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// Copyright (c) 2015-2022 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 <sync.h>
#include <util/syscall_sandbox.h>
#include <util/time.h>
#include <cassert>
#include <functional>
#include <utility>
CScheduler::CScheduler() = default;
CScheduler::~CScheduler()
{
assert(nThreadsServicingQueue == 0);
if (stopWhenEmpty) assert(taskQueue.empty());
}
void CScheduler::serviceQueue()
{
SetSyscallSandboxPolicy(SyscallSandboxPolicy::SCHEDULER);
WAIT_LOCK(newTaskMutex, lock);
++nThreadsServicingQueue;
// newTaskMutex is locked throughout this loop EXCEPT
// when the thread is waiting or when the user's function
// is called.
while (!shouldStop()) {
try {
while (!shouldStop() && 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:
while (!shouldStop() && !taskQueue.empty()) {
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
}
}
// If there are multiple threads, the queue can empty while we're waiting (another
// thread may service the task we were waiting on).
if (shouldStop() || 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:
REVERSE_LOCK(lock);
f();
}
} catch (...) {
--nThreadsServicingQueue;
throw;
}
}
--nThreadsServicingQueue;
newTaskScheduled.notify_one();
}
void CScheduler::schedule(CScheduler::Function f, std::chrono::steady_clock::time_point t)
{
{
LOCK(newTaskMutex);
taskQueue.insert(std::make_pair(t, f));
}
newTaskScheduled.notify_one();
}
void CScheduler::MockForward(std::chrono::seconds delta_seconds)
{
assert(delta_seconds > 0s && delta_seconds <= 1h);
{
LOCK(newTaskMutex);
// use temp_queue to maintain updated schedule
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);
}
// point taskQueue to temp_queue
taskQueue = std::move(temp_queue);
}
// notify that the taskQueue needs to be processed
newTaskScheduled.notify_one();
}
static void Repeat(CScheduler& s, CScheduler::Function f, std::chrono::milliseconds delta)
{
f();
s.scheduleFromNow([=, &s] { Repeat(s, f, delta); }, delta);
}
void CScheduler::scheduleEvery(CScheduler::Function f, std::chrono::milliseconds delta)
{
scheduleFromNow([this, f, delta] { Repeat(*this, f, delta); }, delta);
}
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();
if (!taskQueue.empty()) {
first = taskQueue.begin()->first;
last = taskQueue.rbegin()->first;
}
return result;
}
bool CScheduler::AreThreadsServicingQueue() const
{
LOCK(newTaskMutex);
return nThreadsServicingQueue;
}
void SingleThreadedSchedulerClient::MaybeScheduleProcessQueue()
{
{
LOCK(m_callbacks_mutex);
// Try to avoid scheduling too many copies here, but if we
// accidentally have two ProcessQueue's scheduled at once its
// not a big deal.
if (m_are_callbacks_running) return;
if (m_callbacks_pending.empty()) return;
}
m_scheduler.schedule([this] { this->ProcessQueue(); }, std::chrono::steady_clock::now());
}
void SingleThreadedSchedulerClient::ProcessQueue()
{
std::function<void()> callback;
{
LOCK(m_callbacks_mutex);
if (m_are_callbacks_running) return;
if (m_callbacks_pending.empty()) return;
m_are_callbacks_running = true;
callback = std::move(m_callbacks_pending.front());
m_callbacks_pending.pop_front();
}
// RAII the setting of fCallbacksRunning and calling MaybeScheduleProcessQueue
// to ensure both happen safely even if callback() throws.
struct RAIICallbacksRunning {
SingleThreadedSchedulerClient* instance;
explicit RAIICallbacksRunning(SingleThreadedSchedulerClient* _instance) : instance(_instance) {}
~RAIICallbacksRunning()
{
{
LOCK(instance->m_callbacks_mutex);
instance->m_are_callbacks_running = false;
}
instance->MaybeScheduleProcessQueue();
}
} raiicallbacksrunning(this);
callback();
}
void SingleThreadedSchedulerClient::AddToProcessQueue(std::function<void()> func)
{
{
LOCK(m_callbacks_mutex);
m_callbacks_pending.emplace_back(std::move(func));
}
MaybeScheduleProcessQueue();
}
void SingleThreadedSchedulerClient::EmptyQueue()
{
assert(!m_scheduler.AreThreadsServicingQueue());
bool should_continue = true;
while (should_continue) {
ProcessQueue();
LOCK(m_callbacks_mutex);
should_continue = !m_callbacks_pending.empty();
}
}
size_t SingleThreadedSchedulerClient::CallbacksPending()
{
LOCK(m_callbacks_mutex);
return m_callbacks_pending.size();
}
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