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I am developing an application with a realtime context.

One of the threads that executes in realtime context dequeues Task message objects from a mailbox (with real-time capabilities). Those Task messages contain a std::promise and a command.

After the thread gets the Task it executes the command and after that, std::promise::set_value() will be called.

Because of that, I am concerned that calling std::promise::set_value() might not have real-time capability.

Does anybody knows if set::value() internally allocates heap storage or does something else that would break the real-time capability?

Here is some snipplet to hopefully make my question clearer:

void RealTimeThread::exec() { while( active_ ) { Task receivedTask; if( mailbox_.getMailTimed( receivedTask, std::chrono::milliseconds( 100 ) ) ) { try { if( receivedTask.cmd ) { receivedTask.cmd->execute(); } else { // TODO: some internal actions on timeout throw std::runtime_error{"Command invalid"}; } // does the following call has real-time capabilities? receivedTask.cmdPromise.set_value(); } catch( ... ) { receivedTask.cmdPromise.set_exception( std::current_exception() ); } } } }
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    Aside: you seem to be replicating packaged_task Commented Jan 18, 2018 at 10:19
  • Thank you, that was new to me. Commented Jan 18, 2018 at 10:25
  • It's too bad that nobody can help me :-/ Commented Feb 1, 2018 at 7:49

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If anybody is interested:

A std::promise can be constructed given a allocator. This is used to allocated the "shared state" which is used on the std::future objects.

If you can provide an allocator that allocated on realtime (deterministic) it is fine to use std::promise in such context. Such an allocator is motley allocating from a memory block that was allocated before application entered realtime context.

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