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authorRickard Green <[email protected]>2016-02-23 18:31:52 +0100
committerRickard Green <[email protected]>2016-02-23 20:07:08 +0100
commita5e66520d92d283d14f1352dcfd0ce889c27a0c5 (patch)
tree19f64093f0a090ffdbdbad58573545c453f50b18
parent739a8f167d8adbb85f3c116c8c3bb20263f15349 (diff)
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Do not wait for main lock when looking up process not running
-rw-r--r--erts/emulator/beam/erl_process.c102
1 files changed, 71 insertions, 31 deletions
diff --git a/erts/emulator/beam/erl_process.c b/erts/emulator/beam/erl_process.c
index b24f26138c..adea745471 100644
--- a/erts/emulator/beam/erl_process.c
+++ b/erts/emulator/beam/erl_process.c
@@ -6462,9 +6462,6 @@ suspend_process(Process *c_p, Process *p)
if (suspended) {
- ASSERT(!(ERTS_PSFLG_RUNNING & state)
- || p == erts_get_current_process());
-
if (suspended > 0 && erts_system_profile_flags.runnable_procs) {
/* 'state' is before our change... */
@@ -8411,9 +8408,8 @@ pid2proc_not_running(Process *c_p, ErtsProcLocks c_p_locks,
resume_process(rp, rp_locks);
}
else {
-
rp = erts_pid2proc(c_p, c_p_locks|ERTS_PROC_LOCK_STATUS,
- pid, pid_locks|ERTS_PROC_LOCK_STATUS);
+ pid, ERTS_PROC_LOCK_STATUS);
if (!rp) {
c_p->flags &= ~F_P2PNR_RESCHED;
@@ -8422,40 +8418,84 @@ pid2proc_not_running(Process *c_p, ErtsProcLocks c_p_locks,
ASSERT(!(c_p->flags & F_P2PNR_RESCHED));
- if (suspend) {
- if (suspend_process(c_p, rp))
- goto done;
- }
- else {
- if (!((ERTS_PSFLG_RUNNING|ERTS_PSFLG_RUNNING_SYS)
- & erts_smp_atomic32_read_acqb(&rp->state)))
- goto done;
+ /*
+ * Suspend the other process in order to prevent
+ * it from being selected for normal execution.
+ * This will however not prevent it from being
+ * selected for execution of a system task. If
+ * it is selected for execution of a system task
+ * we might be blocked for quite a while if the
+ * try-lock below fails. That is, there is room
+ * for improvement here...
+ */
- }
+ if (!suspend_process(c_p, rp)) {
+ /* Other process running */
- /* Other process running */
+ ASSERT(ERTS_PSFLG_RUNNING
+ & erts_smp_atomic32_read_nob(&rp->state));
- /*
- * If we got pending suspenders and suspend ourselves waiting
- * to suspend another process we might deadlock.
- * In this case we have to yield, be suspended by
- * someone else and then do it all over again.
- */
- if (!c_p->pending_suspenders) {
- /* Mark rp pending for suspend by c_p */
- add_pend_suspend(rp, c_p->common.id, handle_pend_sync_suspend);
- ASSERT(is_nil(c_p->suspendee));
+ running:
- /* Suspend c_p; when rp is suspended c_p will be resumed. */
- suspend_process(c_p, c_p);
- c_p->flags |= F_P2PNR_RESCHED;
+ /*
+ * If we got pending suspenders and suspend ourselves waiting
+ * to suspend another process we might deadlock.
+ * In this case we have to yield, be suspended by
+ * someone else and then do it all over again.
+ */
+ if (!c_p->pending_suspenders) {
+ /* Mark rp pending for suspend by c_p */
+ add_pend_suspend(rp, c_p->common.id, handle_pend_sync_suspend);
+ ASSERT(is_nil(c_p->suspendee));
+
+ /* Suspend c_p; when rp is suspended c_p will be resumed. */
+ suspend_process(c_p, c_p);
+ c_p->flags |= F_P2PNR_RESCHED;
+ }
+ /* Yield (caller is assumed to yield immediately in bif). */
+ erts_smp_proc_unlock(rp, ERTS_PROC_LOCK_STATUS);
+ rp = ERTS_PROC_LOCK_BUSY;
+ }
+ else {
+ ErtsProcLocks need_locks = pid_locks & ~ERTS_PROC_LOCK_STATUS;
+ if (need_locks && erts_smp_proc_trylock(rp, need_locks) == EBUSY) {
+ if (ERTS_PSFLG_RUNNING_SYS
+ & erts_smp_atomic32_read_nob(&rp->state)) {
+ /* Executing system task... */
+ resume_process(rp, ERTS_PROC_LOCK_STATUS);
+ goto running;
+ }
+ erts_smp_proc_unlock(rp, ERTS_PROC_LOCK_STATUS);
+ /*
+ * If we are unlucky, the process just got selected for
+ * execution of a system task. In this case we may be
+ * blocked here for quite a while... Execution of system
+ * tasks are fortunately quite rare events. We try to
+ * avoid this by checking if it is in a state executing
+ * system tasks (above), but it will not prevent all
+ * scenarios for a long block here...
+ */
+ rp = erts_pid2proc(c_p, c_p_locks|ERTS_PROC_LOCK_STATUS,
+ pid, pid_locks|ERTS_PROC_LOCK_STATUS);
+ if (!rp)
+ goto done;
+ }
+
+ /*
+ * The previous suspend has prevented the process
+ * from being selected for normal execution regardless
+ * of locks held or not held on it...
+ */
+ ASSERT(!(ERTS_PSFLG_RUNNING
+ & erts_smp_atomic32_read_nob(&rp->state)));
+
+ if (!suspend)
+ resume_process(rp, pid_locks|ERTS_PROC_LOCK_STATUS);
}
- /* Yield (caller is assumed to yield immediately in bif). */
- erts_smp_proc_unlock(rp, pid_locks|ERTS_PROC_LOCK_STATUS);
- rp = ERTS_PROC_LOCK_BUSY;
}
done:
+
if (rp && rp != ERTS_PROC_LOCK_BUSY && !(pid_locks & ERTS_PROC_LOCK_STATUS))
erts_smp_proc_unlock(rp, ERTS_PROC_LOCK_STATUS);
if (unlock_c_p_status)