Philosophers is a mandatory project from 42 School, based on the classic Dining Philosophers Problem.
The goal is to implement a correct and stable multi-threaded simulation using POSIX threads (pthread) and mutexes, while strictly avoiding data races, deadlocks, and undefined behavior.
- Threads: Each philosopher is represented by a thread.
- Mutexes: Each fork is protected by a mutex.
- Routine: Philosophers repeatedly: Eat Sleep Think.
- Death: A philosopher dies if they do not start eating within
time_to_die. - Completion: If
must_eatis provided, the simulation stops once all philosophers have eaten enough times.
To compile the project, run:
make
To rebuild from scratch:
make re
This will generate the executable: ./philo.
./philo number_of_philosophers time_to_die time_to_eat time_to_sleep [must_eat]
| Parameter | Description | Unit |
|---|---|---|
number_of_philosophers |
Number of philosophers (and forks) | count |
time_to_die |
Time limit before a philosopher dies without eating | ms |
time_to_eat |
Duration of the eating state | ms |
time_to_sleep |
Duration of the sleeping state | ms |
must_eat (optional) |
Minimum meals per philosopher to end simulation | count |
Each log line strictly follows the format:
<timestamp> <philosopher_id> <message>
Example:
200 3 is eating
400 3 is sleeping
- timestamp: milliseconds since the start of the simulation.
- philosopher_id: index starting from 1.
- Possible messages:
has taken a fork,is eating,is sleeping,is thinking,died.
- Philosopher Threads: One per philosopher.
- Monitoring Thread: A dedicated thread that:
- Detects philosopher death.
- Detects when all philosophers have eaten enough times.
- Fork Mutexes: One per fork.
- Philosopher Mutexes: One per philosopher to protect
last_meal_timeandmeals_eaten. - Global Mutexes:
- Print Mutex: Avoids scrambled output.
- State Mutex: Protects the global stop flag.
- Pick-up Order: Philosophers use different fork-picking orders based on their index (odd/even).
- Desynchronization: A dynamic thinking delay is introduced to desynchronize fork acquisition and reduce starvation risk.
- Millisecond precision using
gettimeofday. - Custom Sleep: An interruptible sleep function that periodically checks the global stop flag to ensure timely death detection (within 10ms as required).
- ✅ No data races (TSan verified)
- ✅ No memory leaks (Valgrind verified)
- ✅ Thread-safe logging
- ✅ Fully compliant with 42 evaluation requirements
Philosophers 是 42 学校的 Mandatory 项目之一，基于经典的并发问题 Dining Philosophers Problem。
本项目要求使用 POSIX 线程 (pthread) 与 互斥锁 (mutex)，在严格避免数据竞争、死锁和未定义行为的前提下，实现一个稳定的并发模拟程序。
- 线程模型：每个哲学家对应一个线程。
- 资源保护：每把叉子由一个互斥锁保护。
- 行为循环：哲学家循环执行：吃 睡 想。
- 死亡判定：若超过
time_to_die未开始进食，则哲学家死亡，模拟结束。 - 停止条件：若指定
must_eat，当所有哲学家吃够次数后，模拟自动结束。
编译项目：
make
重新编译：
make re
生成可执行文件：./philo。
./philo 哲学家数量 存活时间 吃饭时间 睡觉时间 [最少吃饭次数]
| 参数 | 含义 | 单位 |
|---|---|---|
哲学家数量 |
哲学家及叉子的总数 | 个 |
存活时间 |
多久未进食会死亡 | 毫秒 |
吃饭时间 |
吃饭动作持续的时间 | 毫秒 |
睡觉时间 |
睡觉动作持续的时间 | 毫秒 |
最少吃饭次数 (可选) |
每个哲学家必须达到的进食次数 | 次 |
程序输出严格遵循以下格式：
<时间戳> <哲学家编号> <状态信息>
示例：
200 3 is eating
400 3 is sleeping
- 时间戳：从程序启动开始计算的毫秒数。
- 哲学家编号：从 1 开始编号。
- 可能的状态：
has taken a fork,is eating,is sleeping,is thinking,died。
- 哲学家线程：每位哲学家一个独立线程。
- 监控线程：额外创建一个独立线程用于：
- 实时检测哲学家是否死亡。
- 检测是否所有哲学家已满足进食次数。
- 叉子锁：每把叉子对应一个
mutex。 - 哲学家锁：每个哲学家拥有独立的锁，用于保护
last_meal_time和已进食次数。 - 全局锁：
- 打印锁：防止多线程同时输出导致字符错乱。
- 状态锁：保护全局停止标志位（Stop Flag）。
- 拿叉顺序：根据哲学家编号的奇偶性，采用不同的拿叉顺序。
- 动态思考：在思考阶段引入微小的动态延迟，使线程错峰执行，降低资源竞争。
- 使用
gettimeofday获取毫秒级时间。 - 精准休眠：实现可中断的睡眠机制，在休眠过程中持续检测停止条件，确保死亡检测精度在 10ms 以内。
- ✅ 无数据竞争 (Data Race)
- ✅ 无内存泄漏 (Valgrind 认证)
- ✅ 日志输出线程安全
- ✅ 完整覆盖 Mandatory 要求，符合 42 评估标准