Merge commit '1531d6e543' as 'gitstatus'

gitstatus/src/thread_pool.h

@@ -0,0 +1,74 @@
+#ifndef ROMKATV_GITSTATUS_THREAD_POOL_H_
+#define ROMKATV_GITSTATUS_THREAD_POOL_H_
+
+#include <condition_variable>
+#include <cstddef>
+#include <cstdint>
+#include <functional>
+#include <mutex>
+#include <queue>
+#include <thread>
+#include <tuple>
+#include <utility>
+
+#include "time.h"
+
+namespace gitstatus {
+
+class ThreadPool {
+ public:
+  explicit ThreadPool(size_t num_threads);
+  ThreadPool(ThreadPool&&) = delete;
+
+  // Waits for the currently running functions to finish.
+  // Does NOT wait for the queue of functions to drain.
+  // If you want the latter, call Wait() manually.
+  ~ThreadPool();
+
+  // Runs `f` on one of the threads at or after time `t`. Can be called
+  // from any thread. Can be called concurrently.
+  //
+  // Does not block.
+  void Schedule(Time t, std::function<void()> f);
+
+  void Schedule(std::function<void()> f) { Schedule(Clock::now(), std::move(f)); }
+
+  // Blocks until the work queue is empty and there are no currently
+  // running functions.
+  void Wait();
+
+  size_t num_threads() const { return threads_.size(); }
+
+ private:
+  struct Work {
+    bool operator<(const Work& w) const { return std::tie(w.t, w.idx) < std::tie(t, idx); }
+    Time t;
+    int64_t idx;
+    mutable std::function<void()> f;
+  };
+
+  void Loop(size_t tid);
+
+  int64_t last_idx_ = 0;
+  int64_t num_inflight_;
+  bool exit_ = false;
+  // Do we have a thread waiting on sleeper_cv_?
+  bool have_sleeper_ = false;
+  std::mutex mutex_;
+  // Any number of threads can wait on this condvar. Always without a timeout.
+  std::condition_variable cv_;
+  // At most one thread can wait on this condvar at a time. Always with a timeout.
+  std::condition_variable sleeper_cv_;
+  // Signalled when the work queue is empty and there is nothing inflight.
+  std::condition_variable idle_cv_;
+  std::priority_queue<Work> work_;
+  std::vector<std::thread> threads_;
+};
+
+void InitGlobalThreadPool(size_t num_threads);
+
+ThreadPool* GlobalThreadPool();
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_THREAD_POOL_H_