我正在学习操作系统的工作原理，从 Raspberry Pi 上的 Linux 开始。目前，我正在编写一个程序，该程序使用 pthread 创建多个线程并相互通信。在这个程序中，将有 2 个线程(如果算上 main() 则为 3 个)，1 个正在写入，另一个正在读取，两个线程都使用公共(public)结构体进行读写，并使用互斥体相互发送信号(通过检查锁，锁定和解锁)。
要检查线程通信，我会执行以下操作: 写入线程将从名为 randStrings.txt 的文件中读取，计算“e”的数量和每行的字符总数，然后将这两个数字放入一个公共(public)结构中。
读取线程将写入一个名为 resultStrings.txt 的文件，从公共(public)结构中读取，然后写入 'e' 的数量(如果 e 计数!= 0)，否则，写入 '-' 的总长度那条线。
到目前为止，我的线程可以相互通信，但是，我无法执行 pthread_join() 在 2 个线程之间来回切换。
这是我的代码:
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <string.h>
#include <unistd.h>
/*
The following structure contains the necessary information
to allow the function "dotprod" to access its input data and
place its output into the structure.
*/
typedef struct
{
int e; //number of e
int c; //number of character
} DOTDATA;
/* Define globally accessible variables and a mutex */
#define NUMTHRDS 1
DOTDATA dotstr;
pthread_t callThd[NUMTHRDS];
//Initialize mutex
pthread_mutex_t mutex_write = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mutex_read = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mutex_critical = PTHREAD_MUTEX_INITIALIZER;
void *writeMutex(void *arg)
{
int count;
int e_count;
int term_sig;
FILE *readf;
char my_lines[100];
char ch;
signed int numbers[2];
int i;
char s[50];
term_sig = -1;
//unlock write region
printf("Write thread: Unlocking write mutex\n");
pthread_mutex_unlock (&mutex_write);
//unlock critical region
printf("Write thread: Unlocking critical mutex\n");
pthread_mutex_unlock (&mutex_critical);
readf = fopen("randStrings.txt", "r");
if (readf == NULL){
printf("Error opening file");
}
//Read the file
while ((fgets(my_lines, 33, readf))!=NULL)
{
e_count = 0;
count = 0;
my_lines[sizeof(my_lines) - 1] = '\0';
printf("%s\n", my_lines);
for (i = 0; i < sizeof(my_lines); i++){
if(my_lines[i] == '\0') break;
else if (my_lines[i]=='e'){
e_count++;
}
else{ //if (my_lines[i] >= 'a' && my_lines[i] <= 'z'){
count++;
}
}
//lock write
printf("Write thread: Locking write mutex\n");
while(pthread_mutex_lock (&mutex_write)!=0)
{
printf("Write thread: Locking write mutex\n");
}
//lock critical region
printf("Write thread: Locking critical mutex\n");
while(pthread_mutex_lock (&mutex_critical)!=0)
{
printf("Write thread: Locking critical mutex\n");
}
printf("Write thread: Writing value\n");
//write to global varibales
dotstr.e = e_count;
dotstr.c = count;
//unlock critical region
printf("Write thread: Unlocking critical mutex\n");
pthread_mutex_unlock (&mutex_critical);
//unlock read
printf("Write thread: Unlocking read mutex\n");
pthread_mutex_unlock (&mutex_read);
printf("\nParent(%d) send value: [%d, %d]\n", getpid(), e_count, count);
printf("Joining thread!\n");
if((pthread_join(callThd[1], NULL)) !=0)
{
printf("Error joining with reading thread!\n");
}
}
fclose(readf);
//lock write
printf("Write thread: Locking write, end signal, mutex\n");
while(pthread_mutex_lock (&mutex_write)!=0)
{
printf("Write thread: Locking write, end signal, mutex\n");
}
//lock critical region
printf("Write thread: Locking critical, end signal, mutex\n");
while(pthread_mutex_lock (&mutex_critical)!=0)
{
printf("Write thread: Locking critical, end signal, mutex\n");
}
printf("Read thread: reading value\n");
//write to global variables
dotstr.e = term_sig;
dotstr.c = term_sig;
//unlock critical region
printf("Write thread: Unlocking critical, end signal, mutex\n");
pthread_mutex_unlock (&mutex_critical);
//unlock read
printf("Write thread: Unlocking read, end signal, mutex\n");
pthread_mutex_unlock (&mutex_read);
pthread_exit(NULL);
}
void *readMutex(void *arg)
{
char readBuffer[1000];
FILE *readf1;
int numbers_e;
int numbers_c;
int sig;
int j;
sig--;
//open the result file.
readf1 = fopen("resultStrings.txt", "w");
while(numbers_e != sig && numbers_c != sig)
{
//unlock read
printf("Read thread: Unlocking read mutex\n");
pthread_mutex_unlock (&mutex_read);
//lock read
printf("Read thread: Locking read mutex\n");
while(pthread_mutex_lock (&mutex_read)!=0)
{
printf("Read thread: Locking read mutex\n");
}
//lock critical region
printf("Read thread: Locking critical mutex\n");
while(pthread_mutex_lock (&mutex_critical)!=0)
{
printf("Read thread: Locking critical mutex\n");
}
printf("Read thread: Reading value\n");
//read global varibales
numbers_e = dotstr.e;
numbers_c = dotstr.c;
//unlock critical region
printf("Read thread: Unlocking critical mutex\n");
pthread_mutex_unlock (&mutex_critical);
//unlock read
printf("Read thread: Unlocking write mutex\n");
pthread_mutex_unlock (&mutex_write);
readBuffer[0] = 0; //reset readBuffer
//Un-bundling data
printf("\nConsumer (%d) Bundle received: [%i, %i]\n", getpid(), numbers_e, numbers_c);
//readBuffer[0] = 0;
if(numbers_e!= 0) {
for (j = 0; j < numbers_e; j++){
readBuffer[j] = 'e';
}
readBuffer[j+1] = '\0';
for (j = 0; j < sizeof(readBuffer); j++) {
if (readBuffer[j] == 'e'){
fprintf(readf1, "%c", readBuffer[j]);
printf("%c", readBuffer[j]);
}
}
fprintf(readf1, "\n");
printf("\n\n");
}
else if(numbers_c != 0) {
for (j = 0; j < numbers_c; j++){
readBuffer[j] = '-';
}
readBuffer[j+1] = '\0';
for (j = 0; j < sizeof(readBuffer) - 1; j++) {
if (readBuffer[j] == '-'){
fprintf(readf1, "%c", readBuffer[j]);
printf("%c", readBuffer[j]);
}
}
fprintf(readf1, "\n");
printf("\n");
}
if((pthread_join(callThd[0], NULL)) !=0)
{
printf("Error joining with writing thread!\n");
}
}
fclose(readf1);
pthread_exit(NULL);
}
// Main program
int main (int argc, char *argv[])
{
//other variables
pthread_attr_t attr;
void *status;
printf("Locking all mutexes...\n");
pthread_mutex_lock (&mutex_read);
pthread_mutex_lock (&mutex_critical);
pthread_mutex_lock (&mutex_write);
//Threads attribute
pthread_attr_init(&attr);
//pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
//Create threads
printf("Creating writing thread...\n");
pthread_create(&callThd[1], &attr, readMutex, NULL);
pthread_create(&callThd[0], &attr, writeMutex, NULL);
printf("Creating reading thread...\n");
for(;;){
}
printf("Program finished, deleting all mutexes...\n");
pthread_mutex_destroy(&mutex_write);
pthread_mutex_destroy(&mutex_read);
pthread_mutex_destroy(&mutex_critical);
pthread_exit(NULL);
}
输出:
Locking all mutexes...
Creating writing thread...
Creating reading thread...
Write thread: Unlocking write mutex
Write thread: Unlocking critical mutex
kuuxfithomqjnyxqsdpagdue
Write thread: Locking write mutex
Write thread: Locking critical mutex
Write thread: Writing value
Write thread: Unlocking critical mutex
Write thread: Unlocking read mutex
Parent(2917) send value: [1, 24]
Read thread: Unlocking read mutex
Read thread: Locking read mutex
Read thread: Locking critical mutex
Read thread: Reading value
Read thread: Unlocking critical mutex
Read thread: Unlocking write mutex
Consumer (2917) Bundle received: [1, 24]
e
Joining thread!
Error joining with reading thread!
czfnvphqnmzhunukxhjvxbyncerxjba
Write thread: Locking write mutex
Write thread: Locking critical mutex
Write thread: Writing value
Write thread: Unlocking critical mutex
Write thread: Unlocking read mutex
Parent(2917) send value: [1, 31]
Joining thread!
Error joining with reading thread!
gzxwgojtnrnblyyshtqjrelwvif
Write thread: Locking write mutex
^C
编辑2: 感谢达伦指出我的错误。通过在我不需要的地方使用指针，他们弄乱了我的结果。
现在我发现了另一个问题，当使用 pthread_join() 在两个线程之间来回跳转时，它只能跳转一次。读取线程已完成处理来自写入线程的数据，并且写入线程仍然有更多数据要发送，但它永远不能再次调用读取线程来执行此操作。有没有办法可以在两个线程之间来回切换？也许有一种更简单的方法可以在不使用 pthread_join() 的情况下执行此操作？
另外，当两个线程完成工作后如何停止程序？现在，我必须在 main 中放置一个无限循环，以保持它们运行，而不会在线程完成之前销毁所有互斥体，但除了 CTRL + C 之外，没有办法阻止它们。
最佳答案
当您确实不需要它们时，您创建了很多指针(“*”字符)。您似乎不知道它们的用途...如果您将某些内容用作数字，只需使用“int”，而不是“int *”...
关于c - 线程间通信，线程之间的切换，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/19614086/