changeset 31956:c13ff31818b0

ui: add special-purpose atexit functionality In spite of its longstanding use, Python's built-in atexit code is not suitable for Mercurial's purposes, for several reasons: * Handlers run after application code has finished. * Because of this, the code that runs handlers swallows exceptions (since there's no possible stacktrace to associate errors with). If we're lucky, we'll get something spat out to stderr (if stderr still works), which of course isn't any use in a big deployment where it's important that exceptions get logged and aggregated. * Mercurial's current atexit handlers make unfortunate assumptions about process state (specifically stdio) that, coupled with the above problems, make it impossible to deal with certain categories of error (try "hg status > /dev/full" on a Linux box). * In Python 3, the atexit implementation is completely hidden, so we can't hijack the platform's atexit code to run handlers at a time of our choosing. As a result, here's a perfectly cromulent atexit-like implementation over which we have control. This lets us decide exactly when the handlers run (after each request has completed), and control what the process state is when that occurs (and afterwards).
author Bryan O'Sullivan <bryano@fb.com>
date Tue, 11 Apr 2017 14:54:12 -0700
parents 4c2c30bc38b4
children 84f9eb9758c0
files mercurial/dispatch.py mercurial/ui.py
diffstat 2 files changed, 31 insertions(+), 0 deletions(-) [+]
line wrap: on
line diff
--- a/mercurial/dispatch.py	Fri Apr 14 08:55:18 2017 +0200
+++ b/mercurial/dispatch.py	Tue Apr 11 14:54:12 2017 -0700
@@ -59,6 +59,23 @@
         self.fout = fout
         self.ferr = ferr
 
+    def _runexithandlers(self):
+        exc = None
+        handlers = self.ui._exithandlers
+        try:
+            while handlers:
+                func, args, kwargs = handlers.pop()
+                try:
+                    func(*args, **kwargs)
+                except: # re-raises below
+                    if exc is None:
+                        exc = sys.exc_info()[1]
+                    self.ui.warn(('error in exit handlers:\n'))
+                    self.ui.traceback(force=True)
+        finally:
+            if exc is not None:
+                raise exc
+
 def run():
     "run the command in sys.argv"
     sys.exit((dispatch(request(pycompat.sysargv[1:])) or 0) & 255)
@@ -146,6 +163,10 @@
             req.ui.log('uiblocked', 'ui blocked ms', **req.ui._blockedtimes)
         req.ui.log("commandfinish", "%s exited %s after %0.2f seconds\n",
                    msg, ret or 0, duration)
+        try:
+            req._runexithandlers()
+        except: # exiting, so no re-raises
+            ret = ret or -1
     return ret
 
 def _runcatch(req):
--- a/mercurial/ui.py	Fri Apr 14 08:55:18 2017 +0200
+++ b/mercurial/ui.py	Tue Apr 11 14:54:12 2017 -0700
@@ -139,6 +139,8 @@
         """
         # _buffers: used for temporary capture of output
         self._buffers = []
+        # _exithandlers: callbacks run at the end of a request
+        self._exithandlers = []
         # 3-tuple describing how each buffer in the stack behaves.
         # Values are (capture stderr, capture subprocesses, apply labels).
         self._bufferstates = []
@@ -163,6 +165,7 @@
         self._styles = {}
 
         if src:
+            self._exithandlers = src._exithandlers
             self.fout = src.fout
             self.ferr = src.ferr
             self.fin = src.fin
@@ -946,6 +949,13 @@
 
         return True
 
+    def atexit(self, func, *args, **kwargs):
+        '''register a function to run after dispatching a request
+
+        Handlers do not stay registered across request boundaries.'''
+        self._exithandlers.append((func, args, kwargs))
+        return func
+
     def interface(self, feature):
         """what interface to use for interactive console features?