psched
psched is a lightweight library that provides a priority-based task scheduler for modern C++.
- The
pschedscheduler manages an array of concurrent queues, each queue assigned a priority-level - A task, when scheduled, is enqueued onto one of queues based on the task's priority
- A pool of threads executes ready tasks, starting with the highest priority
- The priority of starving tasks is modulated based on the age of the task
Getting Started
Consider the task set below. There are three periodic tasks: a, b and c.
| Task | Period (ms) | Burst Time (ms) | Priority |
|---|---|---|---|
| a | 250 | 130 | 0 (Lowest) |
| b | 500 | 390 | 1 |
| c | 1000 | 560 | 2 (Highest) |
Here, burst time refers to the amount of time required by the task for executing on CPU.
Create a PriorityScheduler
First, let's create a scheduler:
#include <iostream>
#include <psched/priority_scheduler.h>
using namespace psched;
int main() {
PriorityScheduler<threads<3>,
queues<3, maintain_size<100, discard::oldest_task>>,
aging_policy<
task_starvation_after<std::chrono::milliseconds, 250>,
increment_priority_by<1>
>>
scheduler;Create a Task
Create the first task, Task a like below. The task "performs work" for 130ms. The post-completion callback, called when the task has completed, can be used to study the temporal behavior of the task, e.g., waiting time, burst time, and turnaround time.
Task a(
// Task action
[] { std::this_thread::sleep_for(std::chrono::milliseconds(130)); },
// Task post-completion callback
[](const TaskStats &stats) {
std::cout << "[Task a] ";
std::cout << "Waiting time = " << stats.waiting_time() << "ms; ";
std::cout << "Burst time = " << stats.burst_time() << "ms; ";
std::cout << "Turnaround time = " << stats.turnaround_time() << "ms\n";
}
);Schedule the task
Now, we can write a simple periodic timer that schedules this task at priority<0>:
auto timer_a = std::thread([&scheduler, &a]() {
while (true) {
// Schedule the task
scheduler.schedule<priority<0>>(a);
// Sleep for 250ms and repeat
std::this_thread::sleep_for(std::chrono::milliseconds(250));
}
});Schedule more tasks
We can repeat the above code for tasks b and c:
Task b(
// Task action
[] { std::this_thread::sleep_for(std::chrono::milliseconds(390)); },
// Task post-completion callback
[](const TaskStats &stats) {
std::cout << "[Task b] ";
std::cout << "Waiting time = " << stats.waiting_time() << "ms; ";
std::cout << "Burst time = " << stats.burst_time() << "ms; ";
std::cout << "Turnaround time = " << stats.turnaround_time() << "ms\n";
});
auto timer_b = std::thread([&scheduler, &b]() {
while (true) {
scheduler.schedule<priority<1>>(b);
std::this_thread::sleep_for(std::chrono::milliseconds(500));
}
});
Task c(
// Task action
[] { std::this_thread::sleep_for(std::chrono::milliseconds(560)); },
// Task post-completion callback
[](const TaskStats &stats) {
std::cout << "[Task c] ";
std::cout << "Waiting time = " << stats.waiting_time() << "ms; ";
std::cout << "Burst time = " << stats.burst_time() << "ms; ";
std::cout << "Turnaround time = " << stats.turnaround_time() << "ms\n";
});
auto timer_c = std::thread([&scheduler, &c]() {
while (true) {
scheduler.schedule<priority<2>>(c);
std::this_thread::sleep_for(std::chrono::milliseconds(1000));
}
});
timer_a.join();
timer_b.join();
timer_c.join();
}Running this sample may yield the following output:
./multiple_periodic_tasks
[Task a] Waiting time = 0ms; Burst time = 133ms; Turnaround time = 133ms
[Task c] Waiting time = 0ms; Burst time = 563ms; Turnaround time = 563ms
[Task b] Waiting time = 0ms; Burst time = 395ms; Turnaround time = 395ms
[Task a] Waiting time = 60ms; Burst time = 134ms; Turnaround time = 194ms
[Task a] Waiting time = 0ms; Burst time = 131ms; Turnaround time = 131ms
[Task b] Waiting time = 0ms; Burst time = 390ms; Turnaround time = 390ms
[Task a] Waiting time = 3ms; Burst time = 135ms; Turnaround time = 139ms
[Task a] Waiting time = 0ms; Burst time = 132ms; Turnaround time = 132ms
[Task b] Waiting time = 8ms; Burst time = 393ms; Turnaround time = 402ms
[Task c] Waiting time = 0ms; Burst time = 561ms; Turnaround time = 561ms
[Task a] Waiting time = 6ms; Burst time = 133ms; Turnaround time = 139ms
[Task b] Waiting time = [Task a] Waiting time = 0ms; Burst time = 393ms; Turnaround time = 393ms
0ms; Burst time = 133ms; Turnaround time = 133ms
[Task a] Waiting time = 11ms; Burst time = 134ms; Turnaround time = 145ms
[Task a] Waiting time = 0ms; Burst time = 134ms; Turnaround time = 134ms
[Task b] Waiting time = 11ms; Burst time = 394ms; Turnaround time = 405ms
[Task c] Waiting time = 0ms; Burst time = 560ms; Turnaround time = 560ms
[Task a] Waiting time = 7ms; Burst time = 132ms; Turnaround time = 139ms
[Task b] Waiting time = 0ms; Burst time = 390ms; Turnaround time = 390ms
[Task a] Waiting time = 0ms; Burst time = 130ms; Turnaround time = 130ms
[Task a] Waiting time = 17ms; Burst time = 130ms; Turnaround time = 148ms
[Task a] Waiting time = 0ms; Burst time = 131ms; Turnaround time = 131ms
[Task b] Waiting time = 10ms; Burst time = 390ms; Turnaround time = 401ms
[Task c] Waiting time = 0ms; Burst time = 560ms; Turnaround time = 560msBuilding Samples
git clone https://github.com/p-ranav/psched
cd psched
mkdir build && cd build
cmake -DPSCHED_SAMPLES=ON ..
makeGenerating Single Header
python3 utils/amalgamate/amalgamate.py -c single_include.json -s .Contributing
Contributions are welcome, have a look at the CONTRIBUTING.md document for more information.
License
The project is available under the MIT license.