0.9.2.42:
[sbcl.git] / src / runtime / thread.c
index 759a1c6..4d49ae3 100644 (file)
@@ -10,7 +10,8 @@
 
 #include "sbcl.h"
 #include "runtime.h"
-#include "validate.h"          /* for CONTROL_STACK_SIZE etc */
+#include "validate.h"           /* for CONTROL_STACK_SIZE etc */
+#include "alloc.h"
 #include "thread.h"
 #include "arch.h"
 #include "target-arch-os.h"
 
 #define ALIEN_STACK_SIZE (1*1024*1024) /* 1Mb size chosen at random */
 
-int dynamic_values_bytes=4096*sizeof(lispobj); /* same for all threads */
+int dynamic_values_bytes=4096*sizeof(lispobj);  /* same for all threads */
 struct thread *all_threads;
 volatile lispobj all_threads_lock;
-volatile lispobj thread_start_lock;
 extern struct interrupt_data * global_interrupt_data;
 extern int linux_no_threads_p;
 
+#ifdef LISP_FEATURE_SB_THREAD
+/* When trying to get all_threads_lock one should make sure that
+ * sig_stop_for_gc is not blocked. Else there would be a possible
+ * deadlock: gc locks it, other thread blocks signals, gc sends stop
+ * request to other thread and waits, other thread blocks on lock. */
+void check_sig_stop_for_gc_can_arrive_or_lose()
+{
+    /* Get the current sigmask, by blocking the empty set. */
+    sigset_t empty,current;
+    sigemptyset(&empty);
+    thread_sigmask(SIG_BLOCK, &empty, &current);
+    if (sigismember(&current,SIG_STOP_FOR_GC))
+        lose("SIG_STOP_FOR_GC is blocked\n");
+    if (SymbolValue(INTERRUPTS_ENABLED,arch_os_get_current_thread()) == NIL)
+        lose("interrupts disabled\n");
+    if (arch_pseudo_atomic_atomic(NULL))
+        lose("n pseudo atomic\n");
+}
+
+#ifdef QSHOW_SIGNALS
+#define FSHOW_SIGNAL FSHOW
+#else
+#define FSHOW_SIGNAL(args)
+#endif
+
+#define GET_ALL_THREADS_LOCK(name) \
+    { \
+        sigset_t _newset,_oldset; \
+        sigemptyset(&_newset); \
+        sigaddset_blockable(&_newset); \
+        sigdelset(&_newset,SIG_STOP_FOR_GC); \
+        thread_sigmask(SIG_BLOCK, &_newset, &_oldset); \
+        check_sig_stop_for_gc_can_arrive_or_lose(); \
+        FSHOW_SIGNAL((stderr,"/%s:waiting on lock=%ld, thread=%ld\n",name, \
+               all_threads_lock,arch_os_get_current_thread()->os_thread)); \
+        get_spinlock(&all_threads_lock,(long)arch_os_get_current_thread()); \
+        FSHOW_SIGNAL((stderr,"/%s:got lock, thread=%ld\n", \
+               name,arch_os_get_current_thread()->os_thread));
+
+#define RELEASE_ALL_THREADS_LOCK(name) \
+        FSHOW_SIGNAL((stderr,"/%s:released lock\n",name)); \
+        release_spinlock(&all_threads_lock); \
+        thread_sigmask(SIG_SETMASK,&_oldset,0); \
+    }
+#endif
+
 int
 initial_thread_trampoline(struct thread *th)
 {
@@ -43,7 +89,7 @@ initial_thread_trampoline(struct thread *th)
     th->unbound_marker = UNBOUND_MARKER_WIDETAG;
     if(arch_os_thread_init(th)==0) return 1;
 
-    if(th->pid < 1) lose("th->pid not set up right");
+    if(th->os_thread < 1) lose("th->os_thread not set up right");
     th->state=STATE_RUNNING;
 #if defined(LISP_FEATURE_X86) || defined(LISP_FEATURE_X86_64)
     return call_into_lisp_first_time(function,args,0);
@@ -52,23 +98,23 @@ initial_thread_trampoline(struct thread *th)
 #endif
 }
 
-/* this is the first thing that clone() runs in the child (which is
- * why the silly calling convention).  Basically it calls the user's
- * requested lisp function after doing arch_os_thread_init and
- * whatever other bookkeeping needs to be done
- */
-
 #ifdef LISP_FEATURE_SB_THREAD
+
+/* this is the first thing that runs in the child (which is why the
+ * silly calling convention).  Basically it calls the user's requested
+ * lisp function after doing arch_os_thread_init and whatever other
+ * bookkeeping needs to be done
+ */
 int
 new_thread_trampoline(struct thread *th)
 {
     lispobj function;
     function = th->unbound_marker;
     th->unbound_marker = UNBOUND_MARKER_WIDETAG;
-    if(arch_os_thread_init(th)==0) return 1;   
+    if(arch_os_thread_init(th)==0) return 1;
 
     /* wait here until our thread is linked into all_threads: see below */
-    while(th->pid<1) sched_yield();
+    while(th->os_thread<1) sched_yield();
 
     th->state=STATE_RUNNING;
     return funcall0(function);
@@ -76,58 +122,58 @@ new_thread_trampoline(struct thread *th)
 #endif /* LISP_FEATURE_SB_THREAD */
 
 /* this is called from any other thread to create the new one, and
- * initialize all parts of it that can be initialized from another 
- * thread 
+ * initialize all parts of it that can be initialized from another
+ * thread
  */
 
 struct thread * create_thread_struct(lispobj initial_function) {
     union per_thread_data *per_thread;
-    struct thread *th=0;       /*  subdue gcc */
+    struct thread *th=0;        /*  subdue gcc */
     void *spaces=0;
 
     /* may as well allocate all the spaces at once: it saves us from
      * having to decide what to do if only some of the allocations
      * succeed */
     spaces=os_validate(0,
-                      THREAD_CONTROL_STACK_SIZE+
-                      BINDING_STACK_SIZE+
-                      ALIEN_STACK_SIZE+
-                      dynamic_values_bytes+
-                      32*SIGSTKSZ);
+                       THREAD_CONTROL_STACK_SIZE+
+                       BINDING_STACK_SIZE+
+                       ALIEN_STACK_SIZE+
+                       dynamic_values_bytes+
+                       32*SIGSTKSZ);
     if(!spaces)
-        return NULL;
+         return NULL;
     per_thread=(union per_thread_data *)
-       (spaces+
-        THREAD_CONTROL_STACK_SIZE+
-        BINDING_STACK_SIZE+
-        ALIEN_STACK_SIZE);
+        (spaces+
+         THREAD_CONTROL_STACK_SIZE+
+         BINDING_STACK_SIZE+
+         ALIEN_STACK_SIZE);
 
     if(all_threads) {
-       memcpy(per_thread,arch_os_get_current_thread(),
-              dynamic_values_bytes);
+        memcpy(per_thread,arch_os_get_current_thread(),
+               dynamic_values_bytes);
     } else {
 #ifdef LISP_FEATURE_SB_THREAD
-       int i;
-       for(i=0;i<(dynamic_values_bytes/sizeof(lispobj));i++)
-           per_thread->dynamic_values[i]=UNBOUND_MARKER_WIDETAG;
-       if(SymbolValue(FREE_TLS_INDEX,0)==UNBOUND_MARKER_WIDETAG) 
-           SetSymbolValue
-               (FREE_TLS_INDEX,
-                make_fixnum(MAX_INTERRUPTS+
-                            sizeof(struct thread)/sizeof(lispobj)),
-                0);
+        int i;
+        for(i=0;i<(dynamic_values_bytes/sizeof(lispobj));i++)
+            per_thread->dynamic_values[i]=UNBOUND_MARKER_WIDETAG;
+        if(SymbolValue(FREE_TLS_INDEX,0)==UNBOUND_MARKER_WIDETAG)
+            SetSymbolValue
+                (FREE_TLS_INDEX,
+                 make_fixnum(MAX_INTERRUPTS+
+                             sizeof(struct thread)/sizeof(lispobj)),
+                 0);
 #define STATIC_TLS_INIT(sym,field) \
   ((struct symbol *)(sym-OTHER_POINTER_LOWTAG))->tls_index= \
   make_fixnum(THREAD_SLOT_OFFSET_WORDS(field))
-                                 
-       STATIC_TLS_INIT(BINDING_STACK_START,binding_stack_start);
-       STATIC_TLS_INIT(BINDING_STACK_POINTER,binding_stack_pointer);
-       STATIC_TLS_INIT(CONTROL_STACK_START,control_stack_start);
-       STATIC_TLS_INIT(CONTROL_STACK_END,control_stack_end);
-       STATIC_TLS_INIT(ALIEN_STACK,alien_stack_pointer);
-#ifdef LISP_FEATURE_X86
-       STATIC_TLS_INIT(PSEUDO_ATOMIC_ATOMIC,pseudo_atomic_atomic);
-       STATIC_TLS_INIT(PSEUDO_ATOMIC_INTERRUPTED,pseudo_atomic_interrupted);
+
+        STATIC_TLS_INIT(BINDING_STACK_START,binding_stack_start);
+        STATIC_TLS_INIT(BINDING_STACK_POINTER,binding_stack_pointer);
+        STATIC_TLS_INIT(CONTROL_STACK_START,control_stack_start);
+        STATIC_TLS_INIT(CONTROL_STACK_END,control_stack_end);
+        STATIC_TLS_INIT(ALIEN_STACK,alien_stack_pointer);
+#if defined(LISP_FEATURE_X86) || defined (LISP_FEATURE_X86_64)
+        STATIC_TLS_INIT(PSEUDO_ATOMIC_ATOMIC,pseudo_atomic_atomic);
+        STATIC_TLS_INIT(PSEUDO_ATOMIC_INTERRUPTED,pseudo_atomic_interrupted);
 #endif
 #undef STATIC_TLS_INIT
 #endif
@@ -136,17 +182,19 @@ struct thread * create_thread_struct(lispobj initial_function) {
     th=&per_thread->thread;
     th->control_stack_start = spaces;
     th->binding_stack_start=
-       (lispobj*)((void*)th->control_stack_start+THREAD_CONTROL_STACK_SIZE);
+        (lispobj*)((void*)th->control_stack_start+THREAD_CONTROL_STACK_SIZE);
     th->control_stack_end = th->binding_stack_start;
     th->alien_stack_start=
-       (lispobj*)((void*)th->binding_stack_start+BINDING_STACK_SIZE);
+        (lispobj*)((void*)th->binding_stack_start+BINDING_STACK_SIZE);
     th->binding_stack_pointer=th->binding_stack_start;
     th->this=th;
-    th->pid=0;
+    th->os_thread=0;
+    th->interrupt_fun=NIL;
+    th->interrupt_fun_lock=0;
     th->state=STATE_STARTING;
 #ifdef LISP_FEATURE_STACK_GROWS_DOWNWARD_NOT_UPWARD
     th->alien_stack_pointer=((void *)th->alien_stack_start
-                            + ALIEN_STACK_SIZE-N_WORD_BYTES);
+                             + ALIEN_STACK_SIZE-N_WORD_BYTES);
 #else
     th->alien_stack_pointer=((void *)th->alien_stack_start);
 #endif
@@ -161,7 +209,7 @@ struct thread * create_thread_struct(lispobj initial_function) {
 #ifndef LISP_FEATURE_SB_THREAD
     /* the tls-points-into-struct-thread trick is only good for threaded
      * sbcl, because unithread sbcl doesn't have tls.  So, we copy the
-     * appropriate values from struct thread here, and make sure that 
+     * appropriate values from struct thread here, and make sure that
      * we use the appropriate SymbolValue macros to access any of the
      * variable quantities from the C runtime.  It's not quite OAOOM,
      * it just feels like it */
@@ -177,213 +225,226 @@ struct thread * create_thread_struct(lispobj initial_function) {
     current_binding_stack_pointer=th->binding_stack_pointer;
     current_control_stack_pointer=th->control_stack_start;
 #endif
-#endif    
+#endif
     bind_variable(CURRENT_CATCH_BLOCK,make_fixnum(0),th);
-    bind_variable(CURRENT_UNWIND_PROTECT_BLOCK,make_fixnum(0),th); 
+    bind_variable(CURRENT_UNWIND_PROTECT_BLOCK,make_fixnum(0),th);
     bind_variable(FREE_INTERRUPT_CONTEXT_INDEX,make_fixnum(0),th);
     bind_variable(INTERRUPT_PENDING, NIL,th);
     bind_variable(INTERRUPTS_ENABLED,T,th);
 
-    th->interrupt_data =
-       os_validate(0,(sizeof (struct interrupt_data)));
-    if(all_threads) 
-       memcpy(th->interrupt_data,
-              arch_os_get_current_thread()->interrupt_data,
-              sizeof (struct interrupt_data));
-    else 
-       memcpy(th->interrupt_data,global_interrupt_data,
-              sizeof (struct interrupt_data));
+    th->interrupt_data = (struct interrupt_data *)
+        os_validate(0,(sizeof (struct interrupt_data)));
+    if(all_threads)
+        memcpy(th->interrupt_data,
+               arch_os_get_current_thread()->interrupt_data,
+               sizeof (struct interrupt_data));
+    else
+        memcpy(th->interrupt_data,global_interrupt_data,
+               sizeof (struct interrupt_data));
 
     th->unbound_marker=initial_function;
     return th;
 }
 
-void link_thread(struct thread *th,pid_t kid_pid)
+void link_thread(struct thread *th,os_thread_t kid_tid)
 {
-    sigset_t newset,oldset;
-    sigemptyset(&newset);
-    sigaddset_blockable(&newset);
-    sigprocmask(SIG_BLOCK, &newset, &oldset); 
-
-    get_spinlock(&all_threads_lock,kid_pid);
+    if (all_threads) all_threads->prev=th;
     th->next=all_threads;
+    th->prev=0;
     all_threads=th;
-    /* note that th->pid is 0 at this time.  We rely on all_threads_lock
-     * to ensure that we don't have >1 thread with pid=0 on the list at once
+    /* note that th->os_thread is 0 at this time.  We rely on
+     * all_threads_lock to ensure that we don't have >1 thread with
+     * os_thread=0 on the list at once
      */
-    protect_control_stack_guard_page(th->pid,1);
-    th->pid=kid_pid;           /* child will not start until this is set */
-    release_spinlock(&all_threads_lock);
-
-    sigprocmask(SIG_SETMASK,&oldset,0);
+    protect_control_stack_guard_page(th,1);
+    /* child will not start until this is set */
+    th->os_thread=kid_tid;
 }
 
 void create_initial_thread(lispobj initial_function) {
     struct thread *th=create_thread_struct(initial_function);
-    pid_t kid_pid=getpid();
-    if(th && kid_pid>0) {
-       link_thread(th,kid_pid);
-       initial_thread_trampoline(all_threads); /* no return */
+    os_thread_t kid_tid=thread_self();
+    if(th && kid_tid>0) {
+        link_thread(th,kid_tid);
+        initial_thread_trampoline(all_threads); /* no return */
     } else lose("can't create initial thread");
 }
 
 #ifdef LISP_FEATURE_SB_THREAD
-pid_t create_thread(lispobj initial_function) {
-    struct thread *th;
-    pid_t kid_pid=0;
 
-    if(linux_no_threads_p) return 0;
-    th=create_thread_struct(initial_function);
-    if(th==0) return 0;
-#ifdef QSHOW_SIGNALS
-    SHOW("create_thread:waiting on lock");
-#endif
-    get_spinlock(&thread_start_lock,arch_os_get_current_thread()->pid);
-#ifdef QSHOW_SIGNALS
-    SHOW("create_thread:got lock");
-#endif
-    kid_pid=clone(new_thread_trampoline,
-                 (((void*)th->control_stack_start)+
-                  THREAD_CONTROL_STACK_SIZE-16),
-                 CLONE_FILES|SIG_THREAD_EXIT|CLONE_VM,th);
-    
-    if(kid_pid>0) {
-       link_thread(th,kid_pid);
-        /* wait here until our thread is started: see new_thread_trampoline */
-        while(th->state==STATE_STARTING) sched_yield();
-        /* it's started and initialized, it's safe to gc */
-        release_spinlock(&thread_start_lock);
-#ifdef QSHOW_SIGNALS
-        SHOW("create_thread:released lock");
-#endif
-       return th->pid;
-    } else {
-        release_spinlock(&thread_start_lock);
-#ifdef QSHOW_SIGNALS
-        SHOW("create_thread:released lock(failure)");
-#endif
-       os_invalidate((os_vm_address_t) th->control_stack_start,
-                     ((sizeof (lispobj))
-                      * (th->control_stack_end-th->control_stack_start)) +
-                     BINDING_STACK_SIZE+ALIEN_STACK_SIZE+dynamic_values_bytes+
-                     32*SIGSTKSZ);
-       return 0;
-    }
+boolean create_os_thread(struct thread *th,os_thread_t *kid_tid)
+{
+    /* The new thread inherits the restrictive signal mask set here,
+     * and enables signals again when it is set up properly. */
+    pthread_attr_t attr;
+    sigset_t newset,oldset;
+    boolean r=1;
+    sigemptyset(&newset);
+    sigaddset_blockable(&newset);
+    thread_sigmask(SIG_BLOCK, &newset, &oldset);
+
+    if((pthread_attr_init(&attr)) ||
+       (pthread_attr_setstack(&attr,th->control_stack_start,
+                              THREAD_CONTROL_STACK_SIZE-16)) ||
+       (pthread_create
+        (kid_tid,&attr,(void *(*)(void *))new_thread_trampoline,th)))
+        r=0;
+    thread_sigmask(SIG_SETMASK,&oldset,0);
+    return r;
 }
-#endif
 
-struct thread *find_thread_by_pid(pid_t pid) 
-{
+struct thread *create_thread(lispobj initial_function) {
     struct thread *th;
-    for_each_thread(th)
-       if(th->pid==pid) return th;
-    return 0;
-}
+    os_thread_t kid_tid=0;
+    boolean success;
 
-#if defined LISP_FEATURE_SB_THREAD
-/* This is not needed unless #+SB-THREAD, as there's a trivial null
- * unithread definition. */
+    if(linux_no_threads_p) return 0;
 
-void mark_dead_threads() 
-{
-    pid_t kid;
-    int status;
-    while(1) {
-       kid=waitpid(-1,&status,__WALL|WNOHANG);
-       if(kid<=0) break;
-       if(WIFEXITED(status) || WIFSIGNALED(status)) {
-           struct thread *th=find_thread_by_pid(kid);
-           if(th) th->state=STATE_DEAD;
-       }
-    }
+    th=create_thread_struct(initial_function);
+    if(th==0) return 0;
+
+    /* we must not be interrupted here after a successful
+     * create_os_thread, because the kid will be waiting for its
+     * thread struct to be linked */
+    GET_ALL_THREADS_LOCK("create_thread")
+
+    success=create_os_thread(th,&kid_tid);
+    if (success)
+        link_thread(th,kid_tid);
+    else
+        os_invalidate((os_vm_address_t) th->control_stack_start,
+                      ((sizeof (lispobj))
+                       * (th->control_stack_end-th->control_stack_start)) +
+                      BINDING_STACK_SIZE+ALIEN_STACK_SIZE+dynamic_values_bytes+
+                      32*SIGSTKSZ);
+
+    RELEASE_ALL_THREADS_LOCK("create_thread")
+
+    if (success)
+        return th;
+    else
+        return 0;
 }
 
-void reap_dead_threads() 
+/* called from lisp from the thread object finalizer */
+void reap_dead_thread(struct thread *th)
 {
-    struct thread *th,*next,*prev=0;
-    th=all_threads;
-    while(th) {
-       next=th->next;
-       if(th->state==STATE_DEAD) {
-           funcall1(SymbolFunction(HANDLE_THREAD_EXIT),make_fixnum(th->pid));
+    if(th->state!=STATE_DEAD)
+        lose("thread %lx is not joinable, state=%d\n",th,th->state);
 #ifdef LISP_FEATURE_GENCGC
-           gc_alloc_update_page_tables(0, &th->alloc_region);
-#endif
-           get_spinlock(&all_threads_lock,th->pid);
-           if(prev) prev->next=next;
-           else all_threads=next;
-           release_spinlock(&all_threads_lock);
-           if(th->tls_cookie>=0) arch_os_thread_cleanup(th); 
-           os_invalidate((os_vm_address_t) th->control_stack_start,
-                         ((sizeof (lispobj))
-                          * (th->control_stack_end-th->control_stack_start)) +
-                         BINDING_STACK_SIZE+ALIEN_STACK_SIZE+dynamic_values_bytes+
-                         32*SIGSTKSZ);
-       } else 
-           prev=th;
-       th=next;
+    {
+        sigset_t newset,oldset;
+        sigemptyset(&newset);
+        sigaddset_blockable(&newset);
+        thread_sigmask(SIG_BLOCK, &newset, &oldset);
+        gc_alloc_update_page_tables(0, &th->alloc_region);
+        release_spinlock(&all_threads_lock);
+        thread_sigmask(SIG_SETMASK,&oldset,0);
     }
+#endif
+    GET_ALL_THREADS_LOCK("reap_dead_thread")
+    FSHOW((stderr,"/reap_dead_thread: reaping %ld\n",th->os_thread));
+    if(th->prev)
+        th->prev->next=th->next;
+    else all_threads=th->next;
+    if(th->next)
+        th->next->prev=th->prev;
+    RELEASE_ALL_THREADS_LOCK("reap_dead_thread")
+    if(th->tls_cookie>=0) arch_os_thread_cleanup(th);
+    gc_assert(pthread_join(th->os_thread,NULL)==0);
+    os_invalidate((os_vm_address_t) th->control_stack_start,
+                  ((sizeof (lispobj))
+                   * (th->control_stack_end-th->control_stack_start)) +
+                  BINDING_STACK_SIZE+ALIEN_STACK_SIZE+dynamic_values_bytes+
+                  32*SIGSTKSZ);
 }
 
-int interrupt_thread(pid_t pid, lispobj function)
+int interrupt_thread(struct thread *th, lispobj function)
 {
-    union sigval sigval;
-    struct thread *th;
-    sigval.sival_int=function;
-    for_each_thread(th) 
-       if((th->pid==pid) && (th->state != STATE_DEAD))
-           return sigqueue(pid, SIG_INTERRUPT_THREAD, sigval);
+    /* A thread may also become dead after this test. */
+    if ((th->state != STATE_DEAD)) {
+        /* In clone_threads, if A and B both interrupt C at
+         * approximately the same time, it does not matter: the
+         * second signal will be masked until the handler has
+         * returned from the first one.  In pthreads though, we
+         * can't put the knowledge of what function to call into
+         * the siginfo, so we have to store it in the destination
+         * thread, and do it in such a way that A won't clobber
+         * B's interrupt.  Hence this stupid linked list.
+         *
+         * This does depend on SIG_INTERRUPT_THREAD being queued
+         * (as POSIX RT signals are): we need to keep
+         * interrupt_fun data for exactly as many signals as are
+         * going to be received by the destination thread.
+         */
+        struct cons *c=alloc_cons(function,NIL);
+        int kill_status;
+        /* interrupt_thread_handler locks this spinlock with
+         * interrupts blocked and it does so for the sake of
+         * arrange_return_to_lisp_function, so we must also block
+         * them. */
+        sigset_t newset,oldset;
+        sigemptyset(&newset);
+        sigaddset_blockable(&newset);
+        thread_sigmask(SIG_BLOCK, &newset, &oldset);
+        get_spinlock(&th->interrupt_fun_lock,
+                     (long)arch_os_get_current_thread());
+        kill_status=thread_kill(th->os_thread,SIG_INTERRUPT_THREAD);
+        if(kill_status==0) {
+            ((struct cons *)native_pointer(c))->cdr=th->interrupt_fun;
+            th->interrupt_fun=c;
+        }
+        release_spinlock(&th->interrupt_fun_lock);
+        thread_sigmask(SIG_SETMASK,&oldset,0);
+        return (kill_status ? -1 : 0);
+    }
     errno=EPERM; return -1;
 }
 
-int signal_thread_to_dequeue (pid_t pid)
-{
-    return kill (pid, SIG_DEQUEUE);
-}
-
-
-/* stopping the world is a two-stage process.  From this thread we signal 
+/* stopping the world is a two-stage process.  From this thread we signal
  * all the others with SIG_STOP_FOR_GC.  The handler for this signal does
- * the usual pseudo-atomic checks (we don't want to stop a thread while 
+ * the usual pseudo-atomic checks (we don't want to stop a thread while
  * it's in the middle of allocation) then waits for another SIG_STOP_FOR_GC.
  */
 
+/* To avoid deadlocks when gc stops the world all clients of each
+ * mutex must enable or disable SIG_STOP_FOR_GC for the duration of
+ * holding the lock, but they must agree on which. */
 void gc_stop_the_world()
 {
-#ifdef QSHOW_SIGNALS
-    SHOW("gc_stop_the_world:begin");
-#endif
     struct thread *p,*th=arch_os_get_current_thread();
+    FSHOW_SIGNAL((stderr,"/gc_stop_the_world:waiting on lock, thread=%ld\n",
+                  th->os_thread));
     /* keep threads from starting while the world is stopped. */
-    get_spinlock(&thread_start_lock,th->pid);
-#ifdef QSHOW_SIGNALS
-    SHOW("gc_stop_the_world:locked");
-#endif
+    get_spinlock(&all_threads_lock,(long)th);
+    FSHOW_SIGNAL((stderr,"/gc_stop_the_world:got lock, thread=%ld\n",
+                  th->os_thread));
     /* stop all other threads by sending them SIG_STOP_FOR_GC */
     for(p=all_threads; p; p=p->next) {
-        if((p!=th) && (p->pid!=0) && (p->state==STATE_RUNNING)) {
-            p->state=STATE_STOPPING;
-            if(kill(p->pid,SIG_STOP_FOR_GC)==-1) {
-                /* we can't kill the process; assume because it
-                 * died already (and its parent is dead so never
-                 * saw the SIGCHLD) */
+        while(p->state==STATE_STARTING) sched_yield();
+        if((p!=th) && (p->state==STATE_RUNNING)) {
+            FSHOW_SIGNAL((stderr,"/gc_stop_the_world:sending sig_stop to %ld\n",
+                          p->os_thread));
+            if(thread_kill(p->os_thread,SIG_STOP_FOR_GC)==-1) {
+                /* we can't kill the thread; assume because it died
+                 * since we last checked */
                 p->state=STATE_DEAD;
+                FSHOW_SIGNAL((stderr,"/gc_stop_the_world:assuming %ld dead\n",
+                   p->os_thread));
             }
         }
     }
-#ifdef QSHOW_SIGNALS
-    SHOW("gc_stop_the_world:signals sent");
-#endif
-    /* wait for the running threads to stop */
+    FSHOW_SIGNAL((stderr,"/gc_stop_the_world:signals sent\n"));
+    /* wait for the running threads to stop or finish */
     for(p=all_threads;p;) {
-        if((p==th) || (p->pid==0) || (p->state==STATE_STARTING) ||
-           (p->state==STATE_DEAD) || (p->state==STATE_STOPPED)) {
+        gc_assert(p->os_thread!=0);
+        gc_assert(p->state!=STATE_STARTING);
+        if((p==th) || (p->state==STATE_SUSPENDED) ||
+           (p->state==STATE_DEAD)) {
             p=p->next;
         }
     }
-#ifdef QSHOW_SIGNALS
-    SHOW("gc_stop_the_world:end");
-#endif
+    FSHOW_SIGNAL((stderr,"/gc_stop_the_world:end\n"));
 }
 
 void gc_start_the_world()
@@ -392,33 +453,27 @@ void gc_start_the_world()
     /* if a resumed thread creates a new thread before we're done with
      * this loop, the new thread will get consed on the front of
      * all_threads, but it won't have been stopped so won't need
-     * restarting; there can be threads just starting from before
-     * gc_stop_the_world, though */
-#ifdef QSHOW_SIGNALS
-    SHOW("gc_start_the_world:begin");
-#endif
+     * restarting */
+    FSHOW_SIGNAL((stderr,"/gc_start_the_world:begin\n"));
     for(p=all_threads;p;p=p->next) {
-       if((p!=th) && (p->pid!=0) && (p->state!=STATE_STARTING) &&
-           (p->state!=STATE_DEAD)) {
-            if(p->state!=STATE_STOPPED) {
+        gc_assert(p->os_thread!=0);
+        if((p!=th) && (p->state!=STATE_DEAD)) {
+            if(p->state!=STATE_SUSPENDED) {
                 lose("gc_start_the_world: wrong thread state is %ld\n",
                      fixnum_value(p->state));
             }
-            kill(p->pid,SIG_STOP_FOR_GC);
+            thread_kill(p->os_thread,SIG_STOP_FOR_GC);
         }
     }
     /* we must wait for all threads to leave stopped state else we
      * risk signal accumulation and lose any meaning of
      * thread->state */
     for(p=all_threads;p;) {
-        gc_assert(p->state!=STATE_STOPPING);
-        if((p==th) || (p->pid==0) || (p->state!=STATE_STOPPED)) {
+        if((p==th) || (p->state!=STATE_SUSPENDED)) {
             p=p->next;
         }
     }
-    release_spinlock(&thread_start_lock);
-#ifdef QSHOW_SIGNALS
-    SHOW("gc_start_the_world:end");
-#endif
+    release_spinlock(&all_threads_lock);
+    FSHOW_SIGNAL((stderr,"/gc_start_the_world:end\n"));
 }
 #endif