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From: jeff@fluke.UUCP (Jeff Stearns)
Newsgroups: net.bugs.4bsd
Subject: Awk doesn't wait for child processes
Message-ID: <2120@vax4.fluke.UUCP>
Date: Wed, 30-Jan-85 18:07:19 EST
Article-I.D.: vax4.2120
Posted: Wed Jan 30 18:07:19 1985
Date-Received: Sat, 2-Feb-85 00:38:13 EST
Organization: John Fluke Mfg. Co., Inc., Everett, WA
Lines: 116

e shell scripts to fail in mysterious and
	non-deterministic ways.
Repeat-By:
	Arrange for awk to pipe some data to a slow-running process such as sort.
	When awk is finished, it will exit without waiting for its child:

		</etc/passwd awk '{ print $0 | "sort" }' >/tmp/awkout
		# Now note that the size changes as sort continues to run:
		wc /tmp/awkout
		wc /tmp/awkout
		wc /tmp/awkout
		wc /tmp/awkout
Fix:
	My previous bug report included a bogus bug fix which would fail
	under some race conditions.  Here is a proper bug fix which works.
	Two files are affected: main.c and run.c:


*** main.c.old	Wed Jan 30 14:47:01 1985
--- main.c	Wed Jan 30 14:45:27 1985
***************
*** 89,94
  		exit(0);
  	}
  	run();
  	exit(errorflag);
  }
  

--- 89,102 -----
  		exit(0);
  	}
  	run();
+ 	/*
+ 	 *  Awk may have spawned some children (printf "....." | sort).
+ 	 *  The children may still be alive (sort can be quite slow).
+ 	 *  It is a bad idea to exit before our children have completed,
+ 	 *  as the next command to be executed may depend on ALL of our
+ 	 *  processing being complete.  Thus we wait for our kids.
+ 	 */
+ 	WaitForChildren();
  	exit(errorflag);
  }

*** run.c.old	Wed Jan 30 14:47:21 1985
--- run.c	Wed Jan 30 14:45:50 1985
***************
*** 13,18
  {
  	FILE *fp;
  	char *fname;
  } files[FILENUM];
  FILE *popen();
  

--- 13,19 -----
  {
  	FILE *fp;
  	char *fname;
+ 	 int CreatedByPopen;
  } files[FILENUM];
  FILE *popen();
  
***************
*** 858,863
  	if (i >= FILENUM)
  		error(FATAL, "too many output files %d", i);
  	if (a == '|')	/* a pipe! */
  		files[i].fp = popen(x.optr->sval, "w");
  	else if (a == APPEND)
  		files[i].fp = fopen(x.optr->sval, "a");

--- 859,865 -----
  	if (i >= FILENUM)
  		error(FATAL, "too many output files %d", i);
  	if (a == '|')	/* a pipe! */
+ 		files[i].CreatedByPopen = 1,   /* so we remember to pclose it */
  		files[i].fp = popen(x.optr->sval, "w");
  	else if (a == APPEND)
  		files[i].fp = fopen(x.optr->sval, "a");
***************
*** 872,875
  	fflush(files[i].fp);	/* in case someone is waiting for the output */
  #endif
  	tempfree(x);
  }

--- 874,894 -----
  	fflush(files[i].fp);	/* in case someone is waiting for the output */
  #endif
  	tempfree(x);
+ }
+ 
+ /*
+  *  Awk may have spawned some children (printf "....." | sort).
+  *  The children may still be alive (sort can be quite slow).
+  *  It is a bad idea to exit before our children have completed,
+  *  as the next command to be executed may depend on ALL of our
+  *  processing being complete.  Thus we wait for our kids.
+  */
+ WaitForChildren () {
+     int i;
+     for (i=0; i<FILENUM; i++) {
+ 	if (files[i].fp  && files[i].CreatedByPopen) {
+ 	    (void) pclose (files[i].fp);
+ 	    files[i].fp = 0;
+ 	}
+     }
  }
-- 
	Jeff Stearns       (206) 356-5064
	John Fluke Mfg. Co.
	P.O. Box C9090  Everett WA  98043  
	{uw-beaver,decvax!microsof,ucbvax!lbl-csam,allegra,ssc-vax}!fluke!jeff