C language, how I love it

I quite enjoy working with multiple threads to speed up a program. I recently wrote (what I considered) a high-performace timer which read commands in from a named pipe. This afforded the user the ability to script/program around my program as they please. I intend to put header files with all my #define statements so other programs can use it effectively.

POSIX Threads, or pthreads, is technically a language-independent execution model for multi-threading a program, but here I refer to the implementation of said model in C’s standard library.

The biggest nuisance with pthread is casting and packing all the parameters up into a void *:

static void main(int argc, char * argv[])
{
    ...
    // parameter packing
    void * read_packed[3] = {(void *) &timer, (void *) pipe_path, (void *) &print_pipe[1]};
    void * print_packed[3] = {(void *) &timer, (void *) stdout, (void *) &print_pipe[0]};
    ...
    pthread_create(&read_thread, NULL, read_loop, read_packed);
    pthread_create(&print_thread, NULL, print_loop, print_packed);
    ...

Then these parameters need be unpacked in the same way:

void * read_loop(void * param)
{
    // parameter unpacking
    void * * packed = (void * *) param;
    Timer * timer = (Timer *) packed[0];
    char * fifo_path = (char *) packed[1];
    int * print_command_pipe = (int *) packed[2];
    ...

void * print_loop(void * param)
{
    // parameter unpacking
    void * * packed = (void * *) param;
    Timer * timer = (Timer *) packed[0];
    FILE * print_to = (FILE *) packed[1];
    int * pipe = (int *) packed[2];
    ...

This is required because the pthread standard requires threads to share the heap with the main thread, but completely segregates each thread’s stack. So to start a thread with certain data, a pointer to where that data is in the stack is required.