Fix signal order for is_process_alive

7 files changed, 255 insertions, 151 deletions

diff --git a/erts/emulator/beam/bif.c b/erts/emulator/beam/bif.c
index adea7d007e..232597c5b6 100644
--- a/erts/emulator/beam/bif.c
+++ b/erts/emulator/beam/bif.c
@@ -52,7 +52,6 @@ Export *erts_await_result;
 static Export await_exit_trap;
 static Export* flush_monitor_messages_trap = NULL;
 static Export* set_cpu_topology_trap = NULL;
-static Export* await_proc_exit_trap = NULL;
 static Export* await_port_send_result_trap = NULL;
 Export* erts_format_cpu_topology_trap = NULL;
 static Export dsend_continue_trap_export;
@@ -4654,42 +4653,6 @@ static BIF_RETTYPE bif_return_trap(BIF_ALIST_2)
     BIF_RET(res);
 }
 
-void
-erts_bif_prep_await_proc_exit_data_trap(Process *c_p, Eterm pid, Eterm ret)
-{
-    ERTS_BIF_PREP_TRAP3_NO_RET(await_proc_exit_trap, c_p, pid, am_data, ret);
-}
-
-void
-erts_bif_prep_await_proc_exit_reason_trap(Process *c_p, Eterm pid)
-{
-    ERTS_BIF_PREP_TRAP3_NO_RET(await_proc_exit_trap, c_p,
-                               pid, am_reason, am_undefined);
-}
-
-void
-erts_bif_prep_await_proc_exit_apply_trap(Process *c_p,
-					 Eterm pid,
-					 Eterm module,
-					 Eterm function,
-					 Eterm args[],
-					 int nargs)
-{
-    Eterm term;
-    Eterm *hp;
-    int i;
-    ASSERT(is_atom(module) && is_atom(function));
-
-    hp = HAlloc(c_p, 4+2*nargs);
-    term = NIL;
-    for (i = nargs-1; i >= 0; i--) {
-        term = CONS(hp, args[i], term);
-        hp += 2;
-    }
-    term = TUPLE3(hp, module, function, term);
-    ERTS_BIF_PREP_TRAP3_NO_RET(await_proc_exit_trap, c_p, pid, am_apply, term);
-}
-
 Export bif_return_trap_export;
 
 void erts_init_trap_export(Export* ep, Eterm m, Eterm f, Uint a,
@@ -4742,7 +4705,6 @@ void erts_init_bif(void)
     erts_format_cpu_topology_trap = erts_export_put(am_erlang,
 						    am_format_cpu_topology,
 						    1);
-    await_proc_exit_trap = erts_export_put(am_erlang,am_await_proc_exit,3);
     await_port_send_result_trap
 	= erts_export_put(am_erts_internal, am_await_port_send_result, 3);
     system_flag_scheduler_wall_time_trap
diff --git a/erts/emulator/beam/bif.h b/erts/emulator/beam/bif.h
index dca53686f4..a33421d762 100644
--- a/erts/emulator/beam/bif.h
+++ b/erts/emulator/beam/bif.h
@@ -437,67 +437,6 @@ do {					\
 	ERTS_BIF_EXITED((PROC));	\
 } while (0)
 
-/*
- * The ERTS_BIF_*_AWAIT_X_*_TRAP makros either exits the caller, or
- * sets up a trap to erlang:await_proc_exit/3.
- *
- * The caller is acquired to hold the 'main' lock on C_P. No other locks
- * are allowed to be held.
- */
-
-#define ERTS_BIF_PREP_AWAIT_X_DATA_TRAP(RET, C_P, PID, DATA)		\
-do {									\
-    erts_bif_prep_await_proc_exit_data_trap((C_P), (PID), (DATA));	\
-    (RET) = THE_NON_VALUE;						\
-} while (0)
-
-#define ERTS_BIF_PREP_AWAIT_X_REASON_TRAP(RET, C_P, PID)		\
-do {									\
-    erts_bif_prep_await_proc_exit_reason_trap((C_P), (PID));		\
-    (RET) = THE_NON_VALUE;						\
-} while (0)
-
-#define ERTS_BIF_PREP_AWAIT_X_APPLY_TRAP(RET, C_P, PID, M, F, A, AN)	\
-do {									\
-    erts_bif_prep_await_proc_exit_apply_trap((C_P), (PID),		\
-					     (M), (F), (A), (AN));	\
-    (RET) = THE_NON_VALUE;						\
-} while (0)
-
-#define ERTS_BIF_AWAIT_X_DATA_TRAP(C_P, PID, DATA)			\
-do {									\
-    erts_bif_prep_await_proc_exit_data_trap((C_P), (PID), (DATA));	\
-    return THE_NON_VALUE;						\
-} while (0)
-
-#define ERTS_BIF_AWAIT_X_REASON_TRAP(C_P, PID)				\
-do {									\
-    erts_bif_prep_await_proc_exit_reason_trap((C_P), (PID));		\
-    return THE_NON_VALUE;						\
-} while (0)
-
-#define ERTS_BIF_AWAIT_X_APPLY_TRAP(C_P, PID, M, F, A, AN)		\
-do {									\
-    erts_bif_prep_await_proc_exit_apply_trap((C_P), (PID),		\
-					     (M), (F), (A), (AN));	\
-    return THE_NON_VALUE;						\
-} while (0)
-
-void
-erts_bif_prep_await_proc_exit_data_trap(Process *c_p,
-					Eterm pid,
-					Eterm data);
-void
-erts_bif_prep_await_proc_exit_reason_trap(Process *c_p,
-					  Eterm pid);
-void
-erts_bif_prep_await_proc_exit_apply_trap(Process *c_p,
-					 Eterm pid,
-					 Eterm module,
-					 Eterm function,
-					 Eterm args[],
-					 int nargs);
-
 int erts_call_dirty_bif(ErtsSchedulerData *esdp, Process *c_p,
 			BeamInstr *I, Eterm *reg);
 
diff --git a/erts/emulator/beam/bif.tab b/erts/emulator/beam/bif.tab
index 93613ac2eb..687fd39d58 100644
--- a/erts/emulator/beam/bif.tab
+++ b/erts/emulator/beam/bif.tab
@@ -266,6 +266,7 @@ bif erlang:demonitor/1
 bif erlang:demonitor/2
 
 bif erlang:is_process_alive/1
+bif erts_internal:is_process_alive/2
 
 bif erlang:error/1		error_1
 bif erlang:error/2		error_2
diff --git a/erts/emulator/beam/erl_bif_info.c b/erts/emulator/beam/erl_bif_info.c
index 9a3c058e82..e94544a678 100644
--- a/erts/emulator/beam/erl_bif_info.c
+++ b/erts/emulator/beam/erl_bif_info.c
@@ -73,6 +73,9 @@ static Export *gather_msacc_res_trap;
 static Export *gather_gc_info_res_trap;
 static Export *gather_system_check_res_trap;
 
+static Export *is_process_alive_trap;
+
+
 #define DECL_AM(S) Eterm AM_ ## S = am_atom_put(#S, sizeof(#S) - 1)
 
 static char otp_version[] = ERLANG_OTP_VERSION;
@@ -3502,34 +3505,53 @@ fun_info_mfa_1(BIF_ALIST_1)
     BIF_ERROR(p, BADARG);
 }
 
+BIF_RETTYPE erts_internal_is_process_alive_2(BIF_ALIST_2)
+{
+    if (!is_internal_pid(BIF_ARG_1) || !is_internal_ordinary_ref(BIF_ARG_2))
+        BIF_ERROR(BIF_P, BADARG);
+    erts_proc_sig_send_is_alive_request(BIF_P, BIF_ARG_1, BIF_ARG_2);
+    BIF_RET(am_ok);
+}
+
 BIF_RETTYPE is_process_alive_1(BIF_ALIST_1) 
 {
-   if(is_internal_pid(BIF_ARG_1)) {
-       Process *rp;
-
-       if (BIF_ARG_1 == BIF_P->common.id)
-	   BIF_RET(am_true);
-
-       rp = erts_proc_lookup_raw(BIF_ARG_1);
-       if (!rp) {
-	   BIF_RET(am_false);
-       }
-       else {
-	   if (erts_atomic32_read_acqb(&rp->state) & ERTS_PSFLG_EXITING)
-	       ERTS_BIF_AWAIT_X_DATA_TRAP(BIF_P, BIF_ARG_1, am_false);
-	   else
-	       BIF_RET(am_true);
-       }
-   }
-   else if(is_external_pid(BIF_ARG_1)) {
-       if(external_pid_dist_entry(BIF_ARG_1) == erts_this_dist_entry)
+    if (is_internal_pid(BIF_ARG_1)) {
+        erts_aint32_t state;
+        Process *rp;
+
+        if (BIF_ARG_1 == BIF_P->common.id)
+            BIF_RET(am_true);
+
+        rp = erts_proc_lookup_raw(BIF_ARG_1);
+        if (!rp)
+            BIF_RET(am_false);
+
+        state = erts_atomic32_read_acqb(&rp->state);
+        if (state & (ERTS_PSFLG_EXITING
+                     | ERTS_PSFLG_SIG_Q
+                     | ERTS_PSFLG_SIG_IN_Q)) {
+            /*
+             * If in exiting state, trap out and send 'is alive'
+             * request and wait for it to complete termination.
+             *
+             * If process has signals enqueued, we need to
+             * send it an 'is alive' request via its signal
+             * queue in order to ensure that signal order is
+             * preserved (we may earlier have sent it an
+             * exit signal that has not been processed yet).
+             */
+            BIF_TRAP1(is_process_alive_trap, BIF_P, BIF_ARG_1);
+        }
+
+        BIF_RET(am_true);
+    }
+
+   if (is_external_pid(BIF_ARG_1)) {
+       if (external_pid_dist_entry(BIF_ARG_1) == erts_this_dist_entry)
 	   BIF_RET(am_false); /* A pid from an old incarnation of this node */
-       else
-	   BIF_ERROR(BIF_P, BADARG);
-   }
-   else {
-      BIF_ERROR(BIF_P, BADARG);
    }
+
+   BIF_ERROR(BIF_P, BADARG);
 }
 
 BIF_RETTYPE process_display_2(BIF_ALIST_2)
@@ -5008,6 +5030,10 @@ erts_bif_info_init(void)
 	= erts_export_put(am_erts_internal, am_gather_microstate_accounting_result, 2);
     gather_system_check_res_trap
 	= erts_export_put(am_erts_internal, am_gather_system_check_result, 1);
+
+    is_process_alive_trap = erts_export_put(am_erts_internal, am_is_process_alive, 1);
+
+
     process_info_init();
     os_info_init();
 }
diff --git a/erts/emulator/beam/erl_proc_sig_queue.c b/erts/emulator/beam/erl_proc_sig_queue.c
index 1b5cbb1919..489df08991 100644
--- a/erts/emulator/beam/erl_proc_sig_queue.c
+++ b/erts/emulator/beam/erl_proc_sig_queue.c
@@ -48,7 +48,7 @@
  * Note that not all signal are handled using this functionality!
  */
 
-#define ERTS_SIG_Q_OP_MAX 9
+#define ERTS_SIG_Q_OP_MAX 10
 
 #define ERTS_SIG_Q_OP_EXIT                      0
 #define ERTS_SIG_Q_OP_EXIT_LINKED               1
@@ -59,7 +59,8 @@
 #define ERTS_SIG_Q_OP_UNLINK                    6
 #define ERTS_SIG_Q_OP_GROUP_LEADER              7
 #define ERTS_SIG_Q_OP_TRACE_CHANGE_STATE        8
-#define ERTS_SIG_Q_OP_PERSISTENT_MON_MSG        ERTS_SIG_Q_OP_MAX
+#define ERTS_SIG_Q_OP_PERSISTENT_MON_MSG        9
+#define ERTS_SIG_Q_OP_IS_ALIVE                  ERTS_SIG_Q_OP_MAX
 
 #define ERTS_SIG_Q_TYPE_MAX (ERTS_MON_LNK_TYPE_MAX + 5)
 
@@ -184,6 +185,11 @@ typedef struct {
     Eterm heap[1];
 } ErtsSigGroupLeader;
 
+typedef struct {
+    Eterm message;
+    Eterm requester;
+} ErtsIsAliveRequest;
+
 static int handle_msg_tracing(Process *c_p,
                               ErtsSigRecvTracing *tracing,
                               ErtsMessage ***next_nm_sig);
@@ -548,6 +554,43 @@ proc_queue_signal(Process *c_p, Eterm pid, ErtsSignal *sig, int op)
     return res;
 }
 
+static int
+maybe_elevate_sig_handling_prio(Process *c_p, Eterm other)
+{
+    /*
+     * returns:
+     *  > 0 -> elevated prio; process alive or exiting
+     *  < 0 -> no elevation needed; process alive or exiting
+     *    0 -> process terminated (free)
+     */
+    int res;
+    Process *rp;
+    erts_aint32_t state, my_prio, other_prio;
+
+    rp = erts_proc_lookup_raw(other);
+    if (!rp)
+        res = 0;
+    else {
+        res = -1;
+        state = erts_atomic32_read_nob(&c_p->state);
+        my_prio = ERTS_PSFLGS_GET_USR_PRIO(state);
+
+        state = erts_atomic32_read_nob(&rp->state);
+        other_prio = ERTS_PSFLGS_GET_USR_PRIO(state);
+
+        if (other_prio > my_prio) {
+            /* Others prio is lower than mine; elevate it... */
+            res = !!erts_sig_prio(other, my_prio);
+            if (res) {
+                /* ensure handled if dirty executing... */
+                state = erts_atomic32_read_nob(&rp->state);
+                ensure_dirty_proc_handled(other, state, my_prio);
+            }
+        }
+    }
+    return res;
+}
+
 void
 erts_proc_sig_fetch(Process *proc)
 {
@@ -1215,33 +1258,10 @@ erts_proc_sig_send_group_leader(Process *c_p, Eterm to, Eterm gl, Eterm ref)
     if (!res)
         destroy_sig_group_leader(sgl);
     else if (c_p) {
-        int prio_res = !0;
         erts_aint_t flags, rm_flags = ERTS_SIG_GL_FLG_SENDER;
-        Process *rp;
-        erts_aint32_t state, my_prio, other_prio;
-
-        state = erts_atomic32_read_nob(&c_p->state);
-        my_prio = ERTS_PSFLGS_GET_USR_PRIO(state);
-
-        rp = erts_proc_lookup_raw(to);
-        if (!rp)
-            prio_res = 0;
-        else {
-            state = erts_atomic32_read_nob(&rp->state);
-            other_prio = ERTS_PSFLGS_GET_USR_PRIO(state);
-
-            if (other_prio > my_prio) {
-                /* Others prio is lower than mine; elevate it... */
-                prio_res = erts_sig_prio(to, my_prio);
-                if (prio_res) {
-                    state = erts_atomic32_read_nob(&rp->state);
-                    ensure_dirty_proc_handled(to, state, my_prio);
-                }
-            }
-        }
+        int prio_res = maybe_elevate_sig_handling_prio(c_p, to);
         if (!prio_res)
             rm_flags |= ERTS_SIG_GL_FLG_ACTIVE;
-
         flags = erts_atomic_read_band_nob(&sgl->flags, ~rm_flags);
         if (!prio_res && (flags & ERTS_SIG_GL_FLG_ACTIVE))
             res = 0; /* We deactivated signal... */
@@ -1253,6 +1273,99 @@ erts_proc_sig_send_group_leader(Process *c_p, Eterm to, Eterm gl, Eterm ref)
         group_leader_reply(c_p, c_p->common.id, ref, 0);
 }
 
+void
+erts_proc_sig_send_is_alive_request(Process *c_p, Eterm to, Eterm ref)
+{
+    ErlHeapFragment *hfrag;
+    Uint hsz;
+    Eterm *hp, *start_hp, ref_cpy, msg;
+    ErlOffHeap *ohp;
+    ErtsMessage *mp;
+    ErtsIsAliveRequest *alive_req;
+
+    ASSERT(is_internal_ordinary_ref(ref));
+
+    hsz = ERTS_REF_THING_SIZE + 3 + sizeof(ErtsIsAliveRequest)/sizeof(Eterm);
+
+    mp = erts_alloc_message(hsz, &hp);
+    hfrag = &mp->hfrag;
+    mp->next = NULL;
+    ohp = &hfrag->off_heap;
+    start_hp = hp;
+
+    ref_cpy = STORE_NC(&hp, ohp, ref);
+    msg = TUPLE2(hp, ref_cpy, am_false); /* default res 'false' */
+    hp += 3;
+
+    hfrag->used_size = hp - start_hp;
+
+    alive_req = (ErtsIsAliveRequest *) (char *) hp;
+    alive_req->message = msg;
+    alive_req->requester = c_p->common.id;
+
+    ERL_MESSAGE_TERM(mp) = ERTS_PROC_SIG_MAKE_TAG(ERTS_SIG_Q_OP_IS_ALIVE,
+                                                  ERTS_SIG_Q_TYPE_UNDEFINED,
+                                                  0);
+    ERL_MESSAGE_TOKEN(mp) = NIL;
+    ERL_MESSAGE_FROM(mp) = am_system;
+#ifdef USE_VM_PROBES
+    ERL_MESSAGE_DT_UTAG(mp) = NIL;
+#endif
+
+    if (proc_queue_signal(c_p, to, (ErtsSignal *) mp, ERTS_SIG_Q_OP_IS_ALIVE))
+        (void) maybe_elevate_sig_handling_prio(c_p, to);
+    else {
+        /* It wasn't alive; reply to ourselves... */
+        mp->next = NULL;
+        mp->data.attached = ERTS_MSG_COMBINED_HFRAG;
+        erts_queue_message(c_p, ERTS_PROC_LOCK_MAIN,
+                           mp, msg, am_system);
+    }
+}
+
+static void
+is_alive_response(Process *c_p, ErtsMessage *mp, int is_alive)
+{
+    /*
+     * Sender prepared the message for us. Just patch
+     * the result if necessary. The default prepared
+     * result is 'false'.
+     */
+    Process *rp;
+    ErtsIsAliveRequest *alive_req;
+
+    alive_req = (ErtsIsAliveRequest *) (char *) (&mp->hfrag.mem[0]
+                                                 + mp->hfrag.used_size);
+
+
+    ASSERT(ERTS_SIG_IS_NON_MSG(mp));
+    ASSERT(ERTS_PROC_SIG_OP(((ErtsSignal *) mp)->common.tag)
+           == ERTS_SIG_Q_OP_IS_ALIVE);
+    ASSERT(mp->hfrag.alloc_size > mp->hfrag.used_size);
+    ASSERT((mp->hfrag.alloc_size - mp->hfrag.used_size)*sizeof(UWord)
+           >= sizeof(ErtsIsAliveRequest));
+    ASSERT(is_internal_pid(alive_req->requester));
+    ASSERT(alive_req->requester != c_p->common.id);
+    ASSERT(is_tuple_arity(alive_req->message, 2));
+    ASSERT(is_internal_ordinary_ref(tuple_val(alive_req->message)[1]));
+    ASSERT(tuple_val(alive_req->message)[2] == am_false);
+
+    ERL_MESSAGE_TERM(mp) = alive_req->message;
+    mp->data.attached = ERTS_MSG_COMBINED_HFRAG;
+    mp->next = NULL;
+
+    rp = erts_proc_lookup(alive_req->requester);
+    if (!rp)
+        erts_cleanup_messages(mp);
+    else {
+        if (is_alive) { /* patch result... */
+            Eterm *tp = tuple_val(alive_req->message);
+            tp[2] = am_true;
+        }
+        erts_queue_message(rp, 0, mp, alive_req->message, am_system);
+    }
+}
+
 static ERTS_INLINE void
 adjust_tracing_state(Process *c_p, ErtsSigRecvTracing *tracing, int setup)
 {
@@ -2355,6 +2468,13 @@ erts_proc_sig_handle_incoming(Process *c_p, erts_aint32_t *statep,
             break;
         }
 
+        case ERTS_SIG_Q_OP_IS_ALIVE:
+            ERTS_PROC_SIG_HDBG_PRIV_CHKQ(c_p, &tracing, next_nm_sig);
+            remove_nm_sig(c_p, sig, next_nm_sig);
+            is_alive_response(c_p, sig, !0);
+            ERTS_PROC_SIG_HDBG_PRIV_CHKQ(c_p, &tracing, next_nm_sig);
+            break;
+
         case ERTS_SIG_Q_OP_TRACE_CHANGE_STATE: {
             Uint16 type = ERTS_PROC_SIG_TYPE(tag);
 
@@ -2667,6 +2787,12 @@ erts_proc_sig_handle_exit(Process *c_p, int *redsp)
             break;
         }
 
+        case ERTS_SIG_Q_OP_IS_ALIVE:
+            ERTS_PROC_SIG_HDBG_PRIV_CHKQ(c_p, &tracing, next_nm_sig);
+            is_alive_response(c_p, sig, 0);
+            ERTS_PROC_SIG_HDBG_PRIV_CHKQ(c_p, &tracing, next_nm_sig);
+            break;
+
         case ERTS_SIG_Q_OP_TRACE_CHANGE_STATE:
             destroy_trace_info((ErtsSigTraceInfo *) sig);
             break;
@@ -2803,6 +2929,7 @@ erts_proc_sig_signal_size(ErtsSignal *sig)
         break;
 
     case ERTS_SIG_Q_OP_PERSISTENT_MON_MSG:
+    case ERTS_SIG_Q_OP_IS_ALIVE:
         size = ((ErtsMessage *) sig)->hfrag.alloc_size;
         size *= sizeof(Eterm);
         size += sizeof(ErtsMessage) - sizeof(Eterm);
@@ -3514,6 +3641,7 @@ erts_proc_sig_debug_foreach_sig(Process *c_p,
                     break;
                 }
 
+                case ERTS_SIG_Q_OP_IS_ALIVE:
                 case ERTS_SIG_Q_OP_TRACE_CHANGE_STATE:
                     break;
 
diff --git a/erts/emulator/beam/erl_proc_sig_queue.h b/erts/emulator/beam/erl_proc_sig_queue.h
index 433e30ce4a..56fe3e683e 100644
--- a/erts/emulator/beam/erl_proc_sig_queue.h
+++ b/erts/emulator/beam/erl_proc_sig_queue.h
@@ -31,6 +31,7 @@
  *              - Link
  *              - Unlink
  *              - Group leader
+ *              - Is process alive
  *              - Trace change
  *
  *              The signal queue consists of three parts:
@@ -426,6 +427,30 @@ void
 erts_proc_sig_send_group_leader(Process *c_p, Eterm to, Eterm gl,
                                 Eterm ref);
 
+/**
+ *
+ * @brief Send an 'is process alive' signal to a process.
+ *
+ * A response message '{Ref, Result}' is sent to the
+ * sender when performed where Ref is the reference passed
+ * as 'ref' argument, and Result is either 'true' or 'false'.
+ *
+ * @param[in]     c_p           Pointer to process struct of
+ *                              currently executing process.
+ *                              NULL if signal arrived via
+ *                              distribution.
+ *
+ * @param[in]     to            Identifier of receiver.
+ *
+ * @param[in]     ref           Reference to use in response
+ *                              message to the sending
+ *                              process (i.e., c_p).
+ *
+ */
+void
+erts_proc_sig_send_is_alive_request(Process *c_p, Eterm to,
+                                    Eterm ref);
+
 /*
  * End of send operations of currently supported process signals.
  */
diff --git a/erts/emulator/test/bif_SUITE.erl b/erts/emulator/test/bif_SUITE.erl
index d16c6a320d..22706ae8b1 100644
--- a/erts/emulator/test/bif_SUITE.erl
+++ b/erts/emulator/test/bif_SUITE.erl
@@ -34,7 +34,8 @@
          erl_crash_dump_bytes/1,
 	 is_builtin/1, error_stacktrace/1,
 	 error_stacktrace_during_call_trace/1,
-         group_leader_prio/1, group_leader_prio_dirty/1]).
+         group_leader_prio/1, group_leader_prio_dirty/1,
+         is_process_alive/1]).
 
 suite() ->
     [{ct_hooks,[ts_install_cth]},
@@ -48,7 +49,8 @@ all() ->
      atom_to_binary, binary_to_atom, binary_to_existing_atom,
      erl_crash_dump_bytes, min_max, erlang_halt, is_builtin,
      error_stacktrace, error_stacktrace_during_call_trace,
-     group_leader_prio, group_leader_prio_dirty].
+     group_leader_prio, group_leader_prio_dirty,
+     is_process_alive].
 
 %% Uses erlang:display to test that erts_printf does not do deep recursion
 display(Config) when is_list(Config) ->
@@ -1076,6 +1078,27 @@ group_leader_prio_test(Dirty) ->
                   TLs),
     ok.
 
+is_process_alive(Config) when is_list(Config) ->
+    process_flag(priority, max),
+    Ps = lists:map(fun (_) ->
+                           spawn_opt(fun () -> tok_loop() end,
+                                     [{priority, high}, link])
+                   end,
+                   lists:seq(1, 2*erlang:system_info(schedulers))),
+    receive after 1000 -> ok end, %% Wait for load to spread
+    lists:foreach(fun (P) ->
+                          %% Ensure that signal order is preserved
+                          %% and that we are not starved due to
+                          %% priority inversion
+                          true = erlang:is_process_alive(P),
+                          unlink(P),
+                          true = erlang:is_process_alive(P),
+                          exit(P, kill),
+                          false = erlang:is_process_alive(P)
+                  end,
+                  Ps),
+    ok.
+
 %% helpers
     
 id(I) -> I.