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使用Linux无名信号量实现了读写者线程的互斥和同步。
实验环境
环境#xff1a;Linux语言#xff1a;CCMake#xff1a;3.17.1GCC#xff1a;7.5.0IDE#xff1a;Clion 2020.3.1
实验目标
理解进程同步的两种制约关系#xff1a;互斥与…操作系统线程同步
使用Linux无名信号量实现了读写者线程的互斥和同步。
实验环境
环境Linux语言CCMake3.17.1GCC7.5.0IDEClion 2020.3.1
实验目标
理解进程同步的两种制约关系互斥与同步。掌握利用记录型信号量解决进程同步问题的方法。加深对进程同步控制的理解。
实验内容
以“生产者-消费者模型”为基础在Linux环境下创建一个控制进程在该进程中创建读者写者线程各一个模拟生产者和消费者它们使用N个不同的缓冲区N为一个确定的数值本实验中取N16。写者线程写入数据然后将数据放置在空缓冲区中供读者线程读取。读者线程从缓冲区中获得数据然后释放缓冲区。当写者线程写入数据时如果没有空缓冲区可用那么写者线程必须等待读者线程释放出一个空缓冲区。当读者线程读取数据时如果没有满的缓冲区那么读者线程将被阻塞直到缓冲区被写者线程写满。
可以作如下的实验尝试并观察和记录进程同步效果
没有信号量时实现生产者线程与消费者线程互斥制约用一个互斥信号量mutex用以阻止生产者线程和消费者线程同时操作缓冲区列表用一个信号量full当生产者线程生产出一个物品时可以用它向消费者线程发出信号用一个信号量empty消费者线程释放出一个空缓冲区时可以用它向生产者线程发出信号。同时使用2、3中的信号量实现生产者-消费者的互斥与同步制约
实验过程和结果
函数介绍
pthread.h
#include pthread.h/* Create a new thread, starting with execution of START-ROUTINEgetting passed ARG. Creation attributed come from ATTR. The newhandle is stored in *NEWTHREAD. */
extern int pthread_create (pthread_t *__restrict __newthread,const pthread_attr_t *__restrict __attr,void *(*__start_routine) (void *),void *__restrict __arg) __THROWNL __nonnull ((1, 3));/* Terminate calling thread.The registered cleanup handlers are called via exception handlingso we cannot mark this function with __THROW.*/
extern void pthread_exit (void *__retval) __attribute__ ((__noreturn__));/* Make calling thread wait for termination of the thread TH. Theexit status of the thread is stored in *THREAD_RETURN, if THREAD_RETURNis not NULL.This function is a cancellation point and therefore not marked with__THROW. */
extern int pthread_join (pthread_t __th, void **__thread_return);/* Obtain the identifier of the current thread. */
extern pthread_t pthread_self (void) __THROW __attribute__ ((__const__));/* Thread identifiers. The structure of the attribute type is notexposed on purpose. */
typedef unsigned long int pthread_t;semaphore.h
在 POSIX 标准中信号量分两种一种是无名信号量一种是有名信号量。无名信号量一般用于线程间同步或互斥而有名信号量一般用于进程间同步或互斥。它们的区别和管道及命名管道的区别类似无名信号量则直接保存在内存中而有名信号量要求创建一个文件。
无名信号量需要semaphore.h头文件有名信号量则需要sys/sem.h头文件。本文实现线程间同步和互斥故使用更为简便的无名信号量。
#include semaphore.htypedef union
{char __size[__SIZEOF_SEM_T];long int __align;
} sem_t;/* Initialize semaphore object SEM to VALUE. If PSHARED then share itwith other processes. */
extern int sem_init (sem_t *__sem, int __pshared, unsigned int __value)__THROW;/* Free resources associated with semaphore object SEM. */
extern int sem_destroy (sem_t *__sem) __THROW;This function is a cancellation point and therefore not marked with__THROW. */
extern int sem_wait (sem_t *__sem);/* Post SEM. */
extern int sem_post (sem_t *__sem) __THROWNL;CMake
# based on clion
cmake_minimum_required(VERSION 3.17)set(CMAKE_CXX_STANDARD 14)find_package(Threads REQUIRED)
add_executable(thread main.c ${SOURCE_FILES})
target_link_libraries(thread Threads::Threads)信号量用于互斥与同步 一、读、写者互斥
创建读者写者void *Read(void *arg)和void *Write(void *arg)由于只能有一个读者、一个写者可知读者之间是互斥的、写者之间也是互斥的故设置信号量sem_t read_sem和sem_t write_sem. 设置并初始化全局变量int buffer 0;模拟缓冲区的写入和读出。设置并初始化int read_write_flag[2] {1, 1};判断是否发生读写冲突。
//
// Created by Sylvan Ding on 2022/5/10.
//#include stdio.h
#include stdlib.h
#include unistd.h
#include pthread.h
#include semaphore.h#define N 16
#define MAX_PROCESS_NUM 100int buffer 0;
int read_write_flag[2] {1, 1};// sem
sem_t read_sem;
sem_t write_sem;void *Read(void *arg) {sem_wait(read_sem);read_write_flag[0] 0;int buf_temp;int duration rand() % 4;pthread_t tid pthread_self();printf(\033[32m[R] tid: %lu starts reading...\033[0m\n, tid);if (!read_write_flag[1])printf(\033[31m[R] tid: %lu conflicts with writing process!\033[0m\n, tid);// readbuf_temp buffer;sleep(duration);buffer 0;printf([R] tid: %lu has read all %d buffers!\n, tid, buf_temp);if (buf_temp N)printf(\033[33m[R] tid: %lu did not read entire 16 buffers!\033[0m\n, tid);read_write_flag[0] 1;sem_post(read_sem);return NULL;
}void *Write(void *arg) {sem_wait(write_sem);read_write_flag[1] 0;int res;int buf_temp;int size rand() % 16 1;int duration rand() % 5;pthread_t tid pthread_self();printf(\033[32m[W] tid: %lu starts writing...\033[0m\n, tid);// writebuf_temp buffer;res size buf_temp;sleep(duration);if (res N)buffer 16;elsebuffer res;printf([W] tid: %lu has written %d buffers, with %d buffers occupied!\n, tid, res N ? N - buf_temp : size,buffer);read_write_flag[1] 1;sem_post(write_sem);return NULL;
}int main(int argc, char *argv[]) {srand(888);int res 0;int randm 0;void *(*target)(void *) NULL;pthread_t myThreads[MAX_PROCESS_NUM];// init semif (sem_init(read_sem, 0, 1) 0) {printf(failed to init read_sem);exit(0);}if (sem_init(write_sem, 0, 1) 0) {printf(failed to init write_sem);exit(0);}for (int i 0; i MAX_PROCESS_NUM; i) {randm rand() % 4;if (i % 2)target Read;elsetarget Write;res pthread_create(myThreads[i], NULL, target, NULL);if (res 0) {printf(failed to create the thread!);exit(0);}sleep(randm);}void *thread_result NULL;for (int i 0; i MAX_PROCESS_NUM; i)res pthread_join(myThreads[i], thread_result);// destroy semsem_destroy(read_sem);sem_destroy(write_sem);return 0;
}二、读写者互斥
为实现读、写互斥设置mutex信号量编写void *Read1(void *arg)和void *Write1(void *arg).
sem_t mutex;void *Read1(void *arg) {sem_wait(mutex);Read(arg);sem_post(mutex);return NULL;
}void *Write1(void *arg) {sem_wait(mutex);Write(arg);sem_post(mutex);return NULL;
}void all_sem_init() {// init semint res 0;if (sem_init(read_sem, 0, 1) 0) {printf(failed to init read_sem);res -1;}if (sem_init(write_sem, 0, 1) 0) {printf(failed to init write_sem);res -1;}if (sem_init(mutex, 0, 1) 0) {printf(failed to init mutex);res -1;}if (res)exit(0);
}void all_sem_des() {// destroy semsem_destroy(read_sem);sem_destroy(write_sem);sem_destroy(mutex);
}int main(int argc, char *argv[]) {srand(888);int res 0;int randm 0;void *(*target)(void *) NULL;pthread_t myThreads[MAX_PROCESS_NUM];all_sem_init();for (int i 0; i MAX_PROCESS_NUM; i) {randm rand() % 4;if (i % 2)
// target Read;target Read1;else
// target Write;target Write1;res pthread_create(myThreads[i], NULL, target, NULL);if (res 0) {printf(failed to create the thread!);exit(0);}sleep(randm);}void *thread_result NULL;for (int i 0; i MAX_PROCESS_NUM; i)res pthread_join(myThreads[i], thread_result);all_sem_des();return 0;
}三、读写者同步
为了解决在缓冲区未满时读进程就读出缓冲区的问题设置full信号量。同时在缓冲区写满时阻塞写进程设置empty信号量。二者均初始化为0.
sem_t full;
sem_t empty;void all_sem_init() {// init semint res 0;// ...if (sem_init(full, 0, 0) 0) {printf(failed to init full);res -1;}if (sem_init(empty, 0, 0) 0) {printf(failed to init empty);res -1;}if (res)exit(0);
}void all_sem_des() {// destroy sem// ...sem_destroy(full);sem_destroy(empty);
}void *Read2(void *arg) {sem_wait(full);Read(arg);sem_post(empty);return NULL;
}void *Write2(void *arg) {Write(arg);if (buffer N) {sem_post(full);sem_wait(empty);}return NULL;
}int main(int argc, char *argv[]) {// ...for (int i 0; i MAX_PROCESS_NUM; i) {randm rand() % 4;if (i % 2) {
// target Read;
// target Read1;target Read2;} else {
// target Write;
// target Write1;target Write2;}// ...
}四、读写者同步且互斥
结合二、三的信号量实现读写同步且互斥。
void *Read3(void *arg) {sem_wait(full);sem_wait(mutex);Read(arg);sem_post(mutex);sem_post(empty);return NULL;
}void *Write3(void *arg) {sem_wait(mutex);Write(arg);sem_post(mutex);if (buffer N) {sem_post(full);sem_wait(empty);}return NULL;
}改进
因为只有一个读者、一个写者进程并非多读写者所以可以不用在main()中开多个线程可以只创建read()和write()两线程然后在线程内部使用while循环去访问buffer. 这个工作就留给读者自己去实现啦
附录完整实验代码
//
// Created by Sylvan Ding on 2022/5/10.
//#include stdio.h
#include stdlib.h
#include unistd.h
#include pthread.h
#include semaphore.h#define N 16
#define MAX_PROCESS_NUM 100int buffer 0;
int read_write_flag[2] {1, 1};// sem
sem_t read_sem;
sem_t write_sem;
sem_t mutex;
sem_t full;
sem_t empty;void *Read(void *arg) {sem_wait(read_sem);read_write_flag[0] 0;int buf_temp;int duration rand() % 4;pthread_t tid pthread_self();printf(\033[32m[R] tid: %lu starts reading...\033[0m\n, tid);if (!read_write_flag[1])printf(\033[31m[R] tid: %lu conflicts with writing process!\033[0m\n, tid);// readbuf_temp buffer;sleep(duration);buffer 0;printf([R] tid: %lu has read all %d buffers!\n, tid, buf_temp);if (buf_temp N)printf(\033[33m[R] tid: %lu did not read entire 16 buffers!\033[0m\n, tid);read_write_flag[0] 1;sem_post(read_sem);return NULL;
}void *Write(void *arg) {sem_wait(write_sem);read_write_flag[1] 0;int res;int buf_temp;int size rand() % 16 1;int duration rand() % 5;pthread_t tid pthread_self();printf(\033[32m[W] tid: %lu starts writing...\033[0m\n, tid);// writebuf_temp buffer;res size buf_temp;sleep(duration);if (res N)buffer 16;elsebuffer res;printf([W] tid: %lu has written %d buffers, with %d buffers occupied!\n, tid, res N ? N - buf_temp : size,buffer);read_write_flag[1] 1;sem_post(write_sem);return NULL;
}void *Read1(void *arg) {sem_wait(mutex);Read(arg);sem_post(mutex);return NULL;
}void *Write1(void *arg) {sem_wait(mutex);Write(arg);sem_post(mutex);return NULL;
}void *Read2(void *arg) {sem_wait(full);Read(arg);sem_post(empty);return NULL;
}void *Write2(void *arg) {Write(arg);if (buffer N) {sem_post(full);sem_wait(empty);}return NULL;
}void *Read3(void *arg) {sem_wait(full);sem_wait(mutex);Read(arg);sem_post(mutex);sem_post(empty);return NULL;
}void *Write3(void *arg) {sem_wait(mutex);Write(arg);sem_post(mutex);if (buffer N) {sem_post(full);sem_wait(empty);}return NULL;
}void all_sem_init() {// init semint res 0;if (sem_init(read_sem, 0, 1) 0) {printf(failed to init read_sem);res -1;}if (sem_init(write_sem, 0, 1) 0) {printf(failed to init write_sem);res -1;}if (sem_init(mutex, 0, 1) 0) {printf(failed to init mutex);res -1;}if (sem_init(full, 0, 0) 0) {printf(failed to init full);res -1;}if (sem_init(empty, 0, 0) 0) {printf(failed to init empty);res -1;}if (res)exit(0);
}void all_sem_des() {// destroy semsem_destroy(read_sem);sem_destroy(write_sem);sem_destroy(mutex);sem_destroy(full);sem_destroy(empty);
}int main(int argc, char *argv[]) {srand(888);int res 0;int randm 0;void *(*target)(void *) NULL;pthread_t myThreads[MAX_PROCESS_NUM];all_sem_init();for (int i 0; i MAX_PROCESS_NUM; i) {randm rand() % 4;if (i % 2) {
// target Read;
// target Read1;
// target Read2;target Read3;} else {
// target Write;
// target Write1;
// target Write2;target Write3;}res pthread_create(myThreads[i], NULL, target, NULL);if (res 0) {printf(failed to create the thread!);exit(0);}sleep(randm);}void *thread_result NULL;for (int i 0; i MAX_PROCESS_NUM; i)res pthread_join(myThreads[i], thread_result);all_sem_des();return 0;
}版权声明原创文章转载请注明出处 ©️ Sylvan Ding 参考文献
Linux系统编程——线程同步与互斥POSIX无名信号量
