Make the code usable when the RTOS is not compiled

[bogdanm]

This code implements a fake Mutex object (that doesn't do anything)
which is only used when the RTOS is not compiled.

[bogdanm]

@deepikabhavnani @geky
Background: we're trying to reduce the code size in our bootloader, and one of the things that we're getting rid of is the RTOS. This library needs a fix so that it can be used in non-RTOS environments. This is probably not the best place for a fake Mutex object, but I created this PR so that we can discuss possible solution.
@LiyouZhou @marcuschangarm

[marcuschangarm]

I think you should put it into mbed OS proper. There is already precedence for no-rtos implementation of core code: https://github.com/ARMmbed/mbed-os/blob/master/platform/mbed_wait_api_no_rtos.c

We have a whole set of block devices and other libraries that already have Mutex included. Putting it in mbed OS would solve the problem once and for all.

[deepikabhavnani]

Non-rtos implementation in mbed-os is taken care of. See https://github.com/ARMmbed/mbed-os/blob/7b428916f5b35da28a1b18e2c149c1115bb89d92/platform/PlatformMutex.h for more information. All drivers use PlatformMutex instead of rtos::mutex.

@geky - Any idea/background why PlatformMutex was not used in SD driver?

[geky]

@geky - Any idea/background why PlatformMutex was not used in SD driver?

There's not a reason, they should all be using PlatformMutex. 👍

Though IMO the Mutex class should behave this way by default.

[deepikabhavnani]

@bogdanm - Please try PlatformMutex and let us know the results.

[bogdanm]

@deepikabhavnani It works with PlatformMutex. As a side effect, I can just add Mutex=PlatformMutex in the macros section of my mbed_app.json, and the code just compiles :) Of course that's not the proper fix, but it does mean that I don't need this PR anymore. So I'll close it and I'll add an issue.

[marcuschangarm]

I can just add Mutex=PlatformMutex in the macros section of my mbed_app.json, and the code just compiles :)

I'm feeling dirty just by reading that comment! 😄