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POC - not reaching proper end with fork(), pipe(), select(), execl(), and write()
 

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  1. POC - not reaching proper end with fork(), pipe(), select(), execl(), and write()
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    <p>I am using forks and pipes to find the amount of 1s and 0s in a string inside of a file. However, I am never reaching the proper end to my program that tallys up the ones and zeroes. It's a pretty small amount of code so here is the whole program:</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; #include &lt;string.h&gt; #include &lt;unistd.h&gt; #include &lt;sys/time.h&gt; int main (int argc, char** argv) { int leftR, rightR; char *string; long size; int recursion = 0; if (argc == 3) { string = argv[1]; size = strlen(string); printf("the string is %s\n", string); if (size &lt;= 2) { int bitCounter[2]; bitCounter[0] = 0; bitCounter[1] = 0; int i; for (i=0; i &lt; size; i++) { if (string[i]=='0') { bitCounter[0]++; } else { bitCounter[1]++; } } write(STDOUT_FILENO, &amp;bitCounter, sizeof(int)*2); printf("read bits, sending back %d ones and %d zeroes\n", bitCounter[1], bitCounter[0]); return 0; } else { recursion = 1; } } if (argc == 2 || recursion) { char *data; if (!recursion) { FILE* filePointer; if ((filePointer = fopen(argv[1], "r")) == NULL) { perror("file didn't work"); } fseek(filePointer, 0, SEEK_END); size = ftell(filePointer); fseek(filePointer, 0, SEEK_SET); data = malloc(size+1); fread(data, size, 1, filePointer); fclose(filePointer); } else { data = malloc(size+1); data = string; } char *right; char *left = malloc((size/2)+1); if (size%2 == 0) { right = malloc(size/2 + 1); } else { right = malloc(size/2 + 2); } memcpy(left, data, size/2); if (size%2 == 0) { memcpy(right, (size/2) + data, size/2); } else { memcpy(right, (size/2) + data, (size/2) + 1); } int pidLeft, pidRight; int leftPipe[2]; int rightPipe[2]; pipe(leftPipe); pipe(rightPipe); fd_set readF; FD_ZERO(&amp;readF); FD_SET(leftPipe[0], &amp;readF); FD_SET(rightPipe[0], &amp;readF); pidLeft = fork(); if (pidLeft &gt; 0) { pidRight = fork(); if (pidRight &gt; 0) { struct timeval timer; timer.tv_sec = 3; timer.tv_usec = 0; close(rightPipe[1]); close(leftPipe[1]); dup2(leftPipe[0], STDOUT_FILENO); dup2(rightPipe[0], STDOUT_FILENO); select(2, &amp;readF, NULL, NULL, &amp;timer); read(leftPipe[0], &amp;leftR, sizeof(int)*2); read(rightPipe[0], &amp;rightR, sizeof(int)*2); printf("going back to parent.\n"); } else if (pidRight == 0) { close(rightPipe[0]); execl("my_program", "my_program", right, "y", NULL); printf("recursion start\n"); exit(1); } } else if (pidLeft == 0) { close(leftPipe[0]); execl("my_program", "my_program", left, "y", NULL); printf("start recursion LEFT\n"); exit(1); } else { fprintf(stderr, "something went wrong! No fork!\n"); } } else { fprintf(stderr, "Please input file name properly\n"); exit(1); } int zeroes = leftR + rightR; int* numOnes[2]; numOnes[0] = &amp;leftR + sizeof(int); numOnes[1] = &amp;rightR + sizeof(int); int ones = (int) *numOnes[0] + (int) *numOnes[1]; printf("0's: %d\n1's: %d\n", zeroes, ones); return 0; } </code></pre> <p>However, the output never reaches my desired end that adds everything up:</p> <pre><code>the string is 01010▒z the string is 010 the string is 0 read bits, sending back 0 ones and 1 zeroes the string is 10▒z the string is 10 read bits, sending back 1 ones and 1 zeroes the string is ▒z read bits, sending back 2 ones and 0 zeroes the string is 10 read bits, sending back 1 ones and 1 zeroes the string is 10100 z the string is 101 the string is 1 read bits, sending back 1 ones and 0 zeroes the string is 01 read bits, sending back 1 ones and 1 zeroes the string is 00 z the string is 00 read bits, sending back 0 ones and 2 zeroes the string is z read bits, sending back 2 ones and 0 zeroes (140) Admin $ </code></pre> <p>A couple quick points to understand the code a little easier:</p> <ul> <li>argc is only 3 when it is being executed within a child</li> <li>children will only read the string if it is less than or equal to 2, otherwise recursively cut the string in half again (and make more children)</li> <li>parents make both a left and right child, both taking half of the string to work on</li> </ul> <p>I guess a couple easy questions to start off would be: </p> <ul> <li>Am I using select() and execl() properly?</li> <li>Am I using read() and write() properly?</li> <li>Is there an exit in the main processes I am missing?</li> <li>Are both children working and using the pipe correctly?</li> <li>(less important) is the strange character in the strings messing up my count? Is that a null terminator somehow inside my string?</li> </ul>
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    1. UStheman
    1. UStheman
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      1. POC - not reaching proper end with fork(), pipe(), select(), execl(), and write()
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      1. VTDownMod
    1. COPlease post code that compiles without errors: `int zeroes = *leftR + *rightR;` generates errors because neither `leftR` nor `rightR` is a pointer. The next line also gets similar complaints.
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      1. POC - not reaching proper end with fork(), pipe(), select(), execl(), and write()
      1. USJonathan Leffler
    2. COFixed, sorry about that.
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      1. POC - not reaching proper end with fork(), pipe(), select(), execl(), and write()
      1. UStheman
    3. CO'Fixed' is not, perhaps, the term I'd use. This code: `int rights = (int) &rightR; int lefts = (int) &leftR; int zeroes = lefts + rights; int ones = (int)(&leftR + sizeof(int)) + (int)(&rightR + sizeof(int));` is extraordinary — and extremely unlikely to be correct. Adding two addresses together yields garbage, not an answer. I'm not sure what you think the `(&leftR + sizeof(int))` is going to yield, but it isn't 'defined behaviour'.
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      1. POC - not reaching proper end with fork(), pipe(), select(), execl(), and write()
      1. USJonathan Leffler
 

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