generate_infile_setup_code(self):
+        """Returns the infile = ... line of code to make a BufferedReader."""
+        return ('infile = io.open(sys.stdin.fileno(), "rb") ;'
+                'import _io ;assert isinstance(infile, _io.BufferedReader)')
+
+    def test_readall(self):
+        """BufferedReader.read() must handle signals and not lose data."""
+        self._test_reading(
+                data_to_write=b'hello\nworld!',
+                read_and_verify_code=self._READING_CODE_TEMPLATE.format(
+                        read_method_name='read',
+                        expected=b'hello\nworld!\n'))
+
+
+class TestTextIOSignalInterrupt(TestFileIOSignalInterrupt):
+    def _generate_infile_setup_code(self):
+        """Returns the infile = ... line of code to make a TextIOWrapper."""
+        return ('infile = io.open(sys.stdin.fileno(), "rt", newline=None) ;'
+                'import _io ;assert isinstance(infile, _io.TextIOWrapper)')
+
+    def test_readline(self):
+        """readline() must handle signals and not lose data."""
+        self._test_reading(
+                data_to_write=b'hello, world!',
+                read_and_verify_code=self._READING_CODE_TEMPLATE.format(
+                        read_method_name='readline',
+                        expected='hello, world!\n'))
+
+    def test_readlines(self):
+        """readlines() must handle signals and not lose data."""
+        self._test_reading(
+                data_to_write=b'hello\r\nworld!',
+                read_and_verify_code=self._READING_CODE_TEMPLATE.format(
+                        read_method_name='readlines',
+                        expected=['hello\n', 'world!\n']))
+
+    def test_readall(self):
+        """read() must handle signals and not lose data."""
+        self._test_reading(
+                data_to_write=b'hello\nworld!',
+                read_and_verify_code=self._READING_CODE_TEMPLATE.format(
+                        read_method_name='read',
+                        expected="hello\nworld!\n"))
+
+
+def test_main():
+    test_cases = [
+            tc for tc in globals().values()
+            if isinstance(tc, type) and issubclass(tc, unittest.TestCase)]
+    run_unittest(*test_cases)
+
+
+if __name__ == '__main__':
+    test_main()

Misc/NEWS

@@ -414,6 +414,11 @@ Library
 Extension Modules
 -----------------
 
+- Issue #12268: File readline, readlines and read or readall methods
+  no longer lose data when an underlying read system call is interrupted
+  within an io module object.  IOError is no longer raised due to a read
+  system call returning EINTR from within these methods.
+
 - Issue #16012: Fix a regression in pyexpat. The parser's UseForeignDTD()
   method doesn't require an argument again.
 

Modules/_io/_iomodule.h

@@ -57,6 +57,11 @@ extern Py_ssize_t _PyIO_find_line_ending(
     int translated, int universal, PyObject *readnl,
     Py_UNICODE *start, Py_UNICODE *end, Py_ssize_t *consumed);
 
+/* Return 1 if an EnvironmentError with errno == EINTR is set (and then
+   clears the error indicator), 0 otherwise.
+   Should only be called when PyErr_Occurred() is true.
+*/
+extern int _PyIO_trap_eintr(void);
 
 #define DEFAULT_BUFFER_SIZE (8 * 1024)  /* bytes */
 

Modules/_io/bufferedio.c

@@ -710,8 +710,8 @@ _buffered_init(buffered *self)
    clears the error indicator), 0 otherwise.
    Should only be called when PyErr_Occurred() is true.
 */
-static int
-_trap_eintr(void)
+int
+_PyIO_trap_eintr(void)
 {
     static PyObject *eintr_int = NULL;
     PyObject *typ, *val, *tb;
@@ -1296,7 +1296,7 @@ _bufferedreader_raw_read(buffered *self, char *start, Py_ssize_t len)
     */
     do {
         res = PyObject_CallMethodObjArgs(self->raw, _PyIO_str_readinto, memobj, NULL);
-    } while (res == NULL && _trap_eintr());
+    } while (res == NULL && _PyIO_trap_eintr());
     Py_DECREF(memobj);
     if (res == NULL)
         return -1;
@@ -1723,7 +1723,7 @@ _bufferedwriter_raw_write(buffered *self, char *start, Py_ssize_t len)
         errno = 0;
         res = PyObject_CallMethodObjArgs(self->raw, _PyIO_str_write, memobj, NULL);
         errnum = errno;
-    } while (res == NULL && _trap_eintr());
+    } while (res == NULL && _PyIO_trap_eintr());
     Py_DECREF(memobj);
     if (res == NULL)
         return -1;

Modules/_io/fileio.c

@@ -570,6 +570,13 @@ fileio_readall(fileio *self)
         if (n == 0)
             break;
         if (n < 0) {
+            if (errno == EINTR) {
+                if (PyErr_CheckSignals()) {
+                    Py_DECREF(result);
+                    return NULL;
+                }
+                continue;
+            }
             if (total > 0)
                 break;
             if (errno == EAGAIN) {

Modules/_io/iobase.c

@@ -468,8 +468,14 @@ iobase_readline(PyObject *self, PyObject *args)
 
         if (has_peek) {
             PyObject *readahead = PyObject_CallMethod(self, "peek", "i", 1);
-            if (readahead == NULL)
+            if (readahead == NULL) {
+                /* NOTE: PyErr_SetFromErrno() calls PyErr_CheckSignals()
+                   when EINTR occurs so we needn't do it ourselves. */
+                if (_PyIO_trap_eintr()) {
+                    continue;
+                }
                 goto fail;
+            }
             if (!PyBytes_Check(readahead)) {
                 PyErr_Format(PyExc_IOError,
                              "peek() should have returned a bytes object, "
@@ -502,8 +508,14 @@ iobase_readline(PyObject *self, PyObject *args)
         }
 
         b = PyObject_CallMethod(self, "read", "n", nreadahead);
-        if (b == NULL)
+        if (b == NULL) {
+            /* NOTE: PyErr_SetFromErrno() calls PyErr_CheckSignals()
+               when EINTR occurs so we needn't do it ourselves. */
+            if (_PyIO_trap_eintr()) {
+                continue;
+            }
             goto fail;
+        }
         if (!PyBytes_Check(b)) {
             PyErr_Format(PyExc_IOError,
                          "read() should have returned a bytes object, "
@@ -811,6 +823,11 @@ rawiobase_readall(PyObject *self, PyObject *args)
         PyObject *data = PyObject_CallMethod(self, "read",
                                              "i", DEFAULT_BUFFER_SIZE);
         if (!data) {
+            /* NOTE: PyErr_SetFromErrno() calls PyErr_CheckSignals()
+               when EINTR occurs so we needn't do it ourselves. */
+            if (_PyIO_trap_eintr()) {
+                continue;
+            }
             Py_DECREF(chunks);
             return NULL;
         }

Modules/_io/textio.c

@@ -1518,8 +1518,14 @@ textiowrapper_read(textio *self, PyObject *args)
         /* Keep reading chunks until we have n characters to return */
         while (remaining > 0) {
             res = textiowrapper_read_chunk(self);
-            if (res < 0)
+            if (res < 0) {
+                /* NOTE: PyErr_SetFromErrno() calls PyErr_CheckSignals()
+                   when EINTR occurs so we needn't do it ourselves. */
+                if (_PyIO_trap_eintr()) {
+                    continue;
+                }
                 goto fail;
+            }
             if (res == 0)  /* EOF */
                 break;
             if (chunks == NULL) {
@@ -1678,8 +1684,14 @@ _textiowrapper_readline(textio *self, Py_ssize_t limit)
         while (!self->decoded_chars ||
                !PyUnicode_GET_SIZE(self->decoded_chars)) {
             res = textiowrapper_read_chunk(self);
-            if (res < 0)
+            if (res < 0) {
+                /* NOTE: PyErr_SetFromErrno() calls PyErr_CheckSignals()
+                   when EINTR occurs so we needn't do it ourselves. */
+                if (_PyIO_trap_eintr()) {
+                    continue;
+                }
                 goto error;
+            }
             if (res == 0)
                 break;
         }