Add file locking for history file

sebastinas · sebastinas · commit 0b626d4aeac0 · 2015-01-11T17:51:35.000+01:00
Signed-off-by: Sebastian Ramacher &lt;sebastian+dev@ramacher.at&gt;
diff --git a/bpython/filelock.py b/bpython/filelock.py
@@ -0,0 +1,50 @@
+# The MIT License
+#
+# Copyright (c) 2015 the bpython authors.
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+
+try:
+    import fcntl
+    has_fcntl = True
+except ImportError:
+    has_fcntl = False
+
+
+class FileLock(object):
+    """Simple file locking
+
+    On platforms without fcntl, all operations in this class are no-ops.
+    """
+
+    def __init__(self, fd, mode=fcntl.LOCK_EX):
+        self.fd = fd
+        self.mode = mode
+
+    def __enter__(self):
+        if has_fcntl:
+            fcntl.flock(self.fd, self.mode)
+        return self
+
+    def __exit__(self, *args):
+        if has_fcntl:
+            fcntl.flock(self.fd, fcntl.LOCK_UN)
+
+# vim: sw=4 ts=4 sts=4 ai et
diff --git a/bpython/history.py b/bpython/history.py
@@ -25,6 +25,7 @@
 import os
 
 from bpython.translations import _
+from bpython.filelock import FileLock
 
 
 class History(object):
@@ -173,7 +174,8 @@ def reset(self):
 
     def load(self, filename, encoding):
         with codecs.open(filename, 'r', encoding, 'ignore') as hfile:
-            self.entries = self.load_from(hfile)
+            with FileLock(hfile) as lock:
+                self.entries = self.load_from(hfile)
 
 
     def load_from(self, fd):
@@ -185,7 +187,8 @@ def load_from(self, fd):
 
     def save(self, filename, encoding, lines=0):
         with codecs.open(filename, 'w', encoding, 'ignore') as hfile:
-            self.save_to(hfile, self.entries, lines)
+            with FileLock(hfile) as lock:
+                self.save_to(hfile, self.entries, lines)
 
 
     def save_to(self, fd, entries=None, lines=0):
@@ -202,17 +205,18 @@ def append_reload_and_write(self, s, filename, encoding):
 
         try:
             with codecs.open(filename, 'rw+', encoding, 'ignore') as hfile:
-                # read entries
-                hfile.seek(0, os.SEEK_SET)
-                entries = self.load_from(hfile)
-                self.append_to(entries, s)
-
-                # write new entries
-                hfile.seek(0, os.SEEK_SET)
-                hfile.truncate()
-                self.save_to(hfile, entries, self.hist_size)
-
-                self.entries = entries
+                with FileLock(hfile) as lock:
+                    # read entries
+                    hfile.seek(0, os.SEEK_SET)
+                    entries = self.load_from(hfile)
+                    self.append_to(entries, s)
+
+                    # write new entries
+                    hfile.seek(0, os.SEEK_SET)
+                    hfile.truncate()
+                    self.save_to(hfile, entries, self.hist_size)
+
+                    self.entries = entries
         except EnvironmentError as err:
             raise RuntimeError(_('Error occurded while writing to file %s (%s)')
                                % (filename, err.strerror))
