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std::packaged_task::operator()

void operator()( ArgTypes... args );

(since C++11)

Calls the stored task with args as the arguments. The return value of the task or any exceptions thrown are stored in the shared state. The shared state is made ready and any threads waiting for this are unblocked.

Parameters

args

the parameters to pass on invocation of the stored task

Return value

(none).

Exceptions

std::future_error on the following error conditions:

The stored task has already been invoked. The error category is set to promise_already_satisfied.
*this has no shared state. The error category is set to no_state.

Notes

A successful call to `operator()` synchronizes with a call to any member function of a `std::future` or `std::shared_future` that share their shared state with `*this`.	(until C++14)
No additional synchronization guarantees other than what's already provided by shared state.	(since C++14)