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Date: Mon, 18 Apr 2011 13:43:31 +0200
From: Peter Rosin <peda AT lysator DOT liu DOT se>
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To: cygwin AT cygwin DOT com
Subject: Memory leak in select.
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Hi!

Using the following STC, I'm seeing what appears to be a memory
leak in select(2).

----------------8<---(selectleak.c)---------
#include <sys/time.h>
#include <fcntl.h>
#include <stdlib.h>

int
main(void)
{
	fd_set fdset;
	struct timeval tv;

	long flags = fcntl(0, F_GETFL);
	fcntl(0, F_SETFL, flags | O_NONBLOCK);

	for (;;) {
		int res;
		char buf[20];

		FD_ZERO(&fdset);
		FD_SET(0, &fdset);
		tv.tv_sec = 1;
		tv.tv_usec = 0;
		res = select(1, &fdset, NULL, NULL, &tv);
		if (res < 0)
			exit(1);
		if (!res)
			continue;
		res = read(0, buf, sizeof(buf));
		if (res < 0)
			exit(1);
	}

	return 0;
}
----------------8<--------------------------

$ gcc -o selectleak selectleak.c
$ cat /dev/zero | ./selectleak

Note that "./selectleak < /dev/zero" does not trigger the leak for me (I haven't
seen the memory usage go up, so at least not as reliably).

An "strace -m malloc,select" has this:

  156   59281 [main] selectleak 8440 cygwin_select: 1, 0x23CCFC, 0x0, 0x0, 0x0
   64   59345 [main] selectleak 8440 calloc: (1, 44) = 49AF58, called by 61002389
   63   59408 [main] selectleak 8440 calloc: (1, 12) = 49B018, called by 61002389
  111   59519 [main] selectleak 8440 cygwin_select: to NULL, ms FFFFFFFF
   62   59581 [main] selectleak 8440 cygwin_select: sel.always_ready 0
  138   59719 [select_pipe] selectleak 8440 peek_pipe: , ready for read: avail 130892
  160   59879 [main] selectleak 8440 select_stuff::wait: woke up.  wait_ret 1.  verifying
   57   59936 [main] selectleak 8440 set_bits: me 0x49AF58, testing fd 0 ()
   62   59998 [main] selectleak 8440 set_bits: ready 1
   62   60060 [main] selectleak 8440 select_stuff::wait: gotone 1
   61   60121 [main] selectleak 8440 select_stuff::wait: returning 0
   61   60182 [main] selectleak 8440 select_stuff::cleanup: calling cleanup routines
  104   60286 [main] selectleak 8440 free: (0x49B018), called by 0x610BC1EA
   65   60351 [main] selectleak 8440 peek_pipe: , already ready for read
   62   60413 [main] selectleak 8440 set_bits: me 0x49AF58, testing fd 0 ()
   62   60475 [main] selectleak 8440 set_bits: ready 1
   74   60549 [main] selectleak 8440 select_stuff::poll: returning 1
   61   60610 [main] selectleak 8440 select_stuff::cleanup: calling cleanup routines
   65   60675 [main] selectleak 8440 select_stuff::~select_stuff: deleting select records
   60   60735 [main] selectleak 8440 free: (0x49AF58), called by 0x610BC2A2
  108   60843 [main] selectleak 8440 calloc: (1, 44) = 49AF58, called by 61002389
   64   60907 [main] selectleak 8440 calloc: (1, 12) = 49B018, called by 61002389
  126   61033 [main] selectleak 8440 peek_pipe: , ready for read: avail 130892
   62   61095 [main] selectleak 8440 fhandler_base::ready_for_read: read_ready 1, avail 1
   62   61157 [main] selectleak 8440 select_stuff::cleanup: calling cleanup routines
   61   61218 [main] selectleak 8440 select_stuff::cleanup: calling cleanup routines
   62   61280 [main] selectleak 8440 select_stuff::~select_stuff: deleting select records
   61   61341 [main] selectleak 8440 free: (0x49AF58), called by 0x610BC2A2
  226   61567 [main] selectleak 8440 cygwin_select: 1, 0x23CCFC, 0x0, 0x0, 0x0

Notice how the "calloc: (1, 12) = 49B018" is only freed once between the two
"cygwin_select: 1, 0x23CCFC, ..."-lines.

$ cygcheck -c cygwin gcc4
Cygwin Package Information
Package              Version        Status
cygwin               1.7.9-1        OK
gcc4                 4.3.4-4        OK

Cheers,
Peter

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