[英]Cat unix command multithread implementation
嗨,我正在嘗試實施比提供的更快的cat。
我當前的實現如下所示:
#include <pthread.h>
#include <stdlib.h>
#include <stdio.h>
#define BUF_SIZE 1024*1024*1024
char buffer[BUF_SIZE];
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond_var = PTHREAD_COND_INITIALIZER;
pthread_cond_t cond_var2 = PTHREAD_COND_INITIALIZER;
int readed = 0;
/*
Read characters from standard input and saves them to buffer
*/
void *consumer(void *data) {
int r;
while(1) {
//---------CRITICAL CODE--------------
//------------REGION------------------
pthread_mutex_lock(&mutex);
if (readed > 0)
{
pthread_cond_wait(&cond_var2, &mutex);
}
r = read(0, buffer, BUF_SIZE);
readed = r;
pthread_cond_signal(&cond_var);
pthread_mutex_unlock(&mutex);
//------------------------------------
if (r == -1){
printf("Error reading\n");
}
else if (r == 0) {
pthread_exit(NULL);
}
}
}
/*
Print chars readed by consumer from standard input to standard output
*/
void *out_producer(void *data) {
int w;
while(1){
//---------CRITICAL CODE--------------
//-------------REGION-----------------
pthread_mutex_lock(&mutex);
if (readed == 0)
{
pthread_cond_wait(&cond_var, &mutex);
}
w = write(1, buffer, readed);
readed = 0;
pthread_cond_signal(&cond_var2);
pthread_mutex_unlock(&mutex);
//------------------------------------
if (w == -1){
printf("Error writing\n");
}
else if (w == 0) {
pthread_exit(NULL);
}
}
}
您會提出什么建議以使其更快? 有任何想法嗎? 我在考慮BUF_SIZE,您認為最佳緩沖區大小是什么?
Main只是使線程:
int main() {
// Program RETURN value
int return_value = 0;
// in - INPUT thread
// out - OUTPUT thread
pthread_t in, out;
// Creating in thread - should read from standard input (0)
return_value = pthread_create(&in , NULL, consumer, NULL);
if (return_value != 0) {
printf("Error creating input thread exiting with code error: %d\n", return_value);
return return_value;
}
// Creating out thread - should write to standard output (1)
return_value = pthread_create(&out, NULL, out_producer, NULL);
if (return_value != 0) {
printf("Error creating output thread exiting with code error: %d\n", return_value);
return return_value;
}
return_value = pthread_join(in, NULL);
return_value = pthread_join(out, NULL);
return return_value;
}
為cat
添加線程的精確度如何使其更快? 您不能只是在任何程序上拋出並行性,並期望它運行得更快。
Cat基本上只是將輸入的每一行(通常是從文件中)傳輸到輸出。 由於線條的順序很重要,因此必須使用互斥來避免競爭。
並行速度的上限( cat
可以運行的最快速度)不能高於串行的cat
,因為每個線程都必須執行串行操作以及同步的開銷。
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