Teach the call_time trace to notice when the trace dies (non-SMP system)

The call_time trace is a special kind of tracing that requires
a tracer process just like ordinary call trace, but it never
actually sends anything to the tracer. It merely use the existence
of a trace process (and call trace flags) as an indication that
call_time tracing is active for the process.

If the tracer dies in a non-SMP run-time system, processes with
call_time tracing would not notice that the tracer had
died. Furthermore, if the set_on_spawn flag was active, the dead
tracer could be propagaged to newly spawned processes.

Before accumulating trace information in a non-SMP system, always
validate the tracer process. (In an SMP system, a reference to a
dead tracer will be cleared away each time a process is scheduled.)

While we could put all of the new code beam_bp.c, we have chosen to
make a function call from beam_bp.c to a function in erl_trace.c for
clarity's sake and to ease further maintenance. In the future, we
might want to handle tracing in more similar ways in the SMP and
non-SMP system.

1 files changed, 19 insertions, 0 deletions

diff --git a/erts/emulator/beam/erl_trace.c b/erts/emulator/beam/erl_trace.c
index 6978a5f11a..305058ceff 100644
--- a/erts/emulator/beam/erl_trace.c
+++ b/erts/emulator/beam/erl_trace.c
@@ -151,6 +151,11 @@ do { \
     message dispatcher thread takes care of that). */
 #define ERTS_GET_TRACER_REF(RES, TPID, TRACEE_FLGS) \
 do { (RES) = (TPID); } while(0)
+int
+erts_is_tracer_proc_valid(Process* p)
+{
+    return 1;
+}
 #else
 #define ERTS_NULL_TRACER_REF NULL
 #define ERTS_TRACER_REF_TYPE Process *
@@ -163,6 +168,20 @@ do { \
 	return; \
     } \
 } while (0)
+int
+erts_is_tracer_proc_valid(Process* p)
+{
+    Process* tracer;
+
+    tracer = erts_proc_lookup(ERTS_TRACER_PROC(p));
+    if (tracer && ERTS_TRACE_FLAGS(tracer) & F_TRACER) {
+	return 1;
+    } else {
+	ERTS_TRACER_PROC(p) = NIL;
+	ERTS_TRACE_FLAGS(p) = ~TRACEE_FLAGS;
+	return 0;
+    }
+}
 #endif
 
 static Uint active_sched;