mutex — mutex module¶
mutex module is used for creating mutexes.
class Mutex – mutex object¶
A mutex is an object enabling threads of execution to protect critical sections of code from reentrancy or to temporarily protect critical data sets from being updated by other threads. The term “mutex” derives from the notion of mutual exclusion. A mutex usually provides three methods:
In this implementation lock and unlock is controlled by a context manager.
In the context of MicroPython a mutex provides a mechanism where an interrupt service routine (ISR) can test whether the main loop was using critical variables at the time the interrupt occurred, and if so avoid modifying those variables. Typical usage:
import pyb, mutex mutex = mutex.Mutex() data_ready = False def callback(): # Timer or interrupt callback global data_ready if mutex.test(): data_ready = True # Update critical variables mutex.release() else: # defer any update # Associate callback with device (pin or timer) while True: # code if data_ready: with mutex: data_ready = False # Access critical variables # more code
Note that the with statement will execute immediately because no other process runs a with block on the same mutex instance.
References describing mutex and semaphore objects