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Merge branch 'rickard/proc-not-running/OTP-13365' into maint
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* rickard/proc-not-running/OTP-13365:
  Do not wait for main lock when looking up process not running
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@rickard-green
rickard-green committed Feb 24, 2016
2 parents 97ff595 + a5e6652 commit 6295f4e
Showing 1 changed file with 71 additions and 31 deletions.
102 changes: 71 additions & 31 deletions erts/emulator/beam/erl_process.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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... */
Expand Down Expand Up @@ -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;
Expand All @@ -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)
Expand Down

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