diff options
Diffstat (limited to 'libbuild2/scheduler.hxx')
| -rw-r--r-- | libbuild2/scheduler.hxx | 47 |
1 files changed, 39 insertions, 8 deletions
diff --git a/libbuild2/scheduler.hxx b/libbuild2/scheduler.hxx index 0107753..4495cb9 100644 --- a/libbuild2/scheduler.hxx +++ b/libbuild2/scheduler.hxx @@ -209,17 +209,46 @@ namespace build2 // Tune a started up scheduler. // - // Currently one cannot increase the number of max_active. Pass 0 to - // restore the initial value. + // Currently one cannot increase the number of (initial) max_active, only + // decrease it. Pass 0 to restore the initial value. Returns the old + // value (0 if it is initial). // // Note that tuning can only be done while the scheduler is inactive, that - // is, no threads are executing a task or are suspended. For example, in a + // is, no threads are executing or waiting on a task. For example, in a // setup with a single initial active thread that would be after a return - // from the top-level wait() call. + // from the top-level wait() call. Tuning the scheduler with more than one + // initial active threads is currently not supported. // - void + size_t tune (size_t max_active); + struct tune_guard + { + tune_guard (): s_ (nullptr) {} + tune_guard (scheduler& s, size_t ma): s_ (&s), o_ (s_->tune (ma)) {} + tune_guard (tune_guard&& x): s_ (x.s_), o_ (x.o_) {x.s_ = nullptr;} + tune_guard& operator= (tune_guard&& x) + { + if (&x != this) + { + s_ = x.s_; + o_ = x.o_; + x.s_ = nullptr; + } + return *this; + } + + ~tune_guard () + { + if (s_ != nullptr) + s_->tune (o_); + } + + private: + scheduler* s_; + size_t o_; + }; + // Return true if the scheduler is configured to run tasks serially. // // Note: can only be called from threads that have observed startup. @@ -415,8 +444,10 @@ namespace build2 // active <= max_active // (init_active + helpers) <= max_threads (soft; see activate_helper()) // - // Note that the first three are immutable between startup() and - // shutdown() so can be accessed without a lock (but see join()). + // Note that the first three are immutable between the startup() and + // shutdown() calls so can be accessed without a lock (but see join() and + // except for max_active_ which can be changed by tune() but only when the + // scheduler is idle). // size_t init_active_ = 0; // Initially active threads. size_t max_active_ = 0; // Maximum number of active threads. @@ -430,7 +461,7 @@ namespace build2 // size_t active_ = 0; // Active master threads executing a task. size_t idle_ = 0; // Idle helper threads waiting for a task. - size_t waiting_ = 0; // Suspended master threads waiting for their tasks. + size_t waiting_ = 0; // Suspended master threads waiting on their tasks. size_t ready_ = 0; // Ready master thread waiting to become active. size_t starting_ = 0; // Helper threads starting up. |