Write one C program to measure the average time to create a thread using pthread_create() and to create a process using fork().
1. Use a for loop to create 300 threads using pthread_create(), and measure the total time to create these 300 threads. Then compute its average;
2. Use a for loop to create 300 processes using fork(), and measure the total time to create these 300 processes. Then compute its average;
Briefly describe the reasons for the difference in timings.
It needs to use gettimeofday() to retrieve the system time.
Certainly! Here's a C program that measures the average time to create a thread using `pthread_create()` and to create a process using `fork()`, using the `gettimeofday()` function to retrieve the system time:
```c
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <pthread.h>
#include <unistd.h>
#include <sys/wait.h>
#define NUM_THREADS 300
void *threadFunc(void *arg) {
// Your thread code
// Exit thread
pthread_exit(NULL);
}
int main() {
struct timeval tvalBefore, tvalAfter;
long int totalThreadTime = 0;
long int totalProcessTime = 0;
// Measure time for creating threads
for (int i = 0; i < NUM_THREADS; i++) {
gettimeofday(&tvalBefore, NULL);
pthread_t thread;
pthread_create(&thread, NULL, threadFunc, NULL);
pthread_join(thread, NULL);
gettimeofday(&tvalAfter, NULL);
totalThreadTime += (tvalAfter.tv_sec - tvalBefore.tv_sec) * 1000000 + (tvalAfter.tv_usec - tvalBefore.tv_usec);
}
// Measure time for creating processes
for (int i = 0; i < NUM_THREADS; i++) {
gettimeofday(&tvalBefore, NULL);
pid_t child = fork();
if (child == 0) {
// Child process
exit(0);
} else if (child > 0) {
// Parent process
wait(NULL);
gettimeofday(&tvalAfter, NULL);
totalProcessTime += (tvalAfter.tv_sec - tvalBefore.tv_sec) * 1000000 + (tvalAfter.tv_usec - tvalBefore.tv_usec);
} else {
// Fork failed
printf("Fork failed.\n");
return 1;
}
}
double avgThreadTime = (double)totalThreadTime / NUM_THREADS;
double avgProcessTime = (double)totalProcessTime / NUM_THREADS;
printf("Average time to create a thread: %lf microseconds\n", avgThreadTime);
printf("Average time to create a process: %lf microseconds\n", avgProcessTime);
return 0;
}
```
The program uses a for loop to create 300 threads and measures the total time to create these threads using `pthread_create()`. It also computes the average time by dividing the total time by the number of threads.
Similarly, the program uses a for loop to create 300 processes and measures the total time to create these processes using `fork()`. Again, it computes the average time by dividing the total time by the number of processes.
The `gettimeofday()` function is used to capture the system time before and after the creation of each thread or process. By subtracting the before time from the after time, we get the time taken to create the thread or process in microseconds.
The difference in timings between creating threads and creating processes can be attributed to several factors:
1. Overhead: Creating a thread is generally faster than creating a process because threads are lighter-weight entities. Threads share the same memory space and resources of the parent process, so creating a thread involves less overhead compared to creating an entirely new process.
2. Context Switching: Threads can switch context more efficiently than processes because they share the same memory space. Context switching between threads only requires switching the CPU registers, while context switching between processes involves saving and restoring the entire process's memory space and state.
3. Synchronization: Threads can communicate and synchronize with each other more easily since they share the same memory space. Inter-thread communication is generally faster than inter-process communication, which requires more complex mechanisms such as pipes, sockets, or shared memory.
These factors contribute to the overall difference in timings between creating threads and creating processes. However, it's important to note that the actual timings can vary depending on the system and workload.