blackbox: avoid creating multiple file handles for a single log

blackbox: avoid creating multiple file handles for a single log

There are multiple ui objects in Mercurial that can relate to a repository,
before this change, each one would have its own file pointer, which
results in unfortunate logging behavior.

Also, any log rotation results would be bad because only the
active blackboxui object's file pointer would be refreshed.

Note that this does not prevent two long running hg commands for the same
repository from causing problems.

--- a/hgext/blackbox.py	Wed Feb 24 20:04:32 2016 +0000
+++ b/hgext/blackbox.py	Wed Feb 03 15:41:31 2016 +0000
@@ -49,6 +49,21 @@
 testedwith = 'internal'
 lastblackbox = None
 
+filehandles = {}
+
+def _openlog(vfs):
+    path = vfs.join('blackbox.log')
+    if path in filehandles:
+        return filehandles[path]
+    filehandles[path] = fp = vfs('blackbox.log', 'a')
+    return fp
+
+def _closelog(vfs):
+    path = vfs.join('blackbox.log')
+    fp = filehandles[path]
+    del filehandles[path]
+    fp.close()
+
 def wrapui(ui):
     class blackboxui(ui.__class__):
         @util.propertycache
@@ -71,20 +86,20 @@
                         self.debug("warning: cannot rename '%s' to '%s': %s\n" %
                                    (newpath, oldpath, err.strerror))
 
-            fp = self._bbvfs('blackbox.log', 'a')
+            fp = _openlog(self._bbvfs)
             maxsize = self.configbytes('blackbox', 'maxsize', 1048576)
             if maxsize > 0:
                 st = self._bbvfs.fstat(fp)
                 if st.st_size >= maxsize:
                     path = fp.name
-                    fp.close()
+                    _closelog(self._bbvfs)
                     maxfiles = self.configint('blackbox', 'maxfiles', 7)
                     for i in xrange(maxfiles - 1, 1, -1):
                         rotate(oldpath='%s.%d' % (path, i - 1),
                                newpath='%s.%d' % (path, i))
                     rotate(oldpath=path,
                            newpath=maxfiles > 0 and path + '.1')
-                    fp = self._bbvfs('blackbox.log', 'a')
+                    fp = _openlog(self._bbvfs)
             return fp
 
         def log(self, event, *msg, **opts):