Rework threads destruct call

[p5sagit/p5-mst-13.2.git] / ext / threads / threads.xs

#define PERL_NO_GET_CONTEXT
#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#ifdef HAS_PPPORT_H
#  define NEED_newRV_noinc
#  define NEED_sv_2pv_nolen
#  include "ppport.h"
#  include "threads.h"
#endif

#ifdef USE_ITHREADS


#ifdef WIN32
#include <windows.h>
#include <win32thread.h>
#else
#ifdef OS2
typedef perl_os_thread pthread_t;
#else
#include <pthread.h>
#endif
#include <thread.h>
#define PERL_THREAD_SETSPECIFIC(k,v) pthread_setspecific(k,v)
#ifdef OLD_PTHREADS_API
#define PERL_THREAD_DETACH(t) pthread_detach(&(t))
#else
#define PERL_THREAD_DETACH(t) pthread_detach((t))
#endif  /* OLD_PTHREADS_API */
#endif




/* Values for 'state' member */
#define PERL_ITHR_JOINABLE		0
#define PERL_ITHR_DETACHED		1
#define PERL_ITHR_FINISHED		4
#define PERL_ITHR_JOINED		2

typedef struct ithread_s {
    struct ithread_s *next;	/* Next thread in the list */
    struct ithread_s *prev;	/* Prev thread in the list */
    PerlInterpreter *interp;	/* The threads interpreter */
    UV tid;              	/* Threads module's thread id */
    perl_mutex mutex; 		/* Mutex for updating things in this struct */
    IV count;			/* How many SVs have a reference to us */
    signed char state;		/* Are we detached ? */
    int gimme;			/* Context of create */
    SV* init_function;          /* Code to run */
    SV* params;                 /* Args to pass function */
#ifdef WIN32
	DWORD	thr;            /* OS's idea if thread id */
	HANDLE handle;          /* OS's waitable handle */
#else
  	pthread_t thr;          /* OS's handle for the thread */
#endif
} ithread;

#define MY_CXT_KEY "threads::_guts" XS_VERSION

typedef struct {
    ithread *thread;
} my_cxt_t;

START_MY_CXT


static ithread *threads;

static perl_mutex create_destruct_mutex;  /* protects the creation and destruction of threads*/

static UV tid_counter = 0;
static IV active_threads = 0;


static void
S_ithread_set (pTHX_ ithread* thread)
{
    dMY_CXT;
    MY_CXT.thread = thread;
}

static ithread*
S_ithread_get (pTHX) {
    dMY_CXT;
    return MY_CXT.thread;
}


/* free any data (such as the perl interpreter) attached to an
 * ithread structure. This is a bit like undef on SVs, where the SV
 * isn't freed, but the PVX is.
 * Must be called with thread->mutex already held
 */

static void
S_ithread_clear(pTHX_ ithread* thread)
{
    PerlInterpreter *interp;
    assert(thread->state & PERL_ITHR_FINISHED &&
    	    (thread->state & PERL_ITHR_DETACHED ||
	    thread->state & PERL_ITHR_JOINED));

    interp = thread->interp;
    if (interp) {
	dTHXa(interp);
	ithread* current_thread;
#ifdef OEMVS
	void *ptr;
#endif
	PERL_SET_CONTEXT(interp);
	current_thread = S_ithread_get(aTHX);
	S_ithread_set(aTHX_ thread);
	
	SvREFCNT_dec(thread->params);

	thread->params = Nullsv;
	perl_destruct(interp);
	thread->interp = NULL;
    }
    if (interp)
	perl_free(interp);
    PERL_SET_CONTEXT(aTHX);
}


/*
 *  free an ithread structure and any attached data if its count == 0
 */
static void
S_ithread_destruct (pTHX_ ithread* thread)
{
#ifdef WIN32
        HANDLE handle;
#endif

	MUTEX_LOCK(&thread->mutex);

        /* Thread is still in use */
	if (thread->count != 0) {
		MUTEX_UNLOCK(&thread->mutex);
		return;
	}

	/* Remove from circular list of threads */
	MUTEX_LOCK(&create_destruct_mutex);
	thread->next->prev = thread->prev;
	thread->prev->next = thread->next;
	thread->next = NULL;
	thread->prev = NULL;
	MUTEX_UNLOCK(&create_destruct_mutex);

	/* Thread is now disowned */
	S_ithread_clear(aTHX_ thread);

#ifdef WIN32
        handle = thread->handle;
        thread->handle = NULL;
#endif
	MUTEX_UNLOCK(&thread->mutex);
	MUTEX_DESTROY(&thread->mutex);

#ifdef WIN32
        if (handle)
            CloseHandle(handle);
#endif

        /* Call PerlMemShared_free() in the context of the "first" interpreter
         * per http://www.nntp.perl.org/group/perl.perl5.porters/110772
         */
        aTHX = PL_curinterp;
        PerlMemShared_free(thread);
}

int
Perl_ithread_hook(pTHX)
{
    int veto_cleanup = 0;
    MUTEX_LOCK(&create_destruct_mutex);
    if (aTHX == PL_curinterp && active_threads != 1) {
	if (ckWARN_d(WARN_THREADS))
	    Perl_warn(aTHX_ "A thread exited while %" IVdf " threads were running",
						      active_threads);
	veto_cleanup = 1;
    }
    MUTEX_UNLOCK(&create_destruct_mutex);
    return veto_cleanup;
}

static void
S_ithread_detach(pTHX_ ithread *thread)
{
    MUTEX_LOCK(&thread->mutex);
    if (!(thread->state & (PERL_ITHR_DETACHED|PERL_ITHR_JOINED))) {
	thread->state |= PERL_ITHR_DETACHED;
#ifdef WIN32
	CloseHandle(thread->handle);
	thread->handle = 0;
#else
	PERL_THREAD_DETACH(thread->thr);
#endif
    }
    if ((thread->state & PERL_ITHR_FINISHED) &&
        (thread->state & PERL_ITHR_DETACHED)) {
	MUTEX_UNLOCK(&thread->mutex);
	S_ithread_destruct(aTHX_ thread);
    }
    else {
	MUTEX_UNLOCK(&thread->mutex);
    }
}

/* MAGIC (in mg.h sense) hooks */

int
ithread_mg_get(pTHX_ SV *sv, MAGIC *mg)
{
    ithread *thread = (ithread *) mg->mg_ptr;
    SvIV_set(sv, PTR2IV(thread));
    SvIOK_on(sv);
    return 0;
}

int
ithread_mg_free(pTHX_ SV *sv, MAGIC *mg)
{
    ithread *thread = (ithread *) mg->mg_ptr;
    MUTEX_LOCK(&thread->mutex);
    thread->count--;
    if (thread->count == 0) {
       if(thread->state & PERL_ITHR_FINISHED &&
          (thread->state & PERL_ITHR_DETACHED ||
           thread->state & PERL_ITHR_JOINED))
       {
            MUTEX_UNLOCK(&thread->mutex);
            S_ithread_destruct(aTHX_ thread);
       }
       else {
	    MUTEX_UNLOCK(&thread->mutex);
       }    
    }
    else {
	MUTEX_UNLOCK(&thread->mutex);
    }
    return 0;
}

int
ithread_mg_dup(pTHX_ MAGIC *mg, CLONE_PARAMS *param)
{
    ithread *thread = (ithread *) mg->mg_ptr;
    MUTEX_LOCK(&thread->mutex);
    thread->count++;
    MUTEX_UNLOCK(&thread->mutex);
    return 0;
}

MGVTBL ithread_vtbl = {
 ithread_mg_get,	/* get */
 0,			/* set */
 0,			/* len */
 0,			/* clear */
 ithread_mg_free,	/* free */
 0,			/* copy */
 ithread_mg_dup		/* dup */
};


/*
 *	Starts executing the thread. Needs to clean up memory a tad better.
 *      Passed as the C level function to run in the new thread
 */

#ifdef WIN32
static THREAD_RET_TYPE
S_ithread_run(LPVOID arg) {
#else
static void*
S_ithread_run(void * arg) {
#endif
	ithread* thread = (ithread*) arg;
	dTHXa(thread->interp);
	PERL_SET_CONTEXT(thread->interp);
	S_ithread_set(aTHX_ thread);

#if 0
	/* Far from clear messing with ->thr child-side is a good idea */
	MUTEX_LOCK(&thread->mutex);
#ifdef WIN32
	thread->thr = GetCurrentThreadId();
#else
	thread->thr = pthread_self();
#endif
 	MUTEX_UNLOCK(&thread->mutex);
#endif

	PL_perl_destruct_level = 2;

	{
		AV* params = (AV*) SvRV(thread->params);
		int len = (int)av_len(params)+1;
		int ii;
		dSP;
		ENTER;
		SAVETMPS;
		PUSHMARK(SP);
		for(ii = 0; ii < len; ii++) {
		    XPUSHs(av_shift(params));
		}
		PUTBACK;
		len = (int)call_sv(thread->init_function, thread->gimme|G_EVAL);

		SPAGAIN;
		for (ii=len-1; ii >= 0; ii--) {
		  SV *sv = POPs;
		  av_store(params, ii, SvREFCNT_inc(sv));
		}
		if (SvTRUE(ERRSV) && ckWARN_d(WARN_THREADS)) {
		    Perl_warn(aTHX_ "thread failed to start: %" SVf, ERRSV);
		}
		FREETMPS;
		LEAVE;
		SvREFCNT_dec(thread->init_function);
	}

	PerlIO_flush((PerlIO*)NULL);
	MUTEX_LOCK(&thread->mutex);
	thread->state |= PERL_ITHR_FINISHED;

	if (thread->state & PERL_ITHR_DETACHED) {
		MUTEX_UNLOCK(&thread->mutex);
		S_ithread_destruct(aTHX_ thread);
	} else {
		MUTEX_UNLOCK(&thread->mutex);
	}
	MUTEX_LOCK(&create_destruct_mutex);
	active_threads--;
	assert( active_threads >= 0 );
	MUTEX_UNLOCK(&create_destruct_mutex);

#ifdef WIN32
	return (DWORD)0;
#else
	return 0;
#endif
}

static SV *
ithread_to_SV(pTHX_ SV *obj, ithread *thread, char *classname, bool inc)
{
    SV *sv;
    MAGIC *mg;
    if (inc) {
	MUTEX_LOCK(&thread->mutex);
	thread->count++;
	MUTEX_UNLOCK(&thread->mutex);
    }
    if (!obj)
     obj = newSV(0);
    sv = newSVrv(obj,classname);
    sv_setiv(sv,PTR2IV(thread));
    mg = sv_magicext(sv,Nullsv,PERL_MAGIC_shared_scalar,&ithread_vtbl,(char *)thread,0);
    mg->mg_flags |= MGf_DUP;
    SvREADONLY_on(sv);
    return obj;
}

static ithread *
SV_to_ithread(pTHX_ SV *sv)
{
    if (SvROK(sv))
     {
      return INT2PTR(ithread*, SvIV(SvRV(sv)));
     }
    else
     {
      return S_ithread_get(aTHX);
     }
}

/*
 * ithread->create(); ( aka ithread->new() )
 * Called in context of parent thread
 */

static SV *
S_ithread_create(pTHX_ SV *obj, char* classname, SV* init_function, SV* params)
{
	ithread*	thread;
	CLONE_PARAMS	clone_param;
	ithread*        current_thread = S_ithread_get(aTHX);

	SV**            tmps_tmp = PL_tmps_stack;
	IV              tmps_ix  = PL_tmps_ix;
#ifndef WIN32
	int		failure;
	const char*	panic = NULL;
#endif


	MUTEX_LOCK(&create_destruct_mutex);
	thread = (ithread *) PerlMemShared_malloc(sizeof(ithread));
	if (!thread) {	
	    MUTEX_UNLOCK(&create_destruct_mutex);
	    PerlLIO_write(PerlIO_fileno(Perl_error_log),
			  PL_no_mem, strlen(PL_no_mem));
	    my_exit(1);
	}
	Zero(thread,1,ithread);

        /* Add to threads list */
	thread->next = threads;
	thread->prev = threads->prev;
	threads->prev = thread;
	thread->prev->next = thread;

	/* Set count to 1 immediately in case thread exits before
	 * we return to caller !
	 */
	thread->count = 1;
	MUTEX_INIT(&thread->mutex);
	thread->tid = tid_counter++;
	thread->gimme = GIMME_V;

	/* "Clone" our interpreter into the thread's interpreter
	 * This gives thread access to "static data" and code.
	 */

	PerlIO_flush((PerlIO*)NULL);
	S_ithread_set(aTHX_ thread);

	SAVEBOOL(PL_srand_called); /* Save this so it becomes the correct
	                              value */
	PL_srand_called = FALSE; /* Set it to false so we can detect
	                            if it gets set during the clone */

#ifdef WIN32
	thread->interp = perl_clone(aTHX, CLONEf_KEEP_PTR_TABLE | CLONEf_CLONE_HOST);
#else
	thread->interp = perl_clone(aTHX, CLONEf_KEEP_PTR_TABLE);
#endif
	/* perl_clone leaves us in new interpreter's context.
	   As it is tricky to spot an implicit aTHX, create a new scope
	   with aTHX matching the context for the duration of
	   our work for new interpreter.
	 */
	{
	    dTHXa(thread->interp);

	    MY_CXT_CLONE;

            /* Here we remove END blocks since they should only run
	       in the thread they are created
            */
            SvREFCNT_dec(PL_endav);
            PL_endav = newAV();
            clone_param.flags = 0;
	    thread->init_function = sv_dup(init_function, &clone_param);
	    if (SvREFCNT(thread->init_function) == 0) {
		SvREFCNT_inc(thread->init_function);
	    }
	    


	    thread->params = sv_dup(params, &clone_param);
	    SvREFCNT_inc(thread->params);


	    /* The code below checks that anything living on
	       the tmps stack and has been cloned (so it lives in the
	       ptr_table) has a refcount higher than 0

	       If the refcount is 0 it means that a something on the
	       stack/context was holding a reference to it and
	       since we init_stacks() in perl_clone that won't get
	       cleaned and we will get a leaked scalar.
	       The reason it was cloned was that it lived on the
	       @_ stack.

	       Example of this can be found in bugreport 15837
	       where calls in the parameter list end up as a temp

	       One could argue that this fix should be in perl_clone
	    */
	       

	    while (tmps_ix > 0) { 
	      SV* sv = (SV*)ptr_table_fetch(PL_ptr_table, tmps_tmp[tmps_ix]);
	      tmps_ix--;
	      if (sv && SvREFCNT(sv) == 0) {
		SvREFCNT_inc(sv);
		SvREFCNT_dec(sv);
	      }
	    }
	    


	    SvTEMP_off(thread->init_function);
	    ptr_table_free(PL_ptr_table);
	    PL_ptr_table = NULL;
	    PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
	}
	S_ithread_set(aTHX_ current_thread);
	PERL_SET_CONTEXT(aTHX);

	/* Start the thread */

#ifdef WIN32
	thread->handle = CreateThread(NULL, 0, S_ithread_run,
			(LPVOID)thread, 0, &thread->thr);
#else
	{
	  static pthread_attr_t attr;
	  static int attr_inited = 0;
	  static int attr_joinable = PTHREAD_CREATE_JOINABLE;
	  if (!attr_inited) {
	    attr_inited = 1;
	    pthread_attr_init(&attr);
	  }
#  ifdef PTHREAD_ATTR_SETDETACHSTATE
            PTHREAD_ATTR_SETDETACHSTATE(&attr, attr_joinable);
#  endif
#  ifdef THREAD_CREATE_NEEDS_STACK
	    if(pthread_attr_setstacksize(&attr, THREAD_CREATE_NEEDS_STACK))
	      panic = "panic: pthread_attr_setstacksize failed";
#  endif

#ifdef OLD_PTHREADS_API
	    failure
	      = panic ? 1 : pthread_create( &thread->thr, attr,
					    S_ithread_run, (void *)thread);
#else
#  if defined(HAS_PTHREAD_ATTR_SETSCOPE) && defined(PTHREAD_SCOPE_SYSTEM)
	  pthread_attr_setscope( &attr, PTHREAD_SCOPE_SYSTEM );
#  endif
	  failure
	    = panic ? 1 : pthread_create( &thread->thr, &attr,
					  S_ithread_run, (void *)thread);
#endif
	}
#endif

	if (
#ifdef WIN32
	    thread->handle == NULL
#else
	    failure
#endif
	    ) {
	  MUTEX_UNLOCK(&create_destruct_mutex);
	  sv_2mortal(params);
	  S_ithread_destruct(aTHX_ thread);
#ifndef WIN32
	  if (panic)
	    Perl_croak(aTHX_ panic);
#endif
	  return &PL_sv_undef;
	}
	active_threads++;
	MUTEX_UNLOCK(&create_destruct_mutex);
	sv_2mortal(params);

	return ithread_to_SV(aTHX_ obj, thread, classname, FALSE);
}

static SV*
S_ithread_self (pTHX_ SV *obj, char* Class)
{
   ithread *thread = S_ithread_get(aTHX);
   if (thread)
	return ithread_to_SV(aTHX_ obj, thread, Class, TRUE);
   else
	Perl_croak(aTHX_ "panic: cannot find thread data");
   return NULL; /* silence compiler warning */
}


/* Joins the thread.
 * This code takes the return value from the call_sv and sends it back.
 */
static AV*
S_ithread_join(pTHX_ SV *obj)
{
    ithread *thread = SV_to_ithread(aTHX_ obj);
    MUTEX_LOCK(&thread->mutex);
    if (thread->state & PERL_ITHR_DETACHED) {
	MUTEX_UNLOCK(&thread->mutex);
	Perl_croak(aTHX_ "Cannot join a detached thread");
    }
    else if (thread->state & PERL_ITHR_JOINED) {
	MUTEX_UNLOCK(&thread->mutex);
	Perl_croak(aTHX_ "Thread already joined");
    }
    else {
        AV* retparam;
#ifdef WIN32
	DWORD waitcode;
#else
	void *retval;
#endif
	MUTEX_UNLOCK(&thread->mutex);
#ifdef WIN32
	waitcode = WaitForSingleObject(thread->handle, INFINITE);
	CloseHandle(thread->handle);
	thread->handle = 0;
#else
	pthread_join(thread->thr,&retval);
#endif
	MUTEX_LOCK(&thread->mutex);
	
	/* sv_dup over the args */
	{
	  ithread*        current_thread;
	  AV* params = (AV*) SvRV(thread->params);	
	  PerlInterpreter *other_perl = thread->interp;
	  CLONE_PARAMS clone_params;
	  clone_params.stashes = newAV();
	  clone_params.flags = CLONEf_JOIN_IN;
	  PL_ptr_table = ptr_table_new();
	  current_thread = S_ithread_get(aTHX);
	  S_ithread_set(aTHX_ thread);
	  /* ensure 'meaningful' addresses retain their meaning */
	  ptr_table_store(PL_ptr_table, &other_perl->Isv_undef, &PL_sv_undef);
	  ptr_table_store(PL_ptr_table, &other_perl->Isv_no, &PL_sv_no);
	  ptr_table_store(PL_ptr_table, &other_perl->Isv_yes, &PL_sv_yes);

#if 0
	  {
	    I32 len = av_len(params)+1;
	    I32 i;
	    for(i = 0; i < len; i++) {
	      sv_dump(SvRV(AvARRAY(params)[i]));
	    }
	  }
#endif
	  retparam = (AV*) sv_dup((SV*)params, &clone_params);
#if 0
	  {
	    I32 len = av_len(retparam)+1;
	    I32 i;
	    for(i = 0; i < len; i++) {
		sv_dump(SvRV(AvARRAY(retparam)[i]));
	    }
	  }
#endif
	  S_ithread_set(aTHX_ current_thread);
	  SvREFCNT_dec(clone_params.stashes);
	  SvREFCNT_inc(retparam);
	  ptr_table_free(PL_ptr_table);
	  PL_ptr_table = NULL;

	}
	/* We are finished with it */
	thread->state |= PERL_ITHR_JOINED;
	S_ithread_clear(aTHX_ thread);
	MUTEX_UNLOCK(&thread->mutex);
    	
	return retparam;
    }
    return (AV*)NULL;
}

static void
S_ithread_DESTROY(pTHX_ SV *sv)
{
    ithread *thread = SV_to_ithread(aTHX_ sv);
    sv_unmagic(SvRV(sv),PERL_MAGIC_shared_scalar);
}

#endif /* USE_ITHREADS */

MODULE = threads		PACKAGE = threads	PREFIX = ithread_
PROTOTYPES: DISABLE

#ifdef USE_ITHREADS

void
ithread_create(...)
    PREINIT:
        char *classname;
        SV *function_to_call;
        AV *params;
        int ii;
    CODE:
        if (items < 2)
            Perl_croak(aTHX_ "Usage: threads->create(function, ...)");

        classname = (char *)SvPV_nolen(ST(0));
        function_to_call = ST(1);

        /* Function args */
        params = newAV();
        if (items > 2) {
            for (ii=2; ii < items; ii++) {
                av_push(params, SvREFCNT_inc(ST(ii)));
            }
        }

        /* Create thread */
        ST(0) = sv_2mortal(S_ithread_create(aTHX_ Nullsv,
                                               classname,
                                               function_to_call,
                                               newRV_noinc((SV*)params)));
        /* XSRETURN(1); - implied */


void
ithread_list(...)
    PREINIT:
        char *classname;
        ithread *thr;
        int list_context;
        IV count = 0;
    PPCODE:
        /* Class method only */
        if (SvROK(ST(0)))
            Perl_croak(aTHX_ "Usage: threads->list()");
        classname = (char *)SvPV_nolen(ST(0));

        /* Calling context */
        list_context = (GIMME_V == G_ARRAY);

        /* Walk through threads list */
        MUTEX_LOCK(&create_destruct_mutex);
        for (thr = threads->next;
             thr != threads;
             thr = thr->next)
        {
            /* Ignore detached or joined threads */
            if (thr->state & (PERL_ITHR_DETACHED|PERL_ITHR_JOINED)) {
                continue;
            }
            /* Push object on stack if list context */
            if (list_context) {
                XPUSHs(sv_2mortal(ithread_to_SV(aTHX_ NULL, thr, classname, TRUE)));
            }
            count++;
        }
        MUTEX_UNLOCK(&create_destruct_mutex);
        /* If scalar context, send back count */
        if (! list_context) {
            XSRETURN_IV(count);
        }


void
ithread_self(...)
    PREINIT:
        char *classname;
    CODE:
        /* Class method only */
        if (SvROK(ST(0)))
            Perl_croak(aTHX_ "Usage: threads->self()");
        classname = (char *)SvPV_nolen(ST(0));

        ST(0) = sv_2mortal(S_ithread_self(aTHX_ Nullsv, classname));
        /* XSRETURN(1); - implied */


void
ithread_tid(...)
    PREINIT:
        ithread *thread;
    CODE:
        thread = SV_to_ithread(aTHX_ ST(0));
        XST_mUV(0, thread->tid);
        /* XSRETURN(1); - implied */


void
ithread_join(...)
    PREINIT:
        AV *params;
        int len;
        int ii;
    PPCODE:
        /* Object method only */
        if (! sv_isobject(ST(0)))
            Perl_croak(aTHX_ "Usage: $thr->join()");

        /* Join thread and get return values */
        params = S_ithread_join(aTHX_ ST(0));
        if (! params) {
            XSRETURN_UNDEF;
        }

        /* Put return values on stack */
        len = (int)AvFILL(params);
        for (ii=0; ii <= len; ii++) {
            SV* param = av_shift(params);
            XPUSHs(sv_2mortal(param));
        }

        /* Free return value array */
        SvREFCNT_dec(params);


void
ithread_yield(...)
    CODE:
        YIELD;


void
ithread_detach(...)
    PREINIT:
        ithread *thread;
    CODE:
        thread = SV_to_ithread(aTHX_ ST(0));
        S_ithread_detach(aTHX_ thread);


void
ithread_DESTROY(...)
    CODE:
        S_ithread_DESTROY(aTHX_ ST(0));


void
ithread_equal(...)
    CODE:
        /* Compares TIDs to determine thread equality.
         * Return 0 on false for backward compatibility.
         */
        if (sv_isobject(ST(0)) && sv_isobject(ST(1))) {
            ithread *thr1 = INT2PTR(ithread *, SvIV(SvRV(ST(0))));
            ithread *thr2 = INT2PTR(ithread *, SvIV(SvRV(ST(1))));
            if (thr1->tid == thr2->tid) {
                XST_mYES(0);
            } else {
                XST_mIV(0, 0);
            }
        } else {
            XST_mIV(0, 0);
        }
        /* XSRETURN(1); - implied */


void
ithread_object(...)
    PREINIT:
        char *classname;
        UV tid;
        ithread *thr;
        int found = 0;
    CODE:
        /* Class method only */
        if (SvROK(ST(0)))
            Perl_croak(aTHX_ "Usage: threads->object($tid)");
        classname = (char *)SvPV_nolen(ST(0));

        if ((items < 2) || ! SvOK(ST(1))) {
            XSRETURN_UNDEF;
        }

        tid = SvUV(ST(1));

        /* Walk through threads list */
        MUTEX_LOCK(&create_destruct_mutex);
        for (thr = threads->next;
             thr != threads;
             thr = thr->next)
        {
            /* Look for TID, but ignore detached or joined threads */
            if ((thr->tid != tid) ||
                (thr->state & (PERL_ITHR_DETACHED|PERL_ITHR_JOINED)))
            {
                continue;
            }
            /* Put object on stack */
            ST(0) = sv_2mortal(ithread_to_SV(aTHX_ NULL, thr, classname, TRUE));
            found = 1;
            break;
        }
        MUTEX_UNLOCK(&create_destruct_mutex);
        if (! found) {
            XSRETURN_UNDEF;
        }
        /* XSRETURN(1); - implied */


void
ithread__handle(...);
    PREINIT:
        ithread *thread;
    CODE:
        thread = SV_to_ithread(aTHX_ ST(0));
#ifdef WIN32
        XST_mUV(0, PTR2UV(thread->handle));
#else
        XST_mUV(0, PTR2UV(&thread->thr));
#endif
        /* XSRETURN(1); - implied */

#endif /* USE_ITHREADS */

BOOT:
{
#ifdef USE_ITHREADS
        MY_CXT_INIT;
	ithread* thread;
	PL_perl_destruct_level = 2;
	MUTEX_INIT(&create_destruct_mutex);
	MUTEX_LOCK(&create_destruct_mutex);
	PL_threadhook = &Perl_ithread_hook;
	thread  = (ithread *) PerlMemShared_malloc(sizeof(ithread));
	if (!thread) {
	    PerlLIO_write(PerlIO_fileno(Perl_error_log),
			  PL_no_mem, strlen(PL_no_mem));
	    my_exit(1);
	}
	Zero(thread,1,ithread);
	PL_perl_destruct_level = 2;
	MUTEX_INIT(&thread->mutex);

        /* Head of the threads list */
	threads = thread;
	thread->next = thread;
        thread->prev = thread;

	thread->interp = aTHX;
	thread->count  = 1;  /* Immortal. */
	thread->tid = tid_counter++;
	active_threads++;
	thread->state = PERL_ITHR_DETACHED;
#ifdef WIN32
	thread->thr = GetCurrentThreadId();
#else
	thread->thr = pthread_self();
#endif

	S_ithread_set(aTHX_ thread);
	MUTEX_UNLOCK(&create_destruct_mutex);
#endif /* USE_ITHREADS */
}