Distinguish between GC disabled by BIFs and other disabled GC

Processes remember heap fragments that are known to be fully
live due to creation in a just called BIF that yields in the
live_hf_end field. This field must not be used if we have not
disabled GC in a BIF. F_DELAY_GC has been introduced in order
to distinguish between to two different scenarios.

- F_DISABLE_GC should *only* be used by BIFs. This when
  the BIF needs to yield while preventig a GC.
- F_DELAY_GC should only be used when GC is temporarily
  disabled while the process is scheduled. A process must
  not be scheduled out while F_DELAY_GC is set.

4 files changed, 34 insertions, 11 deletions

diff --git a/erts/emulator/beam/beam_emu.c b/erts/emulator/beam/beam_emu.c
index 208a16dfd0..95a22e6c54 100644
--- a/erts/emulator/beam/beam_emu.c
+++ b/erts/emulator/beam/beam_emu.c
@@ -1843,8 +1843,8 @@ void process_main(void)
       * in the queue. This since messages with data outside
       * the heap will be corrupted by a GC.
       */
-     ASSERT(!(c_p->flags & F_DISABLE_GC));
-     c_p->flags |= F_DISABLE_GC;
+     ASSERT(!(c_p->flags & F_DELAY_GC));
+     c_p->flags |= F_DELAY_GC;
 
  loop_rec__:
      PROCESS_MAIN_CHK_LOCKS(c_p);
@@ -1858,7 +1858,7 @@ void process_main(void)
 	 if (ERTS_PROC_PENDING_EXIT(c_p)) {
 	     erts_smp_proc_unlock(c_p, ERTS_PROC_LOCKS_MSG_RECEIVE);
 	     SWAPOUT;
-	     c_p->flags &= ~F_DISABLE_GC;
+	     c_p->flags &= ~F_DELAY_GC;
 	     goto do_schedule; /* Will be rescheduled for exit */
 	 }
 	 ERTS_SMP_MSGQ_MV_INQ2PRIVQ(c_p);
@@ -1868,7 +1868,7 @@ void process_main(void)
 	 else
 #endif
 	 {
-	     c_p->flags &= ~F_DISABLE_GC;
+	     c_p->flags &= ~F_DELAY_GC;
 	     SET_I((BeamInstr *) Arg(0));
 	     Goto(*I);		/* Jump to a wait or wait_timeout instruction */
 	 }
@@ -1997,7 +1997,7 @@ void process_main(void)
      CANCEL_TIMER(c_p);
 
      erts_save_message_in_proc(c_p, msgp);
-     c_p->flags &= ~F_DISABLE_GC;
+     c_p->flags &= ~F_DELAY_GC;
 
      if (ERTS_IS_GC_DESIRED_INTERNAL(c_p, HTOP, E)) {
 	 /*
@@ -2019,7 +2019,7 @@ void process_main(void)
      */
  OpCase(loop_rec_end_f): {
 
-     ASSERT(c_p->flags & F_DISABLE_GC);
+     ASSERT(c_p->flags & F_DELAY_GC);
 
      SET_I((BeamInstr *) Arg(0));
      SAVE_MESSAGE(c_p);
@@ -2028,7 +2028,7 @@ void process_main(void)
 	 goto loop_rec__;
      }
 
-     c_p->flags &= ~F_DISABLE_GC;
+     c_p->flags &= ~F_DELAY_GC;
      c_p->i = I;
      SWAPOUT;
      c_p->arity = 0;
diff --git a/erts/emulator/beam/erl_gc.c b/erts/emulator/beam/erl_gc.c
index 3bb1f601aa..3784367195 100644
--- a/erts/emulator/beam/erl_gc.c
+++ b/erts/emulator/beam/erl_gc.c
@@ -440,8 +440,15 @@ delay_garbage_collection(Process *p, ErlHeapFragment *live_hf_end, int need)
 
     ERTS_HOLE_CHECK(p);
 
-    if (p->live_hf_end == ERTS_INVALID_HFRAG_PTR)
+    if ((p->flags & F_DISABLE_GC)
+	&& p->live_hf_end == ERTS_INVALID_HFRAG_PTR) {
+	/*
+	 * A BIF yielded with disabled GC. Remember
+	 * heap fragments created by the BIF until we
+	 * do next GC.
+	 */
 	p->live_hf_end = live_hf_end;
+    }
 
     if (need == 0)
 	return 1;
@@ -564,10 +571,12 @@ garbage_collect(Process* p, ErlHeapFragment *live_hf_end,
     DTRACE_CHARBUF(pidbuf, DTRACE_TERM_BUF_SIZE);
 #endif
 
-    if (p->flags & F_DISABLE_GC)
+    if (p->flags & (F_DISABLE_GC|F_DELAY_GC))
 	return delay_garbage_collection(p, live_hf_end, need);
 
-    if (p->live_hf_end != ERTS_INVALID_HFRAG_PTR)
+    if (p->abandoned_heap)
+	live_hf_end = ERTS_INVALID_HFRAG_PTR;
+    else if (p->live_hf_end != ERTS_INVALID_HFRAG_PTR)
 	live_hf_end = p->live_hf_end;
 
     esdp = erts_get_scheduler_data();
diff --git a/erts/emulator/beam/erl_process.c b/erts/emulator/beam/erl_process.c
index ebe9361b8d..d17355207b 100644
--- a/erts/emulator/beam/erl_process.c
+++ b/erts/emulator/beam/erl_process.c
@@ -9262,6 +9262,8 @@ Process *schedule(Process *p, int calls)
     } else {
     sched_out_proc:
 
+	ASSERT(!(p->flags & F_DELAY_GC));
+
 #ifdef ERTS_SMP
 	ERTS_SMP_CHK_HAVE_ONLY_MAIN_PROC_LOCK(p);
 	esdp = p->scheduler_data;
diff --git a/erts/emulator/beam/erl_process.h b/erts/emulator/beam/erl_process.h
index b80aa12872..41b367435d 100644
--- a/erts/emulator/beam/erl_process.h
+++ b/erts/emulator/beam/erl_process.h
@@ -1288,10 +1288,22 @@ extern struct erts_system_profile_flags_t erts_system_profile_flags;
 #define F_HAVE_BLCKD_MSCHED  (1 <<  8) /* Process has blocked multi-scheduling */
 #define F_P2PNR_RESCHED      (1 <<  9) /* Process has been rescheduled via erts_pid2proc_not_running() */
 #define F_FORCE_GC           (1 << 10) /* Force gc at process in-scheduling */
-#define F_DISABLE_GC         (1 << 11) /* Disable GC */
+#define F_DISABLE_GC         (1 << 11) /* Disable GC (see below) */
 #define F_OFF_HEAP_MSGQ      (1 << 12) /* Off heap msg queue */
 #define F_OFF_HEAP_MSGQ_CHNG (1 << 13) /* Off heap msg queue changing */
 #define F_ABANDONED_HEAP_USE (1 << 14) /* Have usage of abandoned heap */
+#define F_DELAY_GC           (1 << 15) /* Similar to disable GC (see below) */
+
+/*
+ * F_DISABLE_GC and F_DELAY_GC are similar. Both will prevent
+ * GC of the process, but it is important to use the right
+ * one:
+ * - F_DISABLE_GC should *only* be used by BIFs. This when
+ *   the BIF needs to yield while preventig a GC.
+ * - F_DELAY_GC should only be used when GC is temporarily
+ *   disabled while the process is scheduled. A process must
+ *   not be scheduled out while F_DELAY_GC is set.
+ */
 
 /* process trace_flags */
 #define F_SENSITIVE          (1 << 0)