[PATCH 3 of 7 V2] transaction: add onclose/onabort hook for pre-close logic

[Durham Goode]

# HG changeset patch
# User Durham Goode <durham at fb.com>
# Date 1395701867 25200
#      Mon Mar 24 15:57:47 2014 -0700
# Node ID f85f9ea96d16e180de3e38cfc468e53441f41743
# Parent  a4fddbaf22f873d6d700be4b7d3842457d3680aa
transaction: add onclose/onabort hook for pre-close logic

Adds an optional onclose parameter to transactions that gets called just before
the transaction is committed. This allows things that build up data over the
course of the transaction (like the fncache) to commit their data.

Also adds onabort. It's not used, but will allow extensions to hook into onclose
and onabort to provide transaction support.

diff --git a/mercurial/transaction.py b/mercurial/transaction.py
--- a/mercurial/transaction.py
+++ b/mercurial/transaction.py
@@ -42,12 +42,15 @@
     opener.unlink(journal)
 
 class transaction(object):
-    def __init__(self, report, opener, journal, after=None, createmode=None):
+    def __init__(self, report, opener, journal, after=None, createmode=None,
+            onclose=None, onabort=None):
         self.count = 1
         self.usages = 1
         self.report = report
         self.opener = opener
         self.after = after
+        self.onclose = onclose
+        self.onabort = onabort
         self.entries = []
         self.map = {}
         self.journal = journal
@@ -126,6 +129,9 @@
     @active
     def close(self):
         '''commit the transaction'''
+        if self.count == 1 and self.onclose:
+            self.onclose()
+
         self.count -= 1
         if self.count != 0:
             return
@@ -149,6 +155,9 @@
         self.usages = 0
         self.file.close()
 
+        if self.onabort:
+            self.onabort()
+
         try:
             if not self.entries:
                 if self.journal: