diff options
| -rw-r--r-- | libbuild2/module.cxx | 9 | ||||
| -rw-r--r-- | libbuild2/scheduler.cxx | 31 | ||||
| -rw-r--r-- | libbuild2/scheduler.hxx | 18 |
3 files changed, 43 insertions, 15 deletions
diff --git a/libbuild2/module.cxx b/libbuild2/module.cxx index 3f4f1d0..b7b9bbb 100644 --- a/libbuild2/module.cxx +++ b/libbuild2/module.cxx @@ -127,10 +127,11 @@ namespace build2 // Note that we can only do this if we are running serially because // otherwise we cannot guarantee the scheduler is idle (we could have // waiting threads from the outer context). This is fine for now since the - // only two tuning level we use are serial and full concurrency (turns out - // currently we don't really need this: we will always be called during - // load or match phases and we always do parallel match; but let's keep it - // in case things change). + // only two tuning level we use are serial and full concurrency. (Turns + // out currently we don't really need this: we will always be called + // during load or match phases and we always do parallel match; but let's + // keep it in case things change. Actually, we may need it, if the + // scheduler was started up in a tuned state, like in bpkg). // auto sched_tune (ctx.sched.serial () ? scheduler::tune_guard (ctx.sched, 0) diff --git a/libbuild2/scheduler.cxx b/libbuild2/scheduler.cxx index bdd703d..469ded7 100644 --- a/libbuild2/scheduler.cxx +++ b/libbuild2/scheduler.cxx @@ -362,8 +362,14 @@ namespace build2 size_t init_active, size_t max_threads, size_t queue_depth, - optional<size_t> max_stack) + optional<size_t> max_stack, + size_t orig_max_active) { + if (orig_max_active == 0) + orig_max_active = max_active; + else + assert (max_active <= orig_max_active); + // Lock the mutex to make sure our changes are visible in (other) active // threads. // @@ -375,16 +381,18 @@ namespace build2 // were asked to run serially. // if (max_threads == 0) - max_threads = (max_active == 1 ? 1 : - sizeof (void*) < 8 ? 8 : 32) * max_active; + max_threads = (orig_max_active == 1 + ? 1 + : (sizeof (void*) < 8 ? 8 : 32) * orig_max_active); assert (shutdown_ && init_active != 0 && init_active <= max_active && - max_active <= max_threads); + orig_max_active <= max_threads); active_ = init_active_ = init_active; - max_active_ = orig_max_active_ = max_active; + max_active_ = max_active; + orig_max_active_ = orig_max_active; max_threads_ = max_threads; // This value should be proportional to the amount of hardware concurrency @@ -398,7 +406,7 @@ namespace build2 // task_queue_depth_ = queue_depth != 0 ? queue_depth - : max_active * 8; + : orig_max_active_ * 8; queued_task_count_.store (0, memory_order_relaxed); @@ -421,6 +429,8 @@ namespace build2 shutdown_ = false; + // Delay thread startup if serial. + // if (max_active_ != 1) dead_thread_ = thread (deadlock_monitor, this); } @@ -429,7 +439,7 @@ namespace build2 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. + // still have the deadlock monitoring thread loitering around. // 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 @@ -451,6 +461,11 @@ namespace build2 lock l (wait_idle ()); swap (max_active_, max_active); + + // Start the deadlock thread if its startup was delayed. + // + if (max_active_ != 1 && !dead_thread_.joinable ()) + dead_thread_ = thread (deadlock_monitor, this); } return max_active == orig_max_active_ ? 0 : max_active; @@ -519,7 +534,7 @@ namespace build2 // Wait for the deadlock monitor (the only remaining thread). // - if (orig_max_active_ != 1) // See tune() for why not max_active_. + if (dead_thread_.joinable ()) { l.unlock (); dead_condv_.notify_one (); diff --git a/libbuild2/scheduler.hxx b/libbuild2/scheduler.hxx index dcde79b..76b3263 100644 --- a/libbuild2/scheduler.hxx +++ b/libbuild2/scheduler.hxx @@ -301,14 +301,25 @@ namespace build2 // If the maximum threads or task queue depth arguments are unspecified, // then appropriate defaults are used. // + // Passing non-zero orig_max_active (normally the real max active) allows + // starting up a pre-tuned scheduler. In particular, starting a pre-tuned + // to serial scheduler is relatively cheap since starting the deadlock + // detection thread is delayed until the scheduler is re-tuned. + // explicit scheduler (size_t max_active, size_t init_active = 1, size_t max_threads = 0, size_t queue_depth = 0, - optional<size_t> max_stack = nullopt) + optional<size_t> max_stack = nullopt, + size_t orig_max_active = 0) { - startup (max_active, init_active, max_threads, queue_depth, max_stack); + startup (max_active, + init_active, + max_threads, + queue_depth, + max_stack, + orig_max_active); } // Start the scheduler. @@ -318,7 +329,8 @@ namespace build2 size_t init_active = 1, size_t max_threads = 0, size_t queue_depth = 0, - optional<size_t> max_stack = nullopt); + optional<size_t> max_stack = nullopt, + size_t orig_max_active = 0); // Return true if the scheduler was started up. // |