C-將多線程程序編寫為平方數

Question

我正在嘗試編寫一個程序，該程序使用多個線程來計算1-10000之間的數字平方。 我試圖使每個線程一次平方一個數字，最多8個線程。 這意味着線程1-8將對8個數字求平方，並在完成時開始對下一個數字進行平方等。

我的代碼編譯沒有錯誤，但是沒有將任何內容輸出到輸出文件。 我無法確切指出問題所在，所以有人可以給我一些提示或為我指明正確的方向嗎？

另外，對於那些提供代碼幫助的人，我評論了一些內容，我不希望對其進行更改。 我仍然懷疑它們是否仍然需要，但是我將它們用於該項目的其他部分，並希望保持它們不變。 謝謝。 這是我的代碼：

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <pthread.h>

#define NUMBER_OF_THREADS 8
#define START_NUMBER 1
#define END_NUMBER 10000

FILE *f;

void *sqrtfunc(void *tid) { //function for computing squares
    int i;
    for (i = START_NUMBER; i<=END_NUMBER; i++){
        fprintf(f, "%lu squared = %lu\n", i, i*i);
    }
}

int main(){
    //Do not modify starting here
    struct timeval start_time, end_time;
    gettimeofday(&start_time, 0);
    long unsigned i;
    f = fopen("./squared_numbers.txt", "w");
    //Do not modify ending here

    pthread_t mythreads[NUMBER_OF_THREADS]; //thread variable
    long mystatus;

    for (i = 0; i < NUMBER_OF_THREADS; i++){ //loop to create 8 threads
        mystatus = pthread_create(&mythreads[i], NULL, sqrtfunc, (void *)i);
        if (mystatus != 0){ //check if pthread_create worked
            printf("pthread_create failed\n");
            exit(-1);
        }
    }
    for (i = 0; i < NUMBER_OF_THREADS; i++){
        if(pthread_join(mythreads[i], NULL)){
            printf("Thread failed\n");
        }
    }
    exit(1);

    //Do not modify starting here
    fclose(f);
    gettimeofday(&end_time, 0);
    float elapsed = (end_time.tv_sec-start_time.tv_sec) * 1000.0f + \
                    (end_time.tv_usec-start_time.tv_usec) / 1000.0f;
    printf("took %0.2f milliseconds\n", elapsed);
    //Do not modify ending here
}

我能想到的唯一解決方案是移動創建8個線程的for循環並將其放置在sqrtfunc函數的for循環內。 這行得通嗎？ 提前致謝。

Answer 1

為了避免線程爭用文件訪問的問題，每個線程都可以返回結果，該結果將由主進程放入文件中。 否則線程可以准備結果字符串並鎖定，然后僅將這個字符串寫入文件。 下面是第一個解決方案

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <pthread.h>

#define NUMBER_OF_THREADS 8
#define START_NUMBER 1
#define END_NUMBER 1000

FILE* f;

struct Thread_argument
{
    unsigned long long start;
    int range;
};

void* sqrtfunc( void* a ) //function for computing squares
{
    struct Thread_argument* argument = ( struct Thread_argument* )a;
    unsigned long long* result = calloc( argument->range, sizeof( unsigned long long ) );

    for( int i = 0; i < argument->range; i++ )
    {
        result[i] = ( argument->start + i ) * ( argument->start + i );
    }

    free( a );
    return result;
}

int main()
{
    //Do not modify starting here
    struct timeval start_time, end_time;
    gettimeofday( &start_time, 0 );
    long unsigned i;
    f = fopen( "./squared_numbers.txt", "w" );
    //Do not modify ending here
    pthread_t mythreads[NUMBER_OF_THREADS]; //thread variable
    long mystatus;
    int END = END_NUMBER + 1;
    int const range = ( END - START_NUMBER ) / ( NUMBER_OF_THREADS - 1 );

    for( int i = 0; i < NUMBER_OF_THREADS; i++ ) //loop to create 8 threads
    {
        struct Thread_argument* ta = malloc( sizeof( struct Thread_argument ) );
        ta->start = i * range + START_NUMBER;
        ta->range = range;

        if( i == NUMBER_OF_THREADS - 1 )
        {
            ta->range = ( END - START_NUMBER ) % ( NUMBER_OF_THREADS - 1 );
        }

        mystatus = pthread_create( &mythreads[i], NULL, sqrtfunc, ( void* )ta );

        if( mystatus != 0 ) //check if pthread_create worked
        {
            printf( "pthread_create failed\n" );
            exit( -1 );
        }
    }

    unsigned long long* results[NUMBER_OF_THREADS]; //thread variable

    for( int i = 0; i < NUMBER_OF_THREADS; i++ )
    {
        if( pthread_join( mythreads[i], ( void** )&results[i] ) )
        {
            printf( "Thread failed\n" );
        }
    }

    for( int i = 0; i < NUMBER_OF_THREADS - 1; i++ )
    {
        for( int j = 0; j < range; ++j )
        {
            fprintf( f, "%d %lld\n", i * range + j + START_NUMBER, results[ i ][ j ] );
        }

        free( results[ i ] );
    }

    int leftovers = ( END - START_NUMBER ) % ( NUMBER_OF_THREADS - 1 );

    for( int i = 0; i < leftovers; ++i )
    {
        fprintf( f, "%d %lld\n", ( NUMBER_OF_THREADS - 1 ) * range + i + 1, results[ NUMBER_OF_THREADS - 1 ][ i ] );
    }

    free( results[ NUMBER_OF_THREADS - 1 ] );
    fclose( f );
    //Do not modify starting here
    gettimeofday( &end_time, 0 );
    float elapsed = ( end_time.tv_sec - start_time.tv_sec ) * 1000.0f + \
                    ( end_time.tv_usec - start_time.tv_usec ) / 1000.0f;
    printf( "took %0.2f milliseconds\n", elapsed );
    //Do not modify ending here
    return 0;
}