flambda-backend: port #852 (add primitive to enable/disable tick thre…

…ad) (#2054)

otherlibs/systhreads/st_stubs.c

@@ -116,6 +116,7 @@ struct caml_thread_table {
   caml_thread_t active_thread;
   st_masterlock thread_lock;
   int tick_thread_running;
+  int tick_thread_enabled;
   st_thread_id tick_thread_id;
 };
 
@@ -145,6 +146,9 @@ static void thread_lock_release(int dom_id)
 /* Whether the "tick" thread is already running for this domain */
 #define Tick_thread_running thread_table[Caml_state->id].tick_thread_running
 
+/* Whether the "tick" thread is enabled for this domain */
+#define Tick_thread_enabled thread_table[Caml_state->id].tick_thread_enabled
+
 /* The thread identifier of the "tick" thread for this domain */
 #define Tick_thread_id thread_table[Caml_state->id].tick_thread_id
 
@@ -507,15 +511,18 @@ CAMLprim value caml_thread_initialize(value unit)
   return Val_unit;
 }
 
-CAMLprim value caml_thread_cleanup(value unit)
+static void stop_tick_thread(void)
 {
-  if (Tick_thread_running){
-    atomic_store_release(&Tick_thread_stop, 1);
-    st_thread_join(Tick_thread_id);
-    atomic_store_release(&Tick_thread_stop, 0);
-    Tick_thread_running = 0;
-  }
+  if (!Tick_thread_running) return;
+  atomic_store_release(&Tick_thread_stop, 1);
+  st_thread_join(Tick_thread_id);
+  atomic_store_release(&Tick_thread_stop, 0);
+  Tick_thread_running = 0;
+}
 
+CAMLprim value caml_thread_cleanup(value unit)
+{
+  stop_tick_thread();
   return Val_unit;
 }
 
@@ -594,6 +601,29 @@ static int create_tick_thread(void)
   return err;
 }
 
+static st_retcode start_tick_thread(void)
+{
+  if (Tick_thread_running) return 0;
+  st_retcode err = create_tick_thread();
+  if (err == 0) Tick_thread_running = 1;
+  return err;
+}
+
+CAMLprim value caml_enable_tick_thread(value v_enable)
+{
+  int enable = Long_val(v_enable) ? 1 : 0;
+
+  if (enable) {
+    st_retcode err = start_tick_thread();
+    sync_check_error(err, "caml_enable_tick_thread");
+  } else {
+    stop_tick_thread();
+  }
+
+  Tick_thread_enabled = enable;
+  return Val_unit;
+}
+
 CAMLprim value caml_thread_new(value clos)
 {
   CAMLparam1(clos);
@@ -641,10 +671,9 @@ CAMLprim value caml_thread_new(value clos)
     sync_check_error(err, "Thread.create");
   }
 
-  if (! Tick_thread_running) {
-    err = create_tick_thread();
+  if (Tick_thread_enabled) {
+    err = start_tick_thread();
     sync_check_error(err, "Thread.create");
-    Tick_thread_running = 1;
   }
   CAMLreturn(th->descr);
 }
@@ -687,10 +716,9 @@ CAMLexport int caml_c_thread_register(void)
   /* Allocate the thread descriptor on the heap */
   th->descr = caml_thread_new_descriptor(Val_unit);  /* no closure */
 
-  if (! Tick_thread_running) {
-    st_retcode err = create_tick_thread();
+  if (Tick_thread_enabled) {
+    st_retcode err = start_tick_thread();
     sync_check_error(err, "caml_register_c_thread");
-    Tick_thread_running = 1;
   }
 
   /* Release the master lock */