Merge bitcoin/bitcoin#25100: Switch scheduler to steady_clock

fa90516 Switch scheduler to steady_clock (MacroFake)

Pull request description:

  There is already `mockscheduler`, so it seems brittle, confusing and redundant to be able to mock the scheduler by adjusting the system clock.

ACKs for top commit:
  laanwj:
    Code review ACK fa90516
  w0xlt:
    crACK bitcoin/bitcoin@fa90516

Tree-SHA512: 60e99065ffb881a9fb25a346d311d99424fbc72a3b636c94b5f5c17ed6373c40f358a9b27825c518d12968c033e6cfd3c62d2b62cacdddc44a0b5b74f6c1a7ae

Author: MacroFake

src/scheduler.cpp

@@ -4,11 +4,11 @@
 
 #include <scheduler.h>
 
-#include <random.h>
+#include <sync.h>
 #include <util/syscall_sandbox.h>
 #include <util/time.h>
 
-#include <assert.h>
+#include <cassert>
 #include <functional>
 #include <utility>
 
@@ -43,7 +43,7 @@ void CScheduler::serviceQueue()
             // the time of the first item on the queue:
 
             while (!shouldStop() && !taskQueue.empty()) {
-                std::chrono::system_clock::time_point timeToWaitFor = taskQueue.begin()->first;
+                std::chrono::steady_clock::time_point timeToWaitFor = taskQueue.begin()->first;
                 if (newTaskScheduled.wait_until(lock, timeToWaitFor) == std::cv_status::timeout) {
                     break; // Exit loop after timeout, it means we reached the time of the event
                 }
@@ -72,7 +72,7 @@ void CScheduler::serviceQueue()
     newTaskScheduled.notify_one();
 }
 
-void CScheduler::schedule(CScheduler::Function f, std::chrono::system_clock::time_point t)
+void CScheduler::schedule(CScheduler::Function f, std::chrono::steady_clock::time_point t)
 {
     {
         LOCK(newTaskMutex);
@@ -89,7 +89,7 @@ void CScheduler::MockForward(std::chrono::seconds delta_seconds)
         LOCK(newTaskMutex);
 
         // use temp_queue to maintain updated schedule
-        std::multimap<std::chrono::system_clock::time_point, Function> temp_queue;
+        std::multimap<std::chrono::steady_clock::time_point, Function> temp_queue;
 
         for (const auto& element : taskQueue) {
             temp_queue.emplace_hint(temp_queue.cend(), element.first - delta_seconds, element.second);
@@ -114,8 +114,8 @@ void CScheduler::scheduleEvery(CScheduler::Function f, std::chrono::milliseconds
     scheduleFromNow([this, f, delta] { Repeat(*this, f, delta); }, delta);
 }
 
-size_t CScheduler::getQueueInfo(std::chrono::system_clock::time_point& first,
-                                std::chrono::system_clock::time_point& last) const
+size_t CScheduler::getQueueInfo(std::chrono::steady_clock::time_point& first,
+                                std::chrono::steady_clock::time_point& last) const
 {
     LOCK(newTaskMutex);
     size_t result = taskQueue.size();
@@ -143,7 +143,7 @@ void SingleThreadedSchedulerClient::MaybeScheduleProcessQueue()
         if (m_are_callbacks_running) return;
         if (m_callbacks_pending.empty()) return;
     }
-    m_scheduler.schedule([this] { this->ProcessQueue(); }, std::chrono::system_clock::now());
+    m_scheduler.schedule([this] { this->ProcessQueue(); }, std::chrono::steady_clock::now());
 }
 
 void SingleThreadedSchedulerClient::ProcessQueue()

src/scheduler.h

@@ -46,12 +46,12 @@ class CScheduler
     typedef std::function<void()> Function;
 
     /** Call func at/after time t */
-    void schedule(Function f, std::chrono::system_clock::time_point t);
+    void schedule(Function f, std::chrono::steady_clock::time_point t);
 
     /** Call f once after the delta has passed */
     void scheduleFromNow(Function f, std::chrono::milliseconds delta)
     {
-        schedule(std::move(f), std::chrono::system_clock::now() + delta);
+        schedule(std::move(f), std::chrono::steady_clock::now() + delta);
     }
 
     /**
@@ -93,16 +93,16 @@ class CScheduler
      * Returns number of tasks waiting to be serviced,
      * and first and last task times
      */
-    size_t getQueueInfo(std::chrono::system_clock::time_point& first,
-                        std::chrono::system_clock::time_point& last) const;
+    size_t getQueueInfo(std::chrono::steady_clock::time_point& first,
+                        std::chrono::steady_clock::time_point& last) const;
 
     /** Returns true if there are threads actively running in serviceQueue() */
     bool AreThreadsServicingQueue() const;
 
 private:
     mutable Mutex newTaskMutex;
     std::condition_variable newTaskScheduled;
-    std::multimap<std::chrono::system_clock::time_point, Function> taskQueue GUARDED_BY(newTaskMutex);
+    std::multimap<std::chrono::steady_clock::time_point, Function> taskQueue GUARDED_BY(newTaskMutex);
     int nThreadsServicingQueue GUARDED_BY(newTaskMutex){0};
     bool stopRequested GUARDED_BY(newTaskMutex){false};
     bool stopWhenEmpty GUARDED_BY(newTaskMutex){false};

src/test/scheduler_tests.cpp

@@ -15,13 +15,13 @@
 
 BOOST_AUTO_TEST_SUITE(scheduler_tests)
 
-static void microTask(CScheduler& s, std::mutex& mutex, int& counter, int delta, std::chrono::system_clock::time_point rescheduleTime)
+static void microTask(CScheduler& s, std::mutex& mutex, int& counter, int delta, std::chrono::steady_clock::time_point rescheduleTime)
 {
     {
         std::lock_guard<std::mutex> lock(mutex);
         counter += delta;
     }
-    std::chrono::system_clock::time_point noTime = std::chrono::system_clock::time_point::min();
+    auto noTime = std::chrono::steady_clock::time_point::min();
     if (rescheduleTime != noTime) {
         CScheduler::Function f = std::bind(&microTask, std::ref(s), std::ref(mutex), std::ref(counter), -delta + 1, noTime);
         s.schedule(f, rescheduleTime);
@@ -49,15 +49,15 @@ BOOST_AUTO_TEST_CASE(manythreads)
     auto randomMsec = [](FastRandomContext& rc) -> int { return -11 + (int)rc.randrange(1012); }; // [-11, 1000]
     auto randomDelta = [](FastRandomContext& rc) -> int { return -1000 + (int)rc.randrange(2001); }; // [-1000, 1000]
 
-    std::chrono::system_clock::time_point start = std::chrono::system_clock::now();
-    std::chrono::system_clock::time_point now = start;
-    std::chrono::system_clock::time_point first, last;
+    auto start = std::chrono::steady_clock::now();
+    auto now = start;
+    std::chrono::steady_clock::time_point first, last;
     size_t nTasks = microTasks.getQueueInfo(first, last);
     BOOST_CHECK(nTasks == 0);
 
     for (int i = 0; i < 100; ++i) {
-        std::chrono::system_clock::time_point t = now + std::chrono::microseconds(randomMsec(rng));
-        std::chrono::system_clock::time_point tReschedule = now + std::chrono::microseconds(500 + randomMsec(rng));
+        auto t = now + std::chrono::microseconds(randomMsec(rng));
+        auto tReschedule = now + std::chrono::microseconds(500 + randomMsec(rng));
         int whichCounter = zeroToNine(rng);
         CScheduler::Function f = std::bind(&microTask, std::ref(microTasks),
                                              std::ref(counterMutex[whichCounter]), std::ref(counter[whichCounter]),
@@ -75,14 +75,14 @@ BOOST_AUTO_TEST_CASE(manythreads)
         microThreads.emplace_back(std::bind(&CScheduler::serviceQueue, &microTasks));
 
     UninterruptibleSleep(std::chrono::microseconds{600});
-    now = std::chrono::system_clock::now();
+    now = std::chrono::steady_clock::now();
 
     // More threads and more tasks:
     for (int i = 0; i < 5; i++)
         microThreads.emplace_back(std::bind(&CScheduler::serviceQueue, &microTasks));
     for (int i = 0; i < 100; i++) {
-        std::chrono::system_clock::time_point t = now + std::chrono::microseconds(randomMsec(rng));
-        std::chrono::system_clock::time_point tReschedule = now + std::chrono::microseconds(500 + randomMsec(rng));
+        auto t = now + std::chrono::microseconds(randomMsec(rng));
+        auto tReschedule = now + std::chrono::microseconds(500 + randomMsec(rng));
         int whichCounter = zeroToNine(rng);
         CScheduler::Function f = std::bind(&microTask, std::ref(microTasks),
                                              std::ref(counterMutex[whichCounter]), std::ref(counter[whichCounter]),
@@ -111,8 +111,8 @@ BOOST_AUTO_TEST_CASE(wait_until_past)
     Mutex mtx;
     WAIT_LOCK(mtx, lock);
 
-    const auto no_wait= [&](const std::chrono::seconds& d) {
-        return condvar.wait_until(lock, std::chrono::system_clock::now() - d);
+    const auto no_wait = [&](const std::chrono::seconds& d) {
+        return condvar.wait_until(lock, std::chrono::steady_clock::now() - d);
     };
 
     BOOST_CHECK(std::cv_status::timeout == no_wait(std::chrono::seconds{1}));
@@ -183,7 +183,7 @@ BOOST_AUTO_TEST_CASE(mockforward)
     scheduler.scheduleFromNow(dummy, std::chrono::minutes{8});
 
     // check taskQueue
-    std::chrono::system_clock::time_point first, last;
+    std::chrono::steady_clock::time_point first, last;
     size_t num_tasks = scheduler.getQueueInfo(first, last);
     BOOST_CHECK_EQUAL(num_tasks, 3ul);
 
@@ -204,7 +204,7 @@ BOOST_AUTO_TEST_CASE(mockforward)
     BOOST_CHECK_EQUAL(counter, 2);
 
     // check that the time of the remaining job has been updated
-    std::chrono::system_clock::time_point now = std::chrono::system_clock::now();
+    auto now = std::chrono::steady_clock::now();
     int delta = std::chrono::duration_cast<std::chrono::seconds>(first - now).count();
     // should be between 2 & 3 minutes from now
     BOOST_CHECK(delta > 2*60 && delta < 3*60);