hardlink_lockfile: optimize away most link calls

If fstat shows more than one hardlink, then it's extremely unlikely
that the following link call will result in a lock, so optimize away
the wasteful link call and sleep or raise TryAgain.

diff --git a/pym/portage/locks.py b/pym/portage/locks.py
index 980c1c7622e57cd287c506e96a59c7ffd1c968cc..59026e90adce6c6a5d72b03d343f8629f7bb8883 100644 (file)
--- a/pym/portage/locks.py
+++ b/pym/portage/locks.py
@@ -337,8 +337,10 @@ def hardlink_lockfile(lockfilename, max_wait=DeprecationWarning,
                        else:
                                raise
                else:
+                       myfd_st = None
                        try:
-                               if os.fstat(myfd).st_gid != portage_gid:
+                               myfd_st = os.fstat(myfd)
+                               if myfd_st.st_gid != portage_gid:
                                        os.fchown(myfd, -1, portage_gid)
                        except OSError as e:
                                if e.errno not in (errno.ENOENT, errno.ESTALE):
@@ -349,38 +351,47 @@ def hardlink_lockfile(lockfilename, max_wait=DeprecationWarning,
                                        writemsg(_("Group IDs of current user: %s\n") % \
                                                " ".join(str(n) for n in os.getgroups()),
                                                noiselevel=-1)
+                               else:
+                                       # another process has removed the file, so we'll have
+                                       # to create it again
+                                       continue
                        finally:
                                os.close(myfd)
 
-               try:
-                       os.link(lockfilename, myhardlock)
-               except OSError as e:
-                       func_call = "link('%s', '%s')" % (lockfilename, myhardlock)
-                       if e.errno == OperationNotPermitted.errno:
-                               raise OperationNotPermitted(func_call)
-                       elif e.errno == PermissionDenied.errno:
-                               raise PermissionDenied(func_call)
-                       elif e.errno in (errno.ESTALE, errno.ENOENT):
-                               # another process has removed the file, so we'll have
-                               # to create it again
-                               continue
-                       else:
-                               raise
-
-               if hardlink_is_mine(myhardlock, lockfilename):
-                       if out is not None:
-                               out.eend(os.EX_OK)
-                       break
-
-               try:
-                       os.unlink(myhardlock)
-               except OSError as e:
-                       # This should not happen, since the file name of
-                       # myhardlock is unique to our host and PID,
-                       # and the above link() call succeeded.
-                       if e.errno not in (errno.ENOENT, errno.ESTALE):
-                               raise
-                       raise FileNotFound(myhardlock)
+                       # If fstat shows more than one hardlink, then it's extremely
+                       # unlikely that the following link call will result in a lock,
+                       # so optimize away the wasteful link call and sleep or raise
+                       # TryAgain.
+                       if myfd_st is not None and myfd_st.st_nlink < 2:
+                               try:
+                                       os.link(lockfilename, myhardlock)
+                               except OSError as e:
+                                       func_call = "link('%s', '%s')" % (lockfilename, myhardlock)
+                                       if e.errno == OperationNotPermitted.errno:
+                                               raise OperationNotPermitted(func_call)
+                                       elif e.errno == PermissionDenied.errno:
+                                               raise PermissionDenied(func_call)
+                                       elif e.errno in (errno.ESTALE, errno.ENOENT):
+                                               # another process has removed the file, so we'll have
+                                               # to create it again
+                                               continue
+                                       else:
+                                               raise
+                               else:
+                                       if hardlink_is_mine(myhardlock, lockfilename):
+                                               if out is not None:
+                                                       out.eend(os.EX_OK)
+                                               break
+
+                                       try:
+                                               os.unlink(myhardlock)
+                                       except OSError as e:
+                                               # This should not happen, since the file name of
+                                               # myhardlock is unique to our host and PID,
+                                               # and the above link() call succeeded.
+                                               if e.errno not in (errno.ENOENT, errno.ESTALE):
+                                                       raise
+                                               raise FileNotFound(myhardlock)
 
                if flags & os.O_NONBLOCK:
                        raise TryAgain(lockfilename)