use someone else's interprocess locking code instead of python locks/semaphores - needs testing in Linux

pyfpdb/fpdb.py

@@ -34,6 +34,8 @@ import pygtk
 pygtk.require('2.0')
 import gtk
 
+import interlocks
+
 
 import fpdb_simple
 import GuiBulkImport
@@ -503,7 +505,8 @@ This program is licensed under the AGPL3, see docs"""+os.sep+"agpl-3.0.txt")
 
     def __init__(self):
         self.threads = []
-        self.lock = threading.Lock()
+        # no more than 1 process can this lock at a time:
+        self.lock = interlocks.InterProcessLock(name="fpdb_global_lock")
         self.db = None
         self.status_bar = None
 

pyfpdb/interlocks.py

@@ -0,0 +1,271 @@
+
+# Code from http://ender.snowburst.org:4747/~jjohns/interlocks.py
+# Thanks JJ!
+
+import sys
+import os, os.path
+import subprocess
+import time
+import signal
+import base64
+
+InterProcessLock = None
+
+"""
+Just use me like a thread lock.  acquire() / release() / locked()
+
+Differences compared to thread locks:
+1. By default, acquire()'s wait parameter is false.
+2. When acquire fails, SingleInstanceError is thrown instead of simply returning false.
+3. acquire() can take a 3rd parameter retry_time, which, if wait is True, tells the locking 
+   mechanism how long to sleep between retrying the lock.  Has no effect for unix/InterProcessLockFcntl.
+
+Differences in fpdb version to JJ's original:
+1. Changed acquire() to return false like other locks
+2. Made acquire fail if same process already has the lock
+"""
+
+class SingleInstanceError(RuntimeError):
+    "Thrown when you try to acquire an InterProcessLock and another version of the process is already running."
+
+class InterProcessLockBase:
+    def __init__(self, name=None ):
+        self._has_lock = False
+        if not name:
+            name = sys.argv[0]
+        self.name = name
+
+    def getHashedName(self):
+        return base64.b64encode(self.name).replace('=','')
+
+    def acquire_impl(self, wait): abstract
+        
+    def acquire(self, wait=False, retry_time=1):
+        if self._has_lock:             # make sure 2nd acquire in same process fails
+            return False
+        while not self._has_lock:
+            try:
+                self.acquire_impl(wait)
+                self._has_lock = True
+                #print 'i have the lock'
+            except SingleInstanceError:
+                if not wait:
+                    # raise            # change back to normal acquire functionality, sorry JJ!
+                    return False
+                time.sleep(retry_time)
+        return True
+
+    def release(self):
+        self.release_impl()
+        self._has_lock = False
+
+    def locked(self):
+        if self._has_lock:
+            return True
+        try:
+            self.acquire()
+            self.release()
+            return False
+        except SingleInstanceError:
+            return True    
+
+LOCK_FILE_DIRECTORY = '/tmp'
+
+class InterProcessLockFcntl(InterProcessLockBase):
+    def __init__(self, name=None):
+        InterProcessLockBase.__init__(self, name)
+        self.lockfd = 0
+        self.lock_file_name = os.path.join(LOCK_FILE_DIRECTORY, self.getHashedName() + '.lck')
+        assert(os.path.isdir(LOCK_FILE_DIRECTORY))
+
+    # This is the suggested way to get a safe file name, but I like having a descriptively named lock file.
+    def getHashedName(self):
+        import re
+        bad_filename_character_re = re.compile(r'/\?<>\\\:;\*\|\'\"\^=\.\[\]')
+        return bad_filename_character_re.sub('_',self.name)
+
+    def acquire_impl(self, wait):
+        self.lockfd = open(self.lock_file_name, 'w')
+        fcntrl_options = fcntl.LOCK_EX
+        if not wait:
+            fcntrl_options |= fcntl.LOCK_NB
+        try:
+            fcntl.flock(self.lockfd, fcntrl_options)
+        except IOError:
+            self.lockfd.close()
+            self.lockfd = 0
+            raise SingleInstanceError('Could not acquire exclusive lock on '+self.lock_file_name)
+            
+    def release_impl(self):
+        fcntl.lockf(self.lockfd, fcntl.LOCK_UN)
+        self.lockfd.close()
+        self.lockfd = 0
+        try:
+            os.unlink(self.lock_file_name)
+        except IOError:
+            # We don't care about the existence of the file too much here.  It's the flock() we care about,
+            # And that should just go away magically.
+            pass
+
+class InterProcessLockWin32(InterProcessLockBase):
+    def __init__(self, name=None):
+        InterProcessLockBase.__init__(self, name)        
+        self.mutex = None
+            
+    def acquire_impl(self,wait):
+        self.mutex = win32event.CreateMutex(None, 0, self.getHashedName())
+        if win32api.GetLastError() == winerror.ERROR_ALREADY_EXISTS:
+            self.mutex.Close()
+            self.mutex = None
+            raise SingleInstanceError('Could not acquire exclusive lock on ' + self.name)
+            
+    def release_impl(self):
+        self.mutex.Close()
+        
+class InterProcessLockSocket(InterProcessLockBase):
+    def __init__(self, name=None):
+        InterProcessLockBase.__init__(self, name)        
+        self.socket = None
+        self.portno = 65530 - abs(self.getHashedName().__hash__()) % 32749
+        
+    def acquire_impl(self, wait):
+        self.socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        try:
+            self.socket.bind(('127.0.0.1', self.portno))
+        except socket.error:
+            self.socket.close()
+            self.socket = None
+            raise SingleInstanceError('Could not acquire exclusive lock on ' + self.name)
+        
+    def release_impl(self):
+        self.socket.close()
+        self.socket = None
+
+# Set InterProcessLock to the correct type given the sysem parameters available
+try:
+    import fcntl
+    InterProcessLock = InterProcessLockFcntl
+except ImportError:
+    try:
+        import win32event
+        import win32api
+        import winerror
+        InterProcessLock = InterProcessLockWin32
+    except ImportError:
+        import socket
+        InterProcessLock = InterProcessLockSocket
+
+def test_construct():
+    """
+    # Making the name of the test unique so it can be executed my multiple users on the same machine.
+    >>> test_name = 'InterProcessLockTest' +str(os.getpid()) + str(time.time())
+
+    >>> lock1 = InterProcessLock(name=test_name)
+    >>> lock1.acquire()
+
+    >>> lock2 = InterProcessLock(name=test_name)
+    >>> lock3 = InterProcessLock(name=test_name)
+
+    # Since lock1 is locked, other attempts to acquire it fail.
+    >>> lock2.acquire()
+    Traceback (most recent call last):
+    ...
+    SingleInstanceError: Could not acquire exclusive lock on /tmp/test.lck
+
+    >>> lock3.acquire()
+    Traceback (most recent call last):
+    ...
+    SingleInstanceError: Could not acquire exclusive lock on /tmp/test.lck
+
+    # Release the lock and let lock2 have it.
+    >>> lock1.release()
+    >>> lock2.acquire()
+
+    >>> lock3.acquire()
+    Traceback (most recent call last):
+    ...
+    SingleInstanceError: Could not acquire exclusive lock on /tmp/test.lck
+
+    # Release it and give it back to lock1
+    >>> lock2.release()
+    >>> lock1.acquire()
+
+    >>> lock2.acquire()
+    Traceback (most recent call last):
+    ...
+    SingleInstanceError: Could not acquire exclusive lock on /tmp/test.lck
+
+    # Test lock status
+    >>> lock2.locked()
+    True
+    >>> lock3.locked()
+    True
+    >>> lock1.locked()
+    True
+
+    >>> lock1.release()
+
+    >>> lock2.locked()
+    False
+    >>> lock3.locked()
+    False
+    >>> lock1.locked()
+    False
+
+    >>> if os.name == 'posix':
+    ...    def os_independent_kill(pid):
+    ...        import signal
+    ...        os.kill(pid, signal.SIGKILL)
+    ... else:
+    ...        assert(os.name == 'nt')
+    ...        def os_independent_kill(pid):
+    ...            ''' http://www.python.org/doc/faq/windows/#how-do-i-emulate-os-kill-in-windows '''
+    ...            import win32api
+    ...            import win32con
+    ...            import pywintypes
+    ...            handle = win32api.OpenProcess(win32con.PROCESS_TERMINATE , pywintypes.FALSE, pid)
+    ...            return (0 != win32api.TerminateProcess(handle, 0))
+
+    # Test to acquire the lock in another process.
+    >>> def execute(cmd):
+    ...    cmd = 'import time;' + cmd + 'time.sleep(10);'
+    ...    process = subprocess.Popen([sys.executable, '-c', cmd])
+    ...    pid = process.pid
+    ...    time.sleep(2) # quick hack, but we test synchronization in the end
+    ...    return pid
+
+    >>> pid = execute('import interlocks;a=interlocks.InterProcessLock(name=\\''+test_name+ '\\');a.acquire();')
+
+    >>> lock1.acquire()
+    Traceback (most recent call last):
+    ...
+    SingleInstanceError: Could not acquire exclusive lock on /tmp/test.lck
+
+    >>> os_independent_kill(pid)
+
+    >>> time.sleep(1)
+
+    >>> lock1.acquire()
+    >>> lock1.release()
+
+    # Testing wait
+
+    >>> pid = execute('import interlocks;a=interlocks.InterProcessLock(name=\\''+test_name+ '\\');a.acquire();')
+
+    >>> lock1.acquire()
+    Traceback (most recent call last):
+    ...
+    SingleInstanceError: Could not acquire exclusive lock on /tmp/test.lck
+
+    >>> os_independent_kill(pid)
+
+    >>> lock1.acquire(True)
+    >>> lock1.release()
+
+    """
+    
+    pass
+
+if __name__=='__main__':
+    import doctest
+    doctest.testmod(optionflags=doctest.IGNORE_EXCEPTION_DETAIL)