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POHow to Read/Write to a file at the same time with 2 threads?
 

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  1. POHow to Read/Write to a file at the same time with 2 threads?
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    <p>I have a server/client application , with 2 different versions.In the first one client reads a text file and sends text data to the server , and server writes the received data to a new text file("received.txt") ,and when it finishes writing , it prints the text file to screen. </p> <p>In the second version , client does the same thing , but i want the server to print data to screen at the same time it writes on the file "received.txt". You might wonder why am i doing such a thing. I want to speed up the process of writing to the file and printing the file back to the screen. I tought maybe if i use 2 threads , i might speed up the work. </p> <p>I encountered with a problem though , (this is the first time that i use pthreads).Server terminates before it prints the data to the screen.I think it is about scheduling. While newly created thread is running and main thread blocked , the file has nothing to read , and then newly created thread terminates. Thats my guess about the problem. What i want to achieve here is to make this read/write simultenously , if its possible. If i'm doing this all wrong , or i cant make simultenous read/write write with threads , let me know :)</p> <p>Here is the server(second version):</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;sys/types.h&gt; #include &lt;sys/socket.h&gt; #include &lt;netinet/in.h&gt; #include &lt;pthread.h&gt; #include &lt;time.h&gt; void error(char *msg) { perror(msg); exit(1); } //New Thread function void *printData() { FILE *fp = fopen("received.txt" , "r"); char buffer; time_t time1 = time(NULL); if( fp != NULL ) { while( ( buffer = fgetc(fp)) != NULL ) { printf("%c" , buffer); } fclose(fp); } time_t time2 = time(NULL); double diff = difftime(time2 , time1); printf("It took %.lf seconds.\n" , diff); pthread_exit(NULL); } int main(int argc , char *argv[]) { int sockfd , newsockfd , port_no , cli_length , n; char buffer[256]; struct sockaddr_in server_addr , client_addr; FILE *fp; int thread_Created = 0; pthread_t thread; if(argc &lt; 2) { fprintf(stderr , "ERROR , no port provided!"); exit(1); } sockfd = socket(AF_INET , SOCK_STREAM , 0); if( sockfd &lt; 0 ) error("ERROR opening socket."); bzero( (char *) &amp;server_addr , sizeof(server_addr) ); port_no = atoi(argv[1]); server_addr.sin_family = AF_INET; server_addr.sin_port = htons( port_no ); server_addr.sin_addr.s_addr = INADDR_ANY; if( bind( sockfd , (struct sockaddr *) &amp;server_addr , sizeof(server_addr)) &lt; 0 ) { error("ERROR on binding."); } listen(sockfd , 5); cli_length = sizeof(&amp;client_addr); newsockfd = accept( sockfd , (struct sockaddr *) &amp;client_addr , &amp;cli_length ); if (newsockfd &lt; 0 ) error("ERROR on accept."); bzero(buffer , 256); if( (fp = fopen("received.txt" , "w")) != NULL ) { while( (n = read(newsockfd , buffer , 255)) != 0 ) { int i = 0; for(i = 0 ; i &lt; 255 ; i++) { if( buffer[i] != '\0') fputc(buffer[i] , fp); } //Create a new thread to read the file and print the results if( !thread_Created ) { pthread_create( &amp;thread , NULL , printData , NULL ); thread_Created = 1; } } } fclose(fp); /* while(pthread_kill(thread , 0 ) == 0 ) { */ /* } */ } </code></pre>
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    1. USfeluna
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      1. POHow to Read/Write to a file at the same time with 2 threads?
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    1. CODon't read and write a one file at the same time. Use at least a mutex to serialize that. https://computing.llnl.gov/tutorials/pthreads/
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      1. POHow to Read/Write to a file at the same time with 2 threads?
      1. USBasile Starynkevitch
    2. COHmm, i dont know how to use mutexes , i will google it now.
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      1. USfeluna
 

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