Utilize POSIX Threads for Concurrency

In single-threaded applications, executing multiple blocking operations (such as disk I/O, network requests, or file downloads) sequentially can make a program painfully slow.

In this challenge, you are provided with a pre-compiled single-threaded program in ~/exercise/download. Your goal is to inspect its execution time, then refactor the code using POSIX Threads (pthreads) so that all file downloads run concurrently.

// ~/exercise/download.c
#include <stdio.h>
#include <unistd.h>

void download_file(const char *filename) {
    printf("Downloading %s...\n", filename);
    sleep(2);  // Simulates network latency
    printf("Finished downloading %s!\n", filename);
}

int main(void) {
    download_file("file1.dat");
    download_file("file2.dat");
    download_file("file3.dat");
    download_file("file4.dat");
    return 0;
}

Task Instructions

1. Observe the Blocking Program: Navigate to ~/exercise and run the provided ./download program with time. Notice how long it takes to download four files sequentially.
2. Refactor using POSIX Threads: Modify download.c (or create a new C file) to execute the file downloads concurrently using POSIX Threads (pthreads).
3. Compile and Verify: Compile your updated code with gcc (remember to link the threads library) and run the resulting executable. Verify that all downloads complete in ~2 seconds instead of the original execution time.