[riot-notifications] [RIOT-OS/RIOT] core: Added thread_signal & thread_await_signal (#11006)

Marian Buschsieweke notifications at github.com
Tue Feb 12 16:54:29 CET 2019

### Contribution description

`thread_sleep()` and `thread_wakeup()` provide simple means to signal an event to a thread. However, the calls need to be synchronized: The waiting thread has to call `thread_sleep()` before `thread_wakeup()` is called.

This commit adds `thread_await_signal()` and `thread_signal()` which do not need to be synchronized: If `thread_signal()` is called between to calls to `thread_await_signal()`, the second call to `thread_await_signal()` will return immediately. If `thread_await_signal()` is called before the matching call to `thread_signal()`, they will behave like `thread_wakeup()` and `thread_sleep()`.

### Testing procedure

As `thread_sleep()` and `thread_wakeup()` are changed to internally use `thread_await_signal()` and `thread_signal()`, testing if they still work should be done. `thread_await_signal()` and `thread_signal()` could be tested with https://github.com/RIOT-OS/RIOT/pull/10340, which I will update to use this PR after my next appointment. I could also provide a minimum example application using both APIs, if needed be.

### Issues/PRs references

Used in PR https://github.com/RIOT-OS/RIOT/pull/10340 to make `netdev_driver_t::send()` blocking while still handling ISRs in a way that does not block the CPU for a couple of milliseconds. PR https://github.com/RIOT-OS/RIOT/pull/8304 be rewritten to use this more lightweight API instead of `thread_flags`. (To avoid confusion: This API is unable to replace `thread_flags` and does not want to do this. But in the use cases both could be used, this API is more lightweight.) Maybe also `at86rf2xx` implementation to make `netdev_driver_t::send()` blocking while waiting TX to complete could use this API and an interrupt instead of busy waiting for TX to complete.
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-- Commit Summary --

  * core: Added thread_signal & thread_await_signal

-- File Changes --

    M core/include/thread.h (80)
    M core/thread.c (31)

-- Patch Links --


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