https://origsvn.digium.com/svn/asterisk/branches/1.4

........
r108135 | russell | 2008-03-12 14:57:42 -0500 (Wed, 12 Mar 2008) | 40 lines

(closes issue #12187, reported by atis, fixed by me after some brainstorming
 on the issue with mmichelson)

- Update copyright info on app_chanspy.

- Fix a race condition that caused app_chanspy to crash.  The issue was that
  the chanspy datastore magic that was used to ensure that spyee channels did
  not disappear out from under the code did not completely solve the problem.
  It was actually possible for chanspy to acquire a channel reference out of
  its datastore to a channel that was in the middle of being destroyed.  That
  was because datastore destruction in ast_channel_free() was done near the
  end.  So, this left the code in app_chanspy accessing a channel that was
  partially, or completely invalid because it was in the process of being free'd
  by another thread.  The following sort of shows the code path where the race 
  occurred:

  =============================================================================
  Thread 1 (PBX thread for spyee chan)  ||   Thread 2 (chanspy)
  --------------------------------------||-------------------------------------
  ast_channel_free()                    ||
    - remove channel from channel list  ||
    - lock/unlock the channel to ensure ||
      that no references retrieved from ||
      the channel list exist.           ||
  --------------------------------------||-------------------------------------
                                        || channel_spy()
    - destroy some channel data         ||  - Lock chanspy datastore
                                        ||  - Retrieve reference to channel
                                        ||  - lock channel
                                        ||  - Unlock chanspy datastore
  --------------------------------------||-------------------------------------
     - destroy channel datastores       ||
        - call chanspy datastore d'tor  ||  
          which NULL's out the ds'      ||  - Operate on the channel ...
          reference to the channel      ||     
                                        ||
    - free the channel                  || 
                                        ||
                                        ||  - unlock the channel
  --------------------------------------||-------------------------------------
  =============================================================================

........


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@108137 65c4cc65-6c06-0410-ace0-fbb531ad65f3