| .. _dining-philosophers-sample: |
| |
| 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: |
| |
| .. code-block:: console |
| |
| $ cd samples/philosophers |
| $ make run |
| |
| Sample Output |
| ============= |
| |
| .. code-block:: console |
| |
| 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 ] |
| |
| |