Mutex and condition variable minix server

Mutexes

Functions:

• cs_lock(int mutex_id) - tries to reserve the mutex with the given ID. If the mutex is not currently owned by another process, it is assigned to the caller, and the function returns 0 (success). Otherwise the caller is suspended until the mutex can be assigned to it, and only then the function returns 0 (success).
• cs_unlock(int mutex_id) - releases the mutex with the given ID. If the caller is the owner of the mutex, the function returns 0 (success) and the server assigns the mutex to the next process in the queue. Otherwise the function returns -1 and sets errno to EPERM.

Condition variables

Functions:

• cs_wait(int cond_var_id, int mutex_id) - suspends current process, awaiting event cond_var_id. The calling process should be the owner of the mutex mutex_id, otherwise the function returns -1 and sets errno to EINVAL. If the calling process is the owner of mutex_id mutex, the server releases the mutex and suspends the caller until another process calls cond_var_id event. In such case, the server enqueues process as awaiting for mutex_id mutex and the function returns 0 once the mutex has been obtained.
• cs_broadcast(int cond_var_id) - broadcasts cond_var_id event. All processes awaiting cond_var_id event are unsuspended and each of them resumes after regaining their mutex.

Signals

If the process was waiting for a mutex when it received a signal, it resumes waiting after handling it. If it was waiting for an event, it recovers the mutex and returns success (spurious wakeup).

Mutexes of terminated processes are immediately released.

Repository structure

The solution is designed to run in MINIX 3.2.1.

• src / reflects a fragment of the MINIX source directory structure. To test, copy the contents of the src directory from the repository to the /usr/src directory in MINIX. As a result, some of the original source files will be overwritten. Then install the includes, recompile and install the standard library and a new server. To enable changes to the basic system servers (PM), the system image must also be recompiled before testing. After rebooting the system, the new functionality should work after starting the server with the command service up /usr/sbin/cs.