From 6d700e3601a3469981995fd364d1a1ff7f158e5e Mon Sep 17 00:00:00 2001 From: Boris Kolpackov Date: Wed, 23 Oct 2019 12:21:08 +0200 Subject: Un-tune scheduler when building build system modules --- libbuild2/scheduler.cxx | 29 ++++++++++++++++++++--------- 1 file changed, 20 insertions(+), 9 deletions(-) (limited to 'libbuild2/scheduler.cxx') diff --git a/libbuild2/scheduler.cxx b/libbuild2/scheduler.cxx index 3c06176..bd2694c 100644 --- a/libbuild2/scheduler.cxx +++ b/libbuild2/scheduler.cxx @@ -125,7 +125,7 @@ namespace build2 else if (active_ == 0 && external_ == 0) { // Note that we tried to handle this directly in this thread but that - // wouldn't work for the phase lock case where we cal; deactivate and + // wouldn't work for the phase lock case where we call deactivate and // then go wait on a condition variable: we would be doing deadlock // detection while holding the lock that prevents other threads from // making progress! So it has to be a separate monitoring thread. @@ -391,24 +391,35 @@ namespace build2 dead_thread_ = thread (deadlock_monitor, this); } - void scheduler:: + size_t scheduler:: tune (size_t max_active) { // Note that if we tune a parallel scheduler to run serially, we will // still have the deadlock monitoring thread running. + // With multiple initial active threads we will need to make changes to + // max_active_ visible to other threads and which we currently say can be + // accessed between startup and shutdown without a lock. + // + assert (init_active_ == 1); + if (max_active == 0) max_active = orig_max_active_; - assert (max_active >= init_active_ && - max_active <= orig_max_active_); + if (max_active != max_active_) + { + assert (max_active >= init_active_ && + max_active <= orig_max_active_); + + // The scheduler must not be active though some threads might still be + // comming off from finishing a task. So we busy-wait for them. + // + lock l (wait_idle ()); - // The scheduler must not be active though some threads might still be - // comming off from finishing a task. So we busy-wait for them. - // - lock l (wait_idle ()); + swap (max_active_, max_active); + } - max_active_ = max_active; + return max_active == orig_max_active_ ? 0 : max_active; } auto scheduler:: -- cgit v1.1