Preemption

Preemption can also result in re-entrancy. How to deal with it? Assuming single-core systems there are two approaches:

1. Disable interrupts in acquire; re-enable them in release. This means that the logging macros block higher priority interrupts.

2. Have a separate logger per priority level. acquire and release are now lock-free and don't block interrupts. This requires multiplexing in the transport.