i got it to work. i am the hack-master of the moment. check out test-pth-pthreads2.c.

Original commit message from CVS:
i got it to work. i am the hack-master of the moment. check out test-pth-pthreads2.c.

gst/cothreads/Makefile.am

@@ -8,11 +8,12 @@ noinst_LTLIBRARIES = libpth-mctx.la
 
 libpth_mctx_la_SOURCES = pth_mctx.c pth_p.h pth_vers.c pth.h pth_acdef.h pth_acmac.h
 
-noinst_PROGRAMS = test-pth test-pth-pthreads test-pthreads
+noinst_PROGRAMS = test-pth test-pth-pthreads test-pthreads test-pth-pthreads2
 
 test_pth_LDADD = libpth-mctx.la
 test_pth_pthreads_LDADD = libpth-mctx.la -lpthread
 test_pthreads_LDADD = -lpthread
+test_pth_pthreads2_LDADD = -lpthread libpth-mctx.la
 
 BUILT_SOURCES = pth_p.h
 

gst/cothreads/linuxthreads-internals.h

@@ -9,7 +9,7 @@
 #endif /* CURRENT_STACK_FRAME */
 
 #ifndef STACK_SIZE
-#define STACK_SIZE 0x20000 /* 2 M linuxthreads default stack size */
+#define STACK_SIZE 0x200000 /* 2 M linuxthreads default stack size */
 #endif
 
 typedef void * pthread_descr;

gst/cothreads/test-pth-pthreads2.c

@@ -0,0 +1,90 @@
+#define __USE_GNU /* non-posix functions */
+#include <pthread.h>
+#undef __USE_GNU
+#include <stdio.h>
+#include "linuxthreads-internals.h"
+#include "pth_p.h"
+
+/* this function is only really necessary to get the main thread's
+ * pthread_descr, as the other threads store the pthread_descr (actually the
+ * first member of struct _pthread_descr_struct, which points to itself for the
+ * default (non-indirected) case) at the top of the stack. */
+static _pthread_descr linuxthreads_self() 
+{
+  pthread_mutexattr_t mutexattr;
+  pthread_mutex_t mutex;
+  _pthread_descr self;
+  
+  pthread_mutexattr_init (&mutexattr);
+  pthread_mutexattr_setkind_np (&mutexattr, PTHREAD_MUTEX_ERRORCHECK_NP);
+  pthread_mutex_init (&mutex, &mutexattr);
+
+  pthread_mutex_lock (&mutex);
+  self = mutex.__m_owner;
+  pthread_mutex_unlock (&mutex);
+  
+  printf ("pthread_self: %d\n", pthread_self());
+  printf ("descr: %p\n", self);
+  printf ("*descr: %p\n", *(int*)self);
+  
+  return self;
+}
+
+pth_mctx_t main_context;
+int threadnum = 0;
+
+void cothread (void *unused)
+{
+  printf ("1.%d: current stack frame: %p\n", threadnum, CURRENT_STACK_FRAME);
+  printf ("1.%d: sleeping 2s...\n", threadnum);
+  sleep (2);
+  printf ("1.%d: returning to cothread 1.0\n");
+  pth_mctx_restore (&main_context);
+}
+
+void *pthread (void *unused) 
+{
+  char *sp = CURRENT_STACK_FRAME;
+  char *cothread_stack;
+  pth_mctx_t ctx;
+  _pthread_descr descr;
+  
+  descr = linuxthreads_self();
+  printf ("sp: %p\n", sp);
+  printf ("STACK_SIZE: %p\n", STACK_SIZE);
+  printf ("sp | STACK_SIZE: 0x%x\n", (int) sp | STACK_SIZE );
+  printf ("(sp | (STACK_SIZE-1))+1 - 1K: 0x%x\n", ((((int)sp | (STACK_SIZE-1))+1) - 1024));
+  printf ("*(sp | (STACK_SIZE-1))+1 - 1K: %p\n", *(int*)((((long int)sp | (STACK_SIZE-1))+1) - 1024));
+  
+  while (threadnum < 10) {
+    if (posix_memalign (&cothread_stack, STACK_SIZE, STACK_SIZE)) {
+      printf ("could not malloc a chunk of aligned memory\n");
+      exit (-1);
+    }
+    
+    printf ("1: setting *%p = %p\n", cothread_stack + STACK_SIZE - 1024, descr);
+    memcpy(cothread_stack + STACK_SIZE - 1024, descr, 1024);
+    
+    pth_mctx_save (&main_context);
+    printf ("1: spawning new thread, bottom = %p\n", cothread_stack);
+    pth_mctx_set (&ctx, cothread, cothread_stack, cothread_stack + STACK_SIZE - 1024);
+    printf ("1: switching to cothread %d...\n", ++threadnum);
+    pth_mctx_switch (&main_context, &ctx);
+  }
+  
+  printf ("1: back, returning...\n");
+  
+  return NULL;
+}
+
+int main (int argc, char *argv[]) 
+{
+  pthread_t tid;
+  
+  pthread_create (&tid, NULL, pthread, NULL);
+  pthread_join (tid, NULL);
+  
+  linuxthreads_self();
+  
+  exit (0);
+}

gst/cothreads/test-pthreads.c

@@ -2,6 +2,7 @@
 #include <pthread.h>
 #undef __USE_GNU
 #include <stdio.h>
+#include "linuxthreads-internals.h"
 
 // the thread_self algorithm:
 /*
@@ -19,6 +20,10 @@
 #endif
 */
 
+/* this function is only really necessary to get the main thread's
+ * pthread_descr, as the other threads store the pthread_descr (actually the
+ * first member of struct _pthread_descr_struct, which points to itself for the
+ * default (non-indirected) case) at the top of the stack. */
 static _pthread_descr linuxthreads_self() 
 {
   pthread_mutexattr_t mutexattr;
@@ -35,22 +40,33 @@ static _pthread_descr linuxthreads_self()
   
   printf ("pthread_self: %d\n", pthread_self());
   printf ("descr: %p\n", self);
+  printf ("*descr: %p\n", *(int*)self);
   
   return self;
 }
 
 void *pthread (void *unused) 
 {
+  char *sp = CURRENT_STACK_FRAME;
+  
   linuxthreads_self();
+  printf ("sp: %p\n", sp);
+  printf ("sp | 0x020000: 0x%x\n", (int) sp | 0x020000 );
+  printf ("(sp | (0x020000-1))+1 - 1K: 0x%x\n", ((((int)sp | (STACK_SIZE-1))+1) - 1024));
+  printf ("*(sp | (0x020000-1))+1 - 1K: %p\n", *(int*)((((long int)sp | (STACK_SIZE-1))+1) - 1024));
+  printf ("(sp &~ (0x020000-1))+1: 0x%x\n", (((int)sp &~ (STACK_SIZE-1))+1));
   return NULL;
 }
 
 int main (int argc, char *argv[]) 
 {
   pthread_t tid;
+  int i;
   
-  pthread_create (&tid, NULL, pthread, NULL);
-  pthread_join (tid, NULL);
+  for (i=0; i<10; i++) {
+    pthread_create (&tid, NULL, pthread, NULL);
+    sleep(2);
+  }
   
   linuxthreads_self();
   exit (0);