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Re^3: Locked threads and tcp timeouts

by nikosv (Hermit)
on Feb 19, 2012 at 15:42 UTC ( #954876=note: print w/ replies, xml ) Need Help??


in reply to Re^2: Locked threads and tcp timeouts
in thread Locked threads and tcp timeouts

would a more drastic approach work ? like getting the underlying Win32 handle ($thr->_handle()) of the worker thread (since threads in Windows are created with CreateThread after all), and kill the thread by passing the handle to the TerminateThread api call ?

a note to the OP, when killing threads associated with calls to the dbms i.e sql execution, might lead to locked resources i.e tables or rows since there is no proper clean up


Comment on Re^3: Locked threads and tcp timeouts
Re^4: Locked threads and tcp timeouts
by BrowserUk (Pope) on Feb 20, 2012 at 02:50 UTC

    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.


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