Raise a different exception when the lock is not available

When the filesystem is read-only or if we have some other
error, there is no need to wait.
Raise a lock.LockUnavailable exception.

mercurial/lock.py

@@ -1,52 +1,59 b''
 # lock.py - simple locking scheme for mercurial
 #
 # Copyright 2005 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms
 # of the GNU General Public License, incorporated herein by reference.
 
-import os, time
+import errno, os, time
 import util
 
-class LockHeld(Exception):
+class LockException(Exception):
+    pass
+class LockHeld(LockException):
+    pass
+class LockUnavailable(LockException):
     pass
 
 class lock(object):
     def __init__(self, file, wait=1, releasefn=None):
         self.f = file
         self.held = 0
         self.wait = wait
         self.releasefn = releasefn
         self.lock()
 
     def __del__(self):
         self.release()
 
     def lock(self):
         while 1:
             try:
                 self.trylock()
                 return 1
             except LockHeld, inst:
                 if self.wait:
                     time.sleep(1)
                     continue
                 raise inst
 
     def trylock(self):
         pid = os.getpid()
         try:
             util.makelock(str(pid), self.f)
             self.held = 1
-        except (OSError, IOError):
-            raise LockHeld(util.readlock(self.f))
+        except (OSError, IOError), why:
+            if why.errno == errno.EEXIST:
+                raise LockHeld(util.readlock(self.f))
+            else:
+                raise LockUnavailable(why)
 
     def release(self):
         if self.held:
             self.held = 0
             if self.releasefn:
                 self.releasefn()
             try:
                 os.unlink(self.f)
             except: pass