Save and restore errno value around sighandler.

The signal is often received during epoll_wait call, and python code later
checks the value of libc's errno. That value might get tainted by
sighandler, causing errors to be detected after the call (epoll_wait would
return -1 as the call was interrupted by the signal).

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2063 71dcc9de-d417-0410-9af5-da40c76e7ee4

neo/live_debug.py

@@ -17,6 +17,7 @@
 
 import traceback
 import signal
+import ctypes
 import imp
 import neo
 import pdb
@@ -38,14 +39,20 @@ ENABLED = False
 #     SIGUSR2:
 #       Triggers a pdb prompt on process' controlling TTY.
 
+libc = ctypes.cdll.LoadLibrary('libc.so.6')
+errno = ctypes.c_int.in_dll(libc, 'errno')
+
 def decorate(func):
     def decorator(sig, frame):
+        # Save errno value, to restore it after sig handler returns
+        old_errno = errno.value
         try:
             func(sig, frame)
         except:
             # Prevent exception from exiting signal handler, so mistakes in
             # "debug" module don't kill process.
             traceback.print_exc()
+        errno.value = old_errno
 
 @decorate
 def debugHandler(sig, frame):