[operating-system] Difference between binary semaphore and mutex

The answer may depend on the target OS. For example, at least one RTOS implementation I'm familiar with will allow multiple sequential "get" operations against a single OS mutex, so long as they're all from within the same thread context. The multiple gets must be replaced by an equal number of puts before another thread will be allowed to get the mutex. This differs from binary semaphores, for which only a single get is allowed at a time, regardless of thread contexts.

The idea behind this type of mutex is that you protect an object by only allowing a single context to modify the data at a time. Even if the thread gets the mutex and then calls a function that further modifies the object (and gets/puts the protector mutex around its own operations), the operations should still be safe because they're all happening under a single thread.

{
    mutexGet();  // Other threads can no longer get the mutex.

    // Make changes to the protected object.
    // ...

    objectModify();  // Also gets/puts the mutex.  Only allowed from this thread context.

    // Make more changes to the protected object.
    // ...

    mutexPut();  // Finally allows other threads to get the mutex.
}

Of course, when using this feature, you must be certain that all accesses within a single thread really are safe!

I'm not sure how common this approach is, or whether it applies outside of the systems with which I'm familiar. For an example of this kind of mutex, see the ThreadX RTOS.

Examples related to operating-system

Context.startForegroundService() did not then call Service.startForeground() Fork() function in C python: get directory two levels up Find Process Name by its Process ID Best way to find os name and version in Unix/Linux platform How to run a program without an operating system? How to make parent wait for all child processes to finish? Get operating system info Running windows shell commands with python What are the differences between virtual memory and physical memory?

Examples related to mutex

What is the Swift equivalent to Objective-C's "@synchronized"? Mutex lock threads When should one use a spinlock instead of mutex? Is there a Mutex in Java? Mutex example / tutorial? When should we use mutex and when should we use semaphore Proper use of mutexes in Python Lock, mutex, semaphore... what's the difference? Example for boost shared_mutex (multiple reads/one write)? What is mutex and semaphore in Java ? What is the main difference?

Examples related to semaphore

semaphore implementation "The semaphore timeout period has expired" error for USB connection Semaphore vs. Monitors - what's the difference? Is there a Mutex in Java? When should we use mutex and when should we use semaphore Lock, mutex, semaphore... what's the difference? Delete all SYSTEM V shared memory and semaphores on UNIX-like systems What is mutex and semaphore in Java ? What is the main difference? Difference between binary semaphore and mutex What is a semaphore?

Examples related to binary-semaphore

Difference between binary semaphore and mutex