What is the ```uint32_t _count;``` variable used for in Mutex Class?

[daniel-cesarini-tridonic-com]

Description

What is the uint32_t _count; variable used for?

mbed-os/rtos/Mutex.h

Line 156 in 30e39ee

uint32_t _count;

It is being increased:

mbed-os/rtos/Mutex.cpp

Line 56 in 30e39ee

_count++;

and decreased:

mbed-os/rtos/Mutex.cpp

Line 90 in 30e39ee

_count--;

but I do not see any other usage.

Issue request type

[X] Question
[ ] Enhancement
[ ] Bug

FYI: @c1728p9 @MarceloSalazar @geky, @kjbracey-arm, @sg-

[daniel-cesarini-tridonic-com]

FYI: @andreas-myka-tridonic-com, @markus-becker-tridonic-com

[kjbracey]

It's for debugging purposes only. Was introduced in #3648.

Only "use" is this in CondtionVariable.cpp:

MBED_ASSERT(_mutex._count == 1);

[daniel-cesarini-tridonic-com]

Should it then be "stripped" out in RELEASE build?

[kjbracey]

This was discussed in the review (with me on the "let's not have it there" side):

#3648 (comment)

I did compensate for it going in by taking out another 16 bytes.

#5428

There is a problem with adding/removing it for debug/release, and that's binary compatibility. The Mutex changes did cause issues with some binary drivers: #5547

Don't think we can afford different structure layout for those core classes based on build type :(

[ciarmcom]

ARM Internal Ref: MBOTRIAGE-40

[kjbracey]

I believe the question is answered.