| .. _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: |
| |
| .. zephyr-app-commands:: |
| :zephyr-app: samples/philosophers |
| :host-os: unix |
| :board: qemu_x86 |
| :goals: run |
| :compact: |
| |
| 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 ] |
| |
| Exit QEMU by pressing :kbd:`CTRL+A` :kbd:`x`. |
| |
| Debug Threads |
| ************* |
| |
| The philosophers sample by default enables :kconfig:option:`CONFIG_DEBUG_THREAD_INFO`. |
| This allows tools like OpenOCD and J-link to inspect thread data using |
| ``info threads``. |
| |
| .. zephyr-app-commands:: |
| :zephyr-app: samples/philosophers |
| :host-os: unix |
| :board: <board_name> |
| :goals: debug |
| :compact: |
| |
| |
| OpenOCD Sample Output |
| ===================== |
| |
| .. code-block:: console |
| |
| Thread 1 received signal SIGINT, Interrupt. |
| [Switching to Thread 537003160] |
| arch_cpu_idle () at zephyr/mainline/zephyr/arch/arm/core/cpu_idle.S:107 |
| 107 cpsie i |
| (gdb) i threads |
| Id Target Id Frame |
| * 1 Thread 537003160 (Name: idle 00, prio:40,useropts:1) arch_cpu_idle () at zephyr/mainline/zephyr/arch/arm/core/cpu_idle.S:107 |
| Info : Getting thread 537002984 reg list |
| 2 Thread 537002984 (Name: Philosopher 5, prio:-2,useropts:4) 0x08001404 in arch_irq_unlock (key=0) at zephyr/mainline/zephyr/include/arch/arm/asm_inline_gcc.h:95 |
| Info : Getting thread 537002808 reg list |
| 3 Thread 537002808 (Name: Philosopher 4, prio:-1,useropts:4) 0x08001404 in arch_irq_unlock (key=0) at zephyr/mainline/zephyr/include/arch/arm/asm_inline_gcc.h:95 |
| Info : Getting thread 537002632 reg list |
| 4 Thread 537002632 (Name: Philosopher 3, prio:0,useropts:4) 0x08001404 in arch_irq_unlock (key=0) at zephyr/mainline/zephyr/include/arch/arm/asm_inline_gcc.h:95 |
| Info : Getting thread 537002456 reg list |
| 5 Thread 537002456 (Name: Philosopher 2, prio:1,useropts:4) 0x08001404 in arch_irq_unlock (key=0) at zephyr/mainline/zephyr/include/arch/arm/asm_inline_gcc.h:95 |
| Info : Getting thread 537002280 reg list |
| 6 Thread 537002280 (Name: Philosopher 1, prio:2,useropts:4) 0x08001404 in arch_irq_unlock (key=0) at zephyr/mainline/zephyr/include/arch/arm/asm_inline_gcc.h:95 |
| Info : Getting thread 537002104 reg list |
| 7 Thread 537002104 (Name: Philosopher 0, prio:3,useropts:4) 0x08001404 in arch_irq_unlock (key=0) at zephyr/mainline/zephyr/include/arch/arm/asm_inline_gcc.h:95 |
| |
| .. code-block:: console |
| |
| Philosopher 0 [P: 3] STARVING |
| Philosopher 1 [P: 2] HOLDING ONE FORK |
| Philosopher 2 [P: 1] EATING [ 400 ms ] |
| Philosopher 3 [P: 0] THINKING [ 525 ms ] |
| Philosopher 4 [C:-1] HOLDING ONE FORK |
| Philosopher 5 [C:-2] EATING [ 625 ms ] |
| |
| |
| J-Link Sample Output |
| ==================== |
| |
| .. code-block:: console |
| |
| Thread 2 received signal SIGTRAP, Trace/breakpoint trap. |
| [Switching to Thread 537920592] |
| arch_cpu_idle () at zephyr/mainline/zephyr/arch/arm/core/cpu_idle.S:107 |
| 107 cpsie i |
| (gdb) i threads |
| Id Target Id Frame |
| * 2 Thread 537920592 (idle 00 UNKNOWN PRIO 40) arch_cpu_idle () at zephyr/mainline/zephyr/arch/arm/core/cpu_idle.S:107 |
| 3 Thread 537919536 (Philosopher 0 PENDING PRIO 3) arch_swap (key=0) at zephyr/mainline/zephyr/arch/arm/core/swap.c:53 |
| 4 Thread 537919712 (Philosopher 1 SUSPENDED PRIO 2) arch_swap (key=key@entry=0) at zephyr/mainline/zephyr/arch/arm/core/swap.c:53 |
| 5 Thread 537919888 (Philosopher 2 SUSPENDED PRIO 1) arch_swap (key=key@entry=0) at zephyr/mainline/zephyr/arch/arm/core/swap.c:53 |
| 6 Thread 537920064 (Philosopher 3 SUSPENDED PRIO 0) arch_swap (key=key@entry=0) at zephyr/mainline/zephyr/arch/arm/core/swap.c:53 |
| 7 Thread 537920240 (Philosopher 4 PENDING PRIO 255) arch_swap (key=0) at zephyr/mainline/zephyr/arch/arm/core/swap.c:53 |
| 8 Thread 537920416 (Philosopher 5 SUSPENDED PRIO 254) arch_swap (key=key@entry=0) at zephyr/mainline/zephyr/arch/arm/core/swap.c:53 |
| |
| .. code-block:: console |
| |
| Philosopher 0 [P: 3] STARVING |
| Philosopher 1 [P: 2] EATING [ 475 ms ] |
| Philosopher 2 [P: 1] THINKING [ 700 ms ] |
| Philosopher 3 [P: 0] THINKING [ 525 ms ] |
| Philosopher 4 [C:-1] HOLDING ONE FORK |
| Philosopher 5 [C:-2] EATING [ 625 ms ] |
