Synchronise tasks and protect shared resources.
A mutex gives exclusive access to a shared resource, a semaphore counts available resources or signals events. Misuse causes deadlock, priority inversion and race conditions. Use short critical sections; prefer message queues for data transfer.
Two tasks sharing a UART protect it with a mutex.
Shared resources must be protected from simultaneous access, or data becomes corrupted, so mutexes and semaphores are used in every multitasking system.
Synchronise tasks and protect shared resources.
Shared resources must be protected from simultaneous access, or data becomes corrupted, so mutexes and semaphores are used in every multitasking system.
A mutex guards a resource and is owned by one task. A semaphore is a counter for signalling or limiting access, and any task can post it.
When tasks wait for each other's resources forever, which can be avoided with consistent lock order and timeouts.
Typical applications include protecting a shared sensor buffer from two tasks, limiting access to a communication bus to one task at a time and signalling a task that new data has arrived using a semaphore.
Study "Task scheduling" first (topic 78 of 104 in Electronics & Embedded). It covers the groundwork this topic builds on.
Binary vs counting semaphores. Lock ordering. ISR-safe API variants.
Two tasks sharing a UART protect it with a mutex.
The next topic is "Priority inversion", which builds directly on this one.
It is classed as Advanced in Electronics & Embedded (topic 79 of 104). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Electronics & Embedded.
Want to practise? Open the interactive course for quick checks, quizzes, simulations and progress tracking.