Dining Philosophers

Overview

An implementation of a solution to the Dining Philosophers problem (a classic multi-thread synchronization problem). This particular implementation demonstrates the usage of multiple preemptible and cooperative threads of differing priorities, as well as dynamic mutexes and thread sleeping.

The philosopher always tries to get the lowest fork first (f1 then f2). When done, he will give back the forks in the reverse order (f2 then f1). If he gets two forks, he is EATING. Otherwise, he is THINKING. Transitional states are shown as well, such as STARVING when the philosopher is hungry but the forks are not available, and HOLDING ONE FORK when a philosopher is waiting for the second fork to be available.

Each Philosopher will randomly alternate between the EATING and THINKING state.

It is possible to run the demo in coop-only or preempt-only mode. To achieve this, set these values for CONFIG_NUM_COOP_PRIORITIES and CONFIG_NUM_PREEMPT_PRIORITIES in prj.conf:

preempt-only:

CONFIG_NUM_PREEMPT_PRIORITIES 6 CONFIG_NUM_COOP_PRIORITIES 0

coop-only:

CONFIG_NUM_PREEMPT_PRIORITIES 0 CONFIG_NUM_COOP_PRIORITIES 6

In these cases, the philosopher threads will run with priorities 0 to 5 (preempt-only) and -7 to -2 (coop-only).

Building and Running

This project outputs to the console. It can be built and executed on QEMU as follows:

Using west:

west build -t run

Using CMake and ninja:

cmake -B build -GNinja -DBOARD=qemu_x86 samples/philosophers
ninja -C build run

Sample Output

Philosopher 0 [P: 3]  HOLDING ONE FORK
Philosopher 1 [P: 2]  HOLDING ONE FORK
Philosopher 2 [P: 1]  EATING  [ 1900 ms ]
Philosopher 3 [P: 0]  THINKING [ 2500 ms ]
Philosopher 4 [C:-1]  THINKING [ 2200 ms ]
Philosopher 5 [C:-2]  THINKING [ 1700 ms ]