Resumable tasks#

[scheduler.resumable_tasks]

Functions to suspend task execution at a specific point and signal to resume it later.

// Defined in header <oneapi/tbb/task.h>

using oneapi::tbb::task::suspend_point = /* implementation-defined */;
template < typename Func > void oneapi::tbb::task::suspend( Func );
void oneapi::tbb::task::resume( oneapi::tbb::task::suspend_point );

Requirements:

The oneapi::tbb::task::suspend function called within a running task suspends execution of the task and switches the thread to participate in other oneTBB parallel work. This function accepts a user callable object with the current execution context oneapi::tbb::task::suspend_point as an argument. The user-specified callable object is executed by the calling thread.

The oneapi::tbb::task::suspend_point context tag must be passed to the oneapi::tbb::task::resume function to trigger a program execution at the suspended point. The oneapi::tbb::task::resume function can be called at any point of an application, even on a separate thread. In this regard, this function acts as a signal for the task scheduler.

Note

There are no guarantees that the same thread that called oneapi::tbb::task::suspend continues execution after the suspended point. However, these guarantees are provided for the outermost blocking oneTBB calls (such as oneapi::tbb::parallel_for and oneapi::tbb::flow::graph::wait_for_all) and oneapi::tbb::task_arena::execute calls.

Example#

// Parallel computation region
oneapi::tbb::parallel_for(0, N, [&](int) {
    // Suspend the current task execution and capture the context
    oneapi::tbb::task::suspend([&] (oneapi::tbb::task::suspend_point tag) {
        // Dedicated user-managed activity that processes async requests.
        async_activity.submit(tag); // could be OpenCL/IO/Database/Network etc.
    }); // execution will be resumed after this function
});

// Dedicated user-managed activity:

// Signal to resume execution of the task referenced by the oneapi::tbb::task::suspend_point
// from a dedicated user-managed activity
oneapi::tbb::task::resume(tag);