CScheduler class for lightweight task scheduling

Simple class to manage a task queue that is serviced by one or
more threads.

src/Makefile.am

@@ -115,6 +115,7 @@ BITCOIN_CORE_H = \
   rpcclient.h \
   rpcprotocol.h \
   rpcserver.h \
+  scheduler.h \
   script/interpreter.h \
   script/script_error.h \
   script/script.h \
@@ -257,6 +258,7 @@ libbitcoin_common_a_SOURCES = \
   netbase.cpp \
   protocol.cpp \
   pubkey.cpp \
+  scheduler.cpp \
   script/interpreter.cpp \
   script/script.cpp \
   script/sign.cpp \

src/scheduler.cpp

@@ -0,0 +1,102 @@
+// Copyright (c) 2015 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "scheduler.h"
+
+#include <assert.h>
+#include <boost/bind.hpp>
+#include <utility>
+
+CScheduler::CScheduler() : nThreadsServicingQueue(0)
+{
+}
+
+CScheduler::~CScheduler()
+{
+    assert(nThreadsServicingQueue == 0);
+}
+
+
+#if BOOST_VERSION < 105000
+static boost::system_time toPosixTime(const boost::chrono::system_clock::time_point& t)
+{
+    boost::chrono::system_clock::duration d = t.time_since_epoch();
+    boost::chrono::microseconds usecs = boost::chrono::duration_cast<boost::chrono::microseconds>(d);
+    boost::system_time result = boost::posix_time::from_time_t(0) +
+                                boost::posix_time::microseconds(usecs.count());
+    return result;
+}
+#endif
+
+void CScheduler::serviceQueue()
+{
+    boost::unique_lock<boost::mutex> lock(newTaskMutex);
+    ++nThreadsServicingQueue;
+
+    // newTaskMutex is locked throughout this loop EXCEPT
+    // when the thread is waiting or when the user's function
+    // is called.
+    while (1) {
+        try {
+            while (taskQueue.empty()) {
+                // Wait until there is something to do.
+                newTaskScheduled.wait(lock);
+            }
+// Wait until either there is a new task, or until
+// the time of the first item on the queue:
+
+// wait_until needs boost 1.50 or later; older versions have timed_wait:
+#if BOOST_VERSION < 105000
+            while (!taskQueue.empty() && newTaskScheduled.timed_wait(lock, toPosixTime(taskQueue.begin()->first))) {
+                // Keep waiting until timeout
+            }
+#else
+            while (!taskQueue.empty() && newTaskScheduled.wait_until(lock, taskQueue.begin()->first) != boost::cv_status::timeout) {
+                // Keep waiting until timeout
+            }
+#endif
+            // If there are multiple threads, the queue can empty while we're waiting (another
+            // thread may service the task we were waiting on).
+            if (taskQueue.empty())
+                continue;
+
+            Function f = taskQueue.begin()->second;
+            taskQueue.erase(taskQueue.begin());
+
+            // Unlock before calling f, so it can reschedule itself or another task
+            // without deadlocking:
+            lock.unlock();
+            f();
+            lock.lock();
+        } catch (...) {
+            --nThreadsServicingQueue;
+            throw;
+        }
+    }
+}
+
+void CScheduler::schedule(CScheduler::Function f, boost::chrono::system_clock::time_point t)
+{
+    {
+        boost::unique_lock<boost::mutex> lock(newTaskMutex);
+        taskQueue.insert(std::make_pair(t, f));
+    }
+    newTaskScheduled.notify_one();
+}
+
+void CScheduler::scheduleFromNow(CScheduler::Function f, int64_t deltaSeconds)
+{
+    schedule(f, boost::chrono::system_clock::now() + boost::chrono::seconds(deltaSeconds));
+}
+
+static void Repeat(CScheduler* s, CScheduler::Function f, int64_t deltaSeconds)
+{
+    f();
+    s->scheduleFromNow(boost::bind(&Repeat, s, f, deltaSeconds), deltaSeconds);
+}
+
+void CScheduler::scheduleEvery(CScheduler::Function f, int64_t deltaSeconds)
+{
+    scheduleFromNow(boost::bind(&Repeat, this, f, deltaSeconds), deltaSeconds);
+}

src/scheduler.h

@@ -0,0 +1,70 @@
+// Copyright (c) 2015 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_SCHEDULER_H
+#define BITCOIN_SCHEDULER_H
+
+//
+// NOTE:
+// boost::thread / boost::function / boost::chrono should be ported to
+// std::thread / std::function / std::chrono when we support C++11.
+//
+#include <boost/function.hpp>
+#include <boost/chrono/chrono.hpp>
+#include <boost/thread.hpp>
+#include <map>
+
+//
+// Simple class for background tasks that should be run
+// periodically or once "after a while"
+//
+// Usage:
+//
+// CScheduler* s = new CScheduler();
+// s->scheduleFromNow(doSomething, 11); // Assuming a: void doSomething() { }
+// s->scheduleFromNow(boost::bind(Class::func, this, argument), 3);
+// boost::thread* t = new boost::thread(boost::bind(CScheduler::serviceQueue, s));
+//
+// ... then at program shutdown, clean up the thread running serviceQueue:
+// t->interrupt();
+// t->join();
+// delete t;
+// delete s; // Must be done after thread is interrupted/joined.
+//
+
+class CScheduler
+{
+public:
+    CScheduler();
+    ~CScheduler();
+
+    typedef boost::function<void(void)> Function;
+
+    // Call func at/after time t
+    void schedule(Function f, boost::chrono::system_clock::time_point t);
+
+    // Convenience method: call f once deltaSeconds from now
+    void scheduleFromNow(Function f, int64_t deltaSeconds);
+
+    // Another convenience method: call f approximately
+    // every deltaSeconds forever, starting deltaSeconds from now.
+    // To be more precise: every time f is finished, it
+    // is rescheduled to run deltaSeconds later. If you
+    // need more accurate scheduling, don't use this method.
+    void scheduleEvery(Function f, int64_t deltaSeconds);
+
+    // To keep things as simple as possible, there is no unschedule.
+
+    // Services the queue 'forever'. Should be run in a thread,
+    // and interrupted using boost::interrupt_thread
+    void serviceQueue();
+
+private:
+    std::multimap<boost::chrono::system_clock::time_point, Function> taskQueue;
+    boost::condition_variable newTaskScheduled;
+    boost::mutex newTaskMutex;
+    int nThreadsServicingQueue;
+};
+
+#endif