From: chris@atlas.onthe.net.au (Chris Dunlop)
Date: 7 Jun 1996 10:31:39 +1000
Subject: [PG95]: Re: Postgres95 bug report

[Snip...]

>Run the SQL-script below.
>The abort statement near the end of the script causes the message
>"WARN:cannot unlink temp_<some_number>"
>
>After the last select-statement the client hangs.

[Snip...]

This looks like the same problem I found and fixed several weeks ago.
The fix went onto the mailing list, but as it's not too large I'll include
it again...

===========================================================================

Hi all,

This is a patch to prevent an endless loop occuring in the Postgres backend
when a 'warning' error condition generates another warning error contition
in the handler code.

A brief summary is:

A warning condition generates a SIGHUP which is caught by the signal handler
which in turn does a long jump to Warn_restart.  Warn_restart then calls
AbortCurrentTransaction() to... well... abort the current transaction.

The situation I was seeing was that within AbortCurrentTransaction() another
warning condition was being generated ('unable to unlink' some temporary
files).  This, of course, generated another SIGHUP etc...

The symptom is that the backend goes into an endless loop, processing these
warning conditions.

This patch prevents a SIGHUP being generated if we're already processing
code within Warn_restart, thus preventing the endless loop.


Congratulations to all who use and develop Postgres!

- --
Chris Dunlop, <chris@onthe.net.au.

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*** src/backend/tcop/postgres.c.dist	Sat Feb 24 11:47:04 1996
- --- src/backend/tcop/postgres.c	Mon Apr 29 16:19:09 1996
***************
*** 107,112 ****
- --- 107,113 ----
  #else
  sigjmp_buf Warn_restart;
  #endif /*defined(WIN32) || defined(PORTNAME_next) */
+ int InWarn;
  
  extern int	NBuffers;
  
***************
*** 1178,1183 ****
- --- 1179,1185 ----
  #else
      if (setjmp(Warn_restart) != 0) {
  #endif /* WIN32 */
+ 	InWarn = 1;
  
  	time(&tim);
  	
***************
*** 1188,1193 ****
- --- 1190,1196 ----
  	
  	AbortCurrentTransaction();
      }
+     InWarn = 0;
      
      /* ----------------
       *	POSTGRES main processing loop begins here
*** src/backend/utils/error/elog.c.dist	Sat Feb 24 12:03:53 1996
- --- src/backend/utils/error/elog.c	Mon Apr 29 15:23:50 1996
***************
*** 150,162 ****
  #endif /* !PG_STANDALONE */
      
      if (lev == WARN) {
  	ProcReleaseSpins(NULL);	/* get rid of spinlocks we hold */
  #ifndef WIN32
! 	kill(getpid(), 1);	/* abort to traffic cop */
! 	pause();
  #else
! 	longjmp(Warn_restart, 1);
  #endif /* WIN32 */
  	/*
  	 * The pause(3) is just to avoid race conditions where the
  	 * thread of control on an MP system gets past here (i.e.,
- --- 150,165 ----
  #endif /* !PG_STANDALONE */
      
      if (lev == WARN) {
+         extern int InWarn;
  	ProcReleaseSpins(NULL);	/* get rid of spinlocks we hold */
+         if (!InWarn) {
  #ifndef WIN32
! 	    kill(getpid(), 1);	/* abort to traffic cop */
! 	    pause();
  #else
! 	    longjmp(Warn_restart, 1);
  #endif /* WIN32 */
+         }
  	/*
  	 * The pause(3) is just to avoid race conditions where the
  	 * thread of control on an MP system gets past here (i.e.,
- -- 
Chris Dunlop    chris@onthe.net.au   Ph +61.3.9347.2222   Fax +61.3.9347.2155

OnTheNet Pty Ltd      ___       _____                                 ,, ,,
255 Nicholson St.   //  // ,,_   //  //_    __   //| //  __  _//_    // //
Carlton  VIC 3053  //  // // // //  // // //--' // |// //--' //     '' ''
Australia          `--'' '' '' ''  '' ''  `--' ''  ''  `--'  `-'   '' ''  tm