create separate function to spawn GC threads (JuliaLang#55108)

Third-party GCs (e.g. MMTk) will probably have their own function to
spawn GC threads.

src/gc.c

@@ -3957,6 +3957,26 @@ void jl_free_thread_gc_state(jl_ptls_t ptls)
  arraylist_free(&mq->reclaim_set);
 }
 
+void jl_start_gc_threads(void)
+{
+ int nthreads = jl_atomic_load_relaxed(&jl_n_threads);
+ int ngcthreads = jl_n_gcthreads;
+ int nmutator_threads = nthreads - ngcthreads;
+ uv_thread_t uvtid;
+ for (int i = nmutator_threads; i < nthreads; ++i) {
+ jl_threadarg_t *t = (jl_threadarg_t *)malloc_s(sizeof(jl_threadarg_t)); // ownership will be passed to the thread
+ t->tid = i;
+ t->barrier = &thread_init_done;
+ if (i == nthreads - 1 && jl_n_sweepthreads == 1) {
+ uv_thread_create(&uvtid, jl_concurrent_gc_threadfun, t);
+ }
+ else {
+ uv_thread_create(&uvtid, jl_parallel_gc_threadfun, t);
+ }
+ uv_thread_detach(&uvtid);
+ }
+}
+
 // System-wide initializations
 void jl_gc_init(void)
 {

src/gc.h

@@ -572,6 +572,7 @@ extern uv_cond_t gc_threads_cond;
 extern uv_sem_t gc_sweep_assists_needed;
 extern _Atomic(int) gc_n_threads_marking;
 extern _Atomic(int) gc_n_threads_sweeping;
+extern uv_barrier_t thread_init_done;
 void gc_mark_queue_all_roots(jl_ptls_t ptls, jl_gc_markqueue_t *mq);
 void gc_mark_finlist_(jl_gc_markqueue_t *mq, jl_value_t *fl_parent, jl_value_t **fl_begin, jl_value_t **fl_end) JL_NOTSAFEPOINT;
 void gc_mark_finlist(jl_gc_markqueue_t *mq, arraylist_t *list, size_t start) JL_NOTSAFEPOINT;

src/init.c

@@ -885,6 +885,8 @@ static NOINLINE void _finish_julia_init(JL_IMAGE_SEARCH rel, jl_ptls_t ptls, jl_
  post_image_load_hooks();
  }
  jl_start_threads();
+ jl_start_gc_threads();
+ uv_barrier_wait(&thread_init_done);
 
  jl_gc_enable(1);
 

src/julia_internal.h

@@ -960,9 +960,10 @@ extern JL_DLLEXPORT ssize_t jl_tls_offset;
 extern JL_DLLEXPORT const int jl_tls_elf_support;
 void jl_init_threading(void);
 void jl_start_threads(void);
-extern uv_mutex_t safepoint_lock;
+void jl_start_gc_threads(void);
 
 // Whether the GC is running
+extern uv_mutex_t safepoint_lock;
 extern char *jl_safepoint_pages;
 STATIC_INLINE int jl_addr_is_safepoint(uintptr_t addr)
 {

src/threading.c

@@ -761,7 +761,7 @@ void jl_init_threading(void)
  gc_first_tid = nthreads + nthreadsi;
 }
 
-static uv_barrier_t thread_init_done;
+uv_barrier_t thread_init_done;
 
 void jl_start_threads(void)
 {
@@ -800,30 +800,20 @@ void jl_start_threads(void)
  uv_barrier_init(&thread_init_done, nthreads);
 
  // GC/System threads need to be after the worker threads.
- int nworker_threads = nthreads - ngcthreads;
+ int nmutator_threads = nthreads - ngcthreads;
 
- for (i = 1; i < nthreads; ++i) {
+ for (i = 1; i < nmutator_threads; ++i) {
  jl_threadarg_t *t = (jl_threadarg_t *)malloc_s(sizeof(jl_threadarg_t)); // ownership will be passed to the thread
  t->tid = i;
  t->barrier = &thread_init_done;
- if (i < nworker_threads) {
- uv_thread_create(&uvtid, jl_threadfun, t);
- if (exclusive) {
- mask[i] = 1;
- uv_thread_setaffinity(&uvtid, mask, NULL, cpumasksize);
- mask[i] = 0;
- }
- }
- else if (i == nthreads - 1 && jl_n_sweepthreads == 1) {
- uv_thread_create(&uvtid, jl_concurrent_gc_threadfun, t);
- }
- else {
- uv_thread_create(&uvtid, jl_parallel_gc_threadfun, t);
+ uv_thread_create(&uvtid, jl_threadfun, t);
+ if (exclusive) {
+ mask[i] = 1;
+ uv_thread_setaffinity(&uvtid, mask, NULL, cpumasksize);
+ mask[i] = 0;
  }
  uv_thread_detach(&uvtid);
  }
-
- uv_barrier_wait(&thread_init_done);
 }
 
 _Atomic(unsigned) _threadedregion; // keep track of whether to prioritize IO or threading

src/threading.h

@@ -12,6 +12,8 @@ extern "C" {
 
 #define PROFILE_JL_THREADING 0
 
+extern uv_barrier_t thread_init_done;
+
 extern _Atomic(jl_ptls_t*) jl_all_tls_states JL_GLOBALLY_ROOTED; /* thread local storage */
 
 typedef struct _jl_threadarg_t {