1.0.25.37: block deferrables when gc pending in PA
[sbcl.git] / src / runtime / thread.c
index 0bc37a2..8e6c3c2 100644 (file)
@@ -32,7 +32,7 @@
 #endif
 
 #include "runtime.h"
-#include "validate.h"           /* for CONTROL_STACK_SIZE etc */
+#include "validate.h"           /* for BINDING_STACK_SIZE etc */
 #include "alloc.h"
 #include "thread.h"
 #include "arch.h"
@@ -54,7 +54,7 @@
 #endif
 
 #if defined(LISP_FEATURE_DARWIN) && defined(LISP_FEATURE_SB_THREAD)
-#define QUEUE_FREEABLE_THREAD_STACKS
+#define DELAY_THREAD_POST_MORTEM 5
 #define LOCK_CREATE_THREAD
 #endif
 
 
 #define ALIEN_STACK_SIZE (1*1024*1024) /* 1Mb size chosen at random */
 
-struct freeable_stack {
-#ifdef QUEUE_FREEABLE_THREAD_STACKS
-    struct freeable_stack *next;
+#ifdef LISP_FEATURE_SB_THREAD
+struct thread_post_mortem {
+#ifdef DELAY_THREAD_POST_MORTEM
+    struct thread_post_mortem *next;
 #endif
     os_thread_t os_thread;
-    os_vm_address_t stack;
+    pthread_attr_t *os_attr;
+    os_vm_address_t os_address;
 };
 
-
-#ifdef QUEUE_FREEABLE_THREAD_STACKS
-static struct freeable_stack * volatile freeable_stack_queue = 0;
-static int freeable_stack_count = 0;
-pthread_mutex_t freeable_stack_lock = PTHREAD_MUTEX_INITIALIZER;
-#else
-static struct freeable_stack * volatile freeable_stack = 0;
+#ifdef DELAY_THREAD_POST_MORTEM
+static int pending_thread_post_mortem_count = 0;
+pthread_mutex_t thread_post_mortem_lock = PTHREAD_MUTEX_INITIALIZER;
+#endif
+static struct thread_post_mortem * volatile pending_thread_post_mortem = 0;
 #endif
 
-int dynamic_values_bytes=4096*sizeof(lispobj);  /* same for all threads */
-struct thread * volatile all_threads;
+int dynamic_values_bytes=TLS_SIZE*sizeof(lispobj);  /* same for all threads */
+struct thread *all_threads;
 extern struct interrupt_data * global_interrupt_data;
 
 #ifdef LISP_FEATURE_SB_THREAD
@@ -91,6 +91,9 @@ pthread_mutex_t all_threads_lock = PTHREAD_MUTEX_INITIALIZER;
 #ifdef LOCK_CREATE_THREAD
 static pthread_mutex_t create_thread_lock = PTHREAD_MUTEX_INITIALIZER;
 #endif
+#ifdef LISP_FEATURE_GCC_TLS
+__thread struct thread *current_thread;
+#endif
 #endif
 
 #if defined(LISP_FEATURE_X86) || defined(LISP_FEATURE_X86_64)
@@ -142,132 +145,106 @@ initial_thread_trampoline(struct thread *th)
 #endif
 }
 
-#define THREAD_STRUCT_SIZE (THREAD_CONTROL_STACK_SIZE + BINDING_STACK_SIZE + \
-                            ALIEN_STACK_SIZE + dynamic_values_bytes + \
-                            32 * SIGSTKSZ)
-
 #ifdef LISP_FEATURE_SB_THREAD
+#define THREAD_STATE_LOCK_SIZE \
+    (sizeof(pthread_mutex_t))+(sizeof(pthread_cond_t))
+#else
+#define THREAD_STATE_LOCK_SIZE 0
+#endif
 
-#ifdef QUEUE_FREEABLE_THREAD_STACKS
+#define THREAD_STRUCT_SIZE (thread_control_stack_size + BINDING_STACK_SIZE + \
+                            ALIEN_STACK_SIZE +                               \
+                            THREAD_STATE_LOCK_SIZE +                         \
+                            dynamic_values_bytes +                           \
+                            32 * SIGSTKSZ +                                  \
+                            THREAD_ALIGNMENT_BYTES)
 
-static void
-queue_freeable_thread_stack(struct thread *thread_to_be_cleaned_up)
+#ifdef LISP_FEATURE_SB_THREAD
+/* THREAD POST MORTEM CLEANUP
+ *
+ * Memory allocated for the thread stacks cannot be reclaimed while
+ * the thread is still alive, so we need a mechanism for post mortem
+ * cleanups. FIXME: We actually have three, for historical reasons as
+ * the saying goes. Do we really need three? Nikodemus guesses that
+ * not anymore, now that we properly call pthread_attr_destroy before
+ * freeing the stack. */
+
+static struct thread_post_mortem *
+plan_thread_post_mortem(struct thread *corpse)
 {
-     if (thread_to_be_cleaned_up) {
-        pthread_mutex_lock(&freeable_stack_lock);
-        if (freeable_stack_queue) {
-            struct freeable_stack *new_freeable_stack = 0, *next;
-            next = freeable_stack_queue;
-            while (next->next) {
-                next = next->next;
-            }
-            new_freeable_stack = (struct freeable_stack *)
-                os_validate(0, sizeof(struct freeable_stack));
-            new_freeable_stack->next = NULL;
-            new_freeable_stack->os_thread = thread_to_be_cleaned_up->os_thread;
-            new_freeable_stack->stack = (os_vm_address_t)
-                thread_to_be_cleaned_up->control_stack_start;
-            next->next = new_freeable_stack;
-            freeable_stack_count++;
-        } else {
-            struct freeable_stack *new_freeable_stack = 0;
-            new_freeable_stack = (struct freeable_stack *)
-                os_validate(0, sizeof(struct freeable_stack));
-            new_freeable_stack->next = NULL;
-            new_freeable_stack->os_thread = thread_to_be_cleaned_up->os_thread;
-            new_freeable_stack->stack = (os_vm_address_t)
-                thread_to_be_cleaned_up->control_stack_start;
-            freeable_stack_queue = new_freeable_stack;
-            freeable_stack_count++;
-        }
-        pthread_mutex_unlock(&freeable_stack_lock);
-    }
-}
-
-#define FREEABLE_STACK_QUEUE_SIZE 4
-
-static void
-free_freeable_stacks() {
-    if (freeable_stack_queue && (freeable_stack_count > FREEABLE_STACK_QUEUE_SIZE)) {
-        struct freeable_stack* old;
-        pthread_mutex_lock(&freeable_stack_lock);
-        old = freeable_stack_queue;
-        freeable_stack_queue = old->next;
-        freeable_stack_count--;
-        gc_assert(pthread_join(old->os_thread, NULL) == 0);
-        FSHOW((stderr, "freeing thread %x stack\n", old->os_thread));
-        os_invalidate(old->stack, THREAD_STRUCT_SIZE);
-        os_invalidate((os_vm_address_t)old, sizeof(struct freeable_stack));
-        pthread_mutex_unlock(&freeable_stack_lock);
+    if (corpse) {
+        struct thread_post_mortem *post_mortem = malloc(sizeof(struct thread_post_mortem));
+        gc_assert(post_mortem);
+        post_mortem->os_thread = corpse->os_thread;
+        post_mortem->os_attr = corpse->os_attr;
+        post_mortem->os_address = corpse->os_address;
+#ifdef DELAY_THREAD_POST_MORTEM
+        post_mortem->next = NULL;
+#endif
+        return post_mortem;
+    } else {
+        /* FIXME: When does this happen? */
+        return NULL;
     }
 }
 
-#elif defined(CREATE_CLEANUP_THREAD)
-static void *
-cleanup_thread(void *arg)
-{
-    struct freeable_stack *freeable = arg;
-    pthread_t self = pthread_self();
-
-    FSHOW((stderr, "/cleaner thread(%p): joining %p\n",
-           self, freeable->os_thread));
-    gc_assert(pthread_join(freeable->os_thread, NULL) == 0);
-    FSHOW((stderr, "/cleaner thread(%p): free stack %p\n",
-           self, freeable->stack));
-    os_invalidate(freeable->stack, THREAD_STRUCT_SIZE);
-    free(freeable);
-
-    pthread_detach(self);
-
-    return NULL;
-}
-
 static void
-create_cleanup_thread(struct thread *thread_to_be_cleaned_up)
+perform_thread_post_mortem(struct thread_post_mortem *post_mortem)
 {
-    pthread_t thread;
-    int result;
-
-    if (thread_to_be_cleaned_up) {
-        struct freeable_stack *freeable =
-            malloc(sizeof(struct freeable_stack));
-        gc_assert(freeable != NULL);
-        freeable->os_thread = thread_to_be_cleaned_up->os_thread;
-        freeable->stack =
-            (os_vm_address_t) thread_to_be_cleaned_up->control_stack_start;
-        result = pthread_create(&thread, NULL, cleanup_thread, freeable);
-        gc_assert(result == 0);
-        sched_yield();
+#ifdef CREATE_POST_MORTEM_THREAD
+    pthread_detach(pthread_self());
+#endif
+    if (post_mortem) {
+        gc_assert(!pthread_join(post_mortem->os_thread, NULL));
+        gc_assert(!pthread_attr_destroy(post_mortem->os_attr));
+        free(post_mortem->os_attr);
+        os_invalidate(post_mortem->os_address, THREAD_STRUCT_SIZE);
+        free(post_mortem);
     }
 }
 
-#else
 static void
-free_thread_stack_later(struct thread *thread_to_be_cleaned_up)
+schedule_thread_post_mortem(struct thread *corpse)
 {
-    struct freeable_stack *new_freeable_stack = 0;
-    if (thread_to_be_cleaned_up) {
-        new_freeable_stack = (struct freeable_stack *)
-            os_validate(0, sizeof(struct freeable_stack));
-        new_freeable_stack->os_thread = thread_to_be_cleaned_up->os_thread;
-        new_freeable_stack->stack = (os_vm_address_t)
-            thread_to_be_cleaned_up->control_stack_start;
-    }
-    new_freeable_stack = (struct freeable_stack *)
-        swap_lispobjs((lispobj *)(void *)&freeable_stack,
-                      (lispobj)new_freeable_stack);
-    if (new_freeable_stack) {
-        FSHOW((stderr,"/reaping %p\n", (void*) new_freeable_stack->os_thread));
-        /* Under NPTL pthread_join really waits until the thread
-         * exists and the stack can be safely freed. This is sadly not
-         * mandated by the pthread spec. */
-        gc_assert(pthread_join(new_freeable_stack->os_thread, NULL) == 0);
-        os_invalidate(new_freeable_stack->stack, THREAD_STRUCT_SIZE);
-        os_invalidate((os_vm_address_t) new_freeable_stack,
-                      sizeof(struct freeable_stack));
+    struct thread_post_mortem *post_mortem = NULL;
+    if (corpse) {
+        post_mortem = plan_thread_post_mortem(corpse);
+
+#ifdef DELAY_THREAD_POST_MORTEM
+        pthread_mutex_lock(&thread_post_mortem_lock);
+        /* First stick the new post mortem to the end of the queue. */
+        if (pending_thread_post_mortem) {
+            struct thread_post_mortem *next = pending_thread_post_mortem;
+            while (next->next) {
+                next = next->next;
+            }
+            next->next = post_mortem;
+        } else {
+            pending_thread_post_mortem = post_mortem;
+        }
+        /* Then, if there are enough things in the queue, clean up one
+         * from the head -- or increment the count, and null out the
+         * post_mortem we have. */
+        if (pending_thread_post_mortem_count > DELAY_THREAD_POST_MORTEM) {
+            post_mortem = pending_thread_post_mortem;
+            pending_thread_post_mortem = post_mortem->next;
+        } else {
+            pending_thread_post_mortem_count++;
+            post_mortem = NULL;
+        }
+        pthread_mutex_unlock(&thread_post_mortem_lock);
+        /* Finally run, the cleanup, if any. */
+        perform_thread_post_mortem(post_mortem);
+#elif defined(CREATE_POST_MORTEM_THREAD)
+        gc_assert(!pthread_create(&thread, NULL, perform_thread_post_mortem, post_mortem));
+#else
+        post_mortem = (struct thread_post_mortem *)
+            swap_lispobjs((lispobj *)(void *)&pending_thread_post_mortem,
+                          (lispobj)post_mortem);
+        perform_thread_post_mortem(post_mortem);
+#endif
     }
 }
-#endif
 
 /* this is the first thing that runs in the child (which is why the
  * silly calling convention).  Basically it calls the user's requested
@@ -304,19 +281,22 @@ new_thread_trampoline(struct thread *th)
 
     /* Block GC */
     block_blockable_signals();
-    th->state=STATE_DEAD;
+    set_thread_state(th, STATE_DEAD);
 
     /* SIG_STOP_FOR_GC is blocked and GC might be waiting for this
      * thread, but since we are already dead it won't wait long. */
     lock_ret = pthread_mutex_lock(&all_threads_lock);
     gc_assert(lock_ret == 0);
 
-    gc_alloc_update_page_tables(0, &th->alloc_region);
+    gc_alloc_update_page_tables(BOXED_PAGE_FLAG, &th->alloc_region);
     unlink_thread(th);
     pthread_mutex_unlock(&all_threads_lock);
     gc_assert(lock_ret == 0);
 
     if(th->tls_cookie>=0) arch_os_thread_cleanup(th);
+    pthread_mutex_destroy(th->state_lock);
+    pthread_cond_destroy(th->state_cond);
+
     os_invalidate((os_vm_address_t)th->interrupt_data,
                   (sizeof (struct interrupt_data)));
 
@@ -331,15 +311,8 @@ new_thread_trampoline(struct thread *th)
                       THREAD_STRUCT_TO_EXCEPTION_PORT(th));
 #endif
 
-#ifdef QUEUE_FREEABLE_THREAD_STACKS
-    queue_freeable_thread_stack(th);
-#elif defined(CREATE_CLEANUP_THREAD)
-    create_cleanup_thread(th);
-#else
-    free_thread_stack_later(th);
-#endif
-
-    FSHOW((stderr,"/exiting thread %p\n", thread_self()));
+    schedule_thread_post_mortem(th);
+    FSHOW((stderr,"/exiting thread %lu\n", thread_self()));
     return result;
 }
 
@@ -351,7 +324,7 @@ free_thread_struct(struct thread *th)
     if (th->interrupt_data)
         os_invalidate((os_vm_address_t) th->interrupt_data,
                       (sizeof (struct interrupt_data)));
-    os_invalidate((os_vm_address_t) th->control_stack_start,
+    os_invalidate((os_vm_address_t) th->os_address,
                   THREAD_STRUCT_SIZE);
 }
 
@@ -365,25 +338,33 @@ create_thread_struct(lispobj initial_function) {
     union per_thread_data *per_thread;
     struct thread *th=0;        /*  subdue gcc */
     void *spaces=0;
+    void *aligned_spaces=0;
 #ifdef LISP_FEATURE_SB_THREAD
-    int i;
+    unsigned int i;
 #endif
 
-#ifdef CREATE_CLEANUP_THREAD
-    /* Give a chance for cleanup threads to run. */
-    sched_yield();
-#endif
-    /* may as well allocate all the spaces at once: it saves us from
+    /* 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 */
+     * succeed. SPACES must be appropriately aligned, since the GC
+     * expects the control stack to start at a page boundary -- and
+     * the OS may have even more rigorous requirements. We can't rely
+     * on the alignment passed from os_validate, since that might
+     * assume the current (e.g. 4k) pagesize, while we calculate with
+     * the biggest (e.g. 64k) pagesize allowed by the ABI. */
     spaces=os_validate(0, THREAD_STRUCT_SIZE);
     if(!spaces)
-         return NULL;
+        return NULL;
+    /* Aligning up is safe as THREAD_STRUCT_SIZE has
+     * THREAD_ALIGNMENT_BYTES padding. */
+    aligned_spaces = (void *)((((unsigned long)(char *)spaces)
+                               + THREAD_ALIGNMENT_BYTES-1)
+                              &~(unsigned long)(THREAD_ALIGNMENT_BYTES-1));
     per_thread=(union per_thread_data *)
-        (spaces+
-         THREAD_CONTROL_STACK_SIZE+
+        (aligned_spaces+
+         thread_control_stack_size+
          BINDING_STACK_SIZE+
-         ALIEN_STACK_SIZE);
+         ALIEN_STACK_SIZE +
+         THREAD_STATE_LOCK_SIZE);
 
 #ifdef LISP_FEATURE_SB_THREAD
     for(i = 0; i < (dynamic_values_bytes / sizeof(lispobj)); i++)
@@ -415,15 +396,25 @@ create_thread_struct(lispobj initial_function) {
 #endif
 
     th=&per_thread->thread;
-    th->control_stack_start = spaces;
+    th->os_address = spaces;
+    th->control_stack_start = aligned_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);
     th->binding_stack_pointer=th->binding_stack_start;
     th->this=th;
     th->os_thread=0;
+#ifdef LISP_FEATURE_SB_THREAD
+    th->os_attr=malloc(sizeof(pthread_attr_t));
+    th->state_lock=(pthread_mutex_t *)((void *)th->alien_stack_start +
+                                       ALIEN_STACK_SIZE);
+    pthread_mutex_init(th->state_lock, NULL);
+    th->state_cond=(pthread_cond_t *)((void *)th->state_lock +
+                                      (sizeof(pthread_mutex_t)));
+    pthread_cond_init(th->state_cond, NULL);
+#endif
     th->state=STATE_RUNNING;
 #ifdef LISP_FEATURE_STACK_GROWS_DOWNWARD_NOT_UPWARD
     th->alien_stack_pointer=((void *)th->alien_stack_start
@@ -464,6 +455,7 @@ create_thread_struct(lispobj initial_function) {
     bind_variable(INTERRUPTS_ENABLED,T,th);
     bind_variable(ALLOW_WITH_INTERRUPTS,T,th);
     bind_variable(GC_PENDING,NIL,th);
+    bind_variable(ALLOC_SIGNAL,NIL,th);
 #ifdef LISP_FEATURE_SB_THREAD
     bind_variable(STOP_FOR_GC_PENDING,NIL,th);
 #endif
@@ -475,6 +467,7 @@ create_thread_struct(lispobj initial_function) {
         return 0;
     }
     th->interrupt_data->pending_handler = 0;
+    th->interrupt_data->gc_blocked_deferrables = 0;
     th->no_tls_value_marker=initial_function;
 
     th->stepping = NIL;
@@ -491,8 +484,6 @@ void create_initial_thread(lispobj initial_function) {
     struct thread *th=create_thread_struct(initial_function);
     if(th) {
 #ifdef LISP_FEATURE_MACH_EXCEPTION_HANDLER
-        kern_return_t ret;
-
         setup_mach_exception_handling_thread();
 #endif
         initial_thread_trampoline(th); /* no return */
@@ -510,10 +501,9 @@ 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;
-    int retcode, initcode, sizecode, addrcode;
+    int retcode = 0, initcode;
 
     FSHOW_SIGNAL((stderr,"/create_os_thread: creating new thread\n"));
 
@@ -529,32 +519,20 @@ boolean create_os_thread(struct thread *th,os_thread_t *kid_tid)
     sigaddset_deferrable(&newset);
     thread_sigmask(SIG_BLOCK, &newset, &oldset);
 
-#if defined(LISP_FEATURE_DARWIN)
-#define CONTROL_STACK_ADJUST 8192 /* darwin wants page-aligned stacks */
-#else
-#define CONTROL_STACK_ADJUST 16
-#endif
-
-    if((initcode = pthread_attr_init(&attr)) ||
-       /* FIXME: why do we even have this in the first place? */
-       (pthread_attr_setstack(&attr,th->control_stack_start,
-                              THREAD_CONTROL_STACK_SIZE-CONTROL_STACK_ADJUST)) ||
-#undef CONTROL_STACK_ADJUST
+    if((initcode = pthread_attr_init(th->os_attr)) ||
+       /* call_into_lisp_first_time switches the stack for the initial thread. For the
+        * others, we use this. */
+       (pthread_attr_setstack(th->os_attr,th->control_stack_start,thread_control_stack_size)) ||
        (retcode = pthread_create
-        (kid_tid,&attr,(void *(*)(void *))new_thread_trampoline,th))) {
-        FSHOW_SIGNAL((stderr, "init, size, addr = %d, %d, %d\n", initcode, sizecode, addrcode));
+        (kid_tid,th->os_attr,(void *(*)(void *))new_thread_trampoline,th))) {
+        FSHOW_SIGNAL((stderr, "init = %d\n", initcode));
         FSHOW_SIGNAL((stderr, printf("pthread_create returned %d, errno %d\n", retcode, errno)));
-        FSHOW_SIGNAL((stderr, "wanted stack size %d, min stack size %d\n",
-                      THREAD_CONTROL_STACK_SIZE-16, PTHREAD_STACK_MIN));
         if(retcode < 0) {
             perror("create_os_thread");
         }
         r=0;
     }
 
-#ifdef QUEUE_FREEABLE_THREAD_STACKS
-    free_freeable_stacks();
-#endif
     thread_sigmask(SIG_SETMASK,&oldset,0);
 #ifdef LOCK_CREATE_THREAD
     retcode = pthread_mutex_unlock(&create_thread_lock);
@@ -583,31 +561,10 @@ os_thread_t create_thread(lispobj initial_function) {
     }
 }
 
-/* Send the signo to os_thread, retry if the rt signal queue is
- * full. */
-int
-kill_thread_safely(os_thread_t os_thread, int signo)
-{
-    int r;
-    /* The man page does not mention EAGAIN as a valid return value
-     * for either pthread_kill or kill. But that's theory, this is
-     * practice. By waiting here we assume that the delivery of this
-     * signal is not necessary for the delivery of the signals in the
-     * queue. In other words, we _assume_ there are no deadlocks. */
-    while ((r=pthread_kill(os_thread,signo))==EAGAIN) {
-        /* wait a bit then try again in the hope of the rt signal
-         * queue not being full */
-        FSHOW_SIGNAL((stderr,"/rt signal queue full\n"));
-        /* FIXME: some kind of backoff (random, exponential) would be
-         * nice. */
-        sleep(1);
-    }
-    return r;
-}
-
 int signal_interrupt_thread(os_thread_t os_thread)
 {
-    int status = kill_thread_safely(os_thread, SIG_INTERRUPT_THREAD);
+    int status = pthread_kill(os_thread, SIG_INTERRUPT_THREAD);
+    FSHOW_SIGNAL((stderr,"/signal_interrupt_thread: %lu\n", os_thread));
     if (status == 0) {
         return 0;
     } else if (status == ESRCH) {
@@ -634,32 +591,29 @@ void gc_stop_the_world()
 #ifdef LOCK_CREATE_THREAD
     /* KLUDGE: Stopping the thread during pthread_create() causes deadlock
      * on FreeBSD. */
-    FSHOW_SIGNAL((stderr,"/gc_stop_the_world:waiting on create_thread_lock, thread=%lu\n",
-                  th->os_thread));
+    FSHOW_SIGNAL((stderr,"/gc_stop_the_world:waiting on create_thread_lock\n"));
     lock_ret = pthread_mutex_lock(&create_thread_lock);
     gc_assert(lock_ret == 0);
-    FSHOW_SIGNAL((stderr,"/gc_stop_the_world:got create_thread_lock, thread=%lu\n",
-                  th->os_thread));
+    FSHOW_SIGNAL((stderr,"/gc_stop_the_world:got create_thread_lock\n"));
 #endif
-    FSHOW_SIGNAL((stderr,"/gc_stop_the_world:waiting on lock, thread=%lu\n",
-                  th->os_thread));
+    FSHOW_SIGNAL((stderr,"/gc_stop_the_world:waiting on lock\n"));
     /* keep threads from starting while the world is stopped. */
     lock_ret = pthread_mutex_lock(&all_threads_lock);      \
     gc_assert(lock_ret == 0);
 
-    FSHOW_SIGNAL((stderr,"/gc_stop_the_world:got lock, thread=%lu\n",
-                  th->os_thread));
+    FSHOW_SIGNAL((stderr,"/gc_stop_the_world:got lock\n"));
     /* stop all other threads by sending them SIG_STOP_FOR_GC */
     for(p=all_threads; p; p=p->next) {
         gc_assert(p->os_thread != 0);
-        FSHOW_SIGNAL((stderr,"/gc_stop_the_world: p->state: %x\n", p->state));
-        if((p!=th) && ((p->state==STATE_RUNNING))) {
-            FSHOW_SIGNAL((stderr,"/gc_stop_the_world: suspending %x, os_thread %x\n",
-                          p, p->os_thread));
-            status=kill_thread_safely(p->os_thread,SIG_STOP_FOR_GC);
+        FSHOW_SIGNAL((stderr,"/gc_stop_the_world: thread=%lu, state=%x\n",
+                      p->os_thread, thread_state(p)));
+        if((p!=th) && ((thread_state(p)==STATE_RUNNING))) {
+            FSHOW_SIGNAL((stderr,"/gc_stop_the_world: suspending thread %lu\n",
+                          p->os_thread));
+            status=pthread_kill(p->os_thread,SIG_STOP_FOR_GC);
             if (status==ESRCH) {
                 /* This thread has exited. */
-                gc_assert(p->state==STATE_DEAD);
+                gc_assert(thread_state(p)==STATE_DEAD);
             } else if (status) {
                 lose("cannot send suspend thread=%lu: %d, %s\n",
                      p->os_thread,status,strerror(status));
@@ -667,13 +621,15 @@ void gc_stop_the_world()
         }
     }
     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:signals sent\n"));
-    /* wait for the running threads to stop or finish */
-    for(p=all_threads;p;) {
-        FSHOW_SIGNAL((stderr,"/gc_stop_the_world: th: %p, p: %p\n", th, p));
-        if((p!=th) && (p->state==STATE_RUNNING)) {
-            sched_yield();
-        } else {
-            p=p->next;
+    for(p=all_threads;p;p=p->next) {
+        if (p!=th) {
+            FSHOW_SIGNAL
+                ((stderr,
+                  "/gc_stop_the_world: waiting for thread=%lu: state=%x\n",
+                  p->os_thread, thread_state(p)));
+            wait_for_thread_state_change(p, STATE_RUNNING);
+            if (p->state == STATE_RUNNING)
+                lose("/gc_stop_the_world: unexpected state");
         }
     }
     FSHOW_SIGNAL((stderr,"/gc_stop_the_world:end\n"));
@@ -682,7 +638,7 @@ void gc_stop_the_world()
 void gc_start_the_world()
 {
     struct thread *p,*th=arch_os_get_current_thread();
-    int status, lock_ret;
+    int lock_ret;
     /* 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
@@ -690,30 +646,19 @@ void gc_start_the_world()
     FSHOW_SIGNAL((stderr,"/gc_start_the_world:begin\n"));
     for(p=all_threads;p;p=p->next) {
         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 %d\n",
-                     fixnum_value(p->state));
-            }
-            FSHOW_SIGNAL((stderr, "/gc_start_the_world: resuming %lu\n",
-                          p->os_thread));
-            p->state=STATE_RUNNING;
-
-#if defined(SIG_RESUME_FROM_GC)
-            status=kill_thread_safely(p->os_thread,SIG_RESUME_FROM_GC);
-#else
-            status=kill_thread_safely(p->os_thread,SIG_STOP_FOR_GC);
-#endif
-            if (status) {
-                lose("cannot resume thread=%lu: %d, %s\n",
-                     p->os_thread,status,strerror(status));
+        if (p!=th) {
+            lispobj state = thread_state(p);
+            if (state != STATE_DEAD) {
+                if(state != STATE_SUSPENDED) {
+                    lose("gc_start_the_world: wrong thread state is %d\n",
+                         fixnum_value(state));
+                }
+                FSHOW_SIGNAL((stderr, "/gc_start_the_world: resuming %lu\n",
+                              p->os_thread));
+                set_thread_state(p, STATE_RUNNING);
             }
         }
     }
-    /* If we waited here until all threads leave STATE_SUSPENDED, then
-     * SIG_STOP_FOR_GC wouldn't need to be a rt signal. That has some
-     * performance implications, but does away with the 'rt signal
-     * queue full' problem. */
 
     lock_ret = pthread_mutex_unlock(&all_threads_lock);
     gc_assert(lock_ret == 0);
@@ -725,3 +670,13 @@ void gc_start_the_world()
     FSHOW_SIGNAL((stderr,"/gc_start_the_world:end\n"));
 }
 #endif
+
+int
+thread_yield()
+{
+#ifdef LISP_FEATURE_SB_THREAD
+    return sched_yield();
+#else
+    return 0;
+#endif
+}