Re^4: Locked threads and tcp timeouts

[BrowserUk]

There are two problems with the idea.

1. I've never managed to work out how to use the value returned from _handle().

   It appears to be returned in the IV slot of the SV:

   SV = IV(0x3afb470) at 0x3afb478
     REFCNT = 1
     FLAGS = (PADMY,IOK,pIOK)
     IV = 94514760
   

   but all my attempts to use it from XS in calls to the OS result in The handle is invalid.

2. Terminating threads is a desperate measure as it does not allow either the thread itself, the OS, or Perl to clean up after themselves, leading to a massive memory leak. Not to mention the potential for all sorts of nasties with dangling pointers etc.

   If you bypass the first problem by calling an XS sub that gets the current thread handle from the OS -- which isn't very useful as it can only be called from within the thread to be killed -- and run a loop that creates threads and has them self terminate, then you see the scope of the massive memory leak it creates:

   #! perl -slw
   use strict;
   use Inline C => Config => BUILD_NOISY => 1;
   use Inline C => <<'END_C',  NAME => 'TerminateThreadTest', CLEAN_AFTER
   +_BUILD => 0;
   
   int killThread( SV *t, SV *ec ) {
       printf( "t:%p ec:%d\n", SvIV( t ), SvIV( ec ) );
       return TerminateThread( SvIV( t ), SvIV( ec ) );
   }
   
   void hariKari( SV *exitCode ) {
       TerminateThread( GetCurrentThread(), SvIV( exitCode ) );
   }
   
   END_C
   use Devel::Peek;
   use threads;
   
   for( 1 .. 100 ) {
       my $t = async {
           sleep 5;
           hariKari( 12345 );
       };
       sleep 10;
   }
   

On my system, the above script leaks around 2MB for every thread killed. Whilst that could be reduce by spawning early and trimming the stack etc., it will never be zero.