Tag: c++

A simplification to the job scheduler from the previous post is to pass the job function to the thread managing the job call, instead of making a shared pointer and capture it in the lambda.

The schedule method changes to:

void Scheduler::schedule(const Job f, long n) {
    std::unique_lock<std::mutex> lock(this->mutex);
    condition.wait(lock, [this] { return this->count < this->size; });
    count++;

    std::thread thread{
            [this](const Job f, long n) {
                std::this_thread::sleep_for(std::chrono::milliseconds(n));

                try {
                    (*f)();
                } catch (const std::exception &e) {
                    this->error(e);
                } catch (...) {
                    this->error(std::runtime_error("Unknown error"));
                }

                condition.notify_one();
                count--;
            }, f, n
    };
    thread.detach();
}

Not long ago I started writing some C++ code, and a task that I enjoyed implementing was a very basic job scheduler (idea from dailycodingproblem.com). I’m sure there are “holes” to be filled in my implementation regarding performance, concurrency, and general correctness. This is an early dive into the language and this post is mostly for me, to explain some things to myself.

The scheduler takes a job (function) and a time (in milliseconds) and runs the job after the given time.

The first thing was to define a function pointer as the job type.

using Job = void (*)();

 

Another callback that I’ll be using is one to report job errors, which takes an exception as an argument.

using Error = void (*)(const std::exception &);

 

The scheduler class constructor takes a size and an error callback (to report errors). The size is the maximum number of jobs accepted until scheduling blocks and waits for a job to be finished.
An error callback is required. The first measure to ensure this is to delete the constructor that takes null for the error callback, which performs a compile-time check. Explicitly passing null will not be allowed, but a pointer that is null will be checked at runtime.

Scheduler(size_t size, Error error);
Scheduler(size_t size, nullptr_t) = delete;

Continue reading A job scheduler in C++