Distributed Mutex Lock

A mutual exclusion C API for shared NFS mounted systems

NOTE: dsm_lock_api assumes that the API is being called by processes running on different Linux machines. It relies on the $HOME/process.hosts file to obtain machine IPs that are participating in the Lock/Unlock operations. The presence of a shared file system across these machines is recommended to ensure consistent access to the $HOME/process.hosts file.

Features

• Plug and play API 🕹️✨

• Logs all background activity 🗒️

• Uses Lamport Scalar Clock ⏱️ for synchronization

• Spawns a network thread 🧵 to receive incoming messages 👂🏼

• Performs background operations in a non-blocking manner 🟢

• Uses semaphores for blocking ⛔ when requesting for lock

• dsm_init() initializes 📦 the ds_lock structure

• dsm_lock() sends a REQUEST to all other hosts to acquire lock 🔒

• dsm_lock() blocks 🛑 the callee thread until every host sends a REPLY

• dsm_unlock() well 🤷🏻‍♂️ unlocks the acquired lock 🔓

• dsm_destroy() disposes the ds_lock structure 🗑️

Usage

#include "dsm_lock_api.h" // Include the API header file


int main(int argc, char *argv[]){
    ds_lock *ds_lck = malloc(sizeof(ds_lock)); //Initialize the ds_lock struct pointer

    dsm_lock(ds_lck); // Request for lock

    do_something(); // Perform operation on a shared resource

    dsm_unlock(ds_lck); // Remove the lock

    dsm_destroy(ds_lck); // Dispose the ds_lock struct pointer

    return 0;
}

Compilation

Use the following command to compile my_prog.c which uses the dsm_lock_api.c.

$ gcc -o my_prog my_prog.c dsm_lock_api.c -lpthread

Note: make sure to use -lpthread flag to link the pthread library

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More information

The system given below share the $HOME directory. The grey color indicate that the machines currently do not use the dsm_lock_api.

dsm_init()

When a program calls the dsm_init() function the IP address of the current machine is added to the $HOME/process.hosts file. The blue machines means that other machines now know each other blue machine.

dsm_lock()

Scenario 1:

Machine C calls the dsm_lock() function. A packet with type REQUEST is sent from machine C to A, D, E and machine C waits till a REPLY packet is received from every machine.

Scenario 2:

Now, if machine C currently holds the lock and machine D wants the lock, machine D simply sends a REQUEST packet to all other machines and waits till the REPLY packet is received.

The following GIF shows that machine C does not send a REPLY packet until it releases the lock (using the dsm_unlock()).

dsm_destroy() (Unimplemented: See issue #3)

Remove the current machine's IP address and reorder the index also notify other hosts that a machine went offline.