How to resolve the algorithm Checkpoint synchronization step by step in the C programming language
How to resolve the algorithm Checkpoint synchronization step by step in the C programming language
Table of Contents
Problem Statement
The checkpoint synchronization is a problem of synchronizing multiple tasks. Consider a workshop where several workers (tasks) assembly details of some mechanism. When each of them completes his work they put the details together. There is no store, so a worker who finished its part first must wait for others before starting another one. Putting details together is the checkpoint at which tasks synchronize themselves before going their paths apart. The task Implement checkpoint synchronization in your language. Make sure that the solution is race condition-free. Note that a straightforward solution based on events is exposed to race condition. Let two tasks A and B need to be synchronized at a checkpoint. Each signals its event (EA and EB correspondingly), then waits for the AND-combination of the events (EA&EB) and resets its event. Consider the following scenario: A signals EA first and gets blocked waiting for EA&EB. Then B signals EB and loses the processor. Then A is released (both events are signaled) and resets EA. Now if B returns and enters waiting for EA&EB, it gets lost. When a worker is ready it shall not continue before others finish. A typical implementation bug is when a worker is counted twice within one working cycle causing its premature completion. This happens when the quickest worker serves its cycle two times while the laziest one is lagging behind. If you can, implement workers joining and leaving.
Let's start with the solution:
Step by Step solution about How to resolve the algorithm Checkpoint synchronization step by step in the C programming language
This C code demonstrates the use of OpenMP to parallelize a task, specifically a set of jobs that need to be completed. Let's break down the code step by step to understand its functionality:
-
Header Includes:
#include <stdio.h>
: For input and output operations.#include <stdlib.h>
: For standard library functions likerand
.#include <unistd.h>
: Forusleep
function to introduce a delay.#include <omp.h>
: For OpenMP functions and directives.
-
Main Function:
int main()
: The main entry point of the program.int jobs = 41;
: Initializes the number of jobs to be completed.omp_set_num_threads(5);
: Sets the number of OpenMP threads to 5. This means the program will create five worker threads.
-
OpenMP Parallel Region:
#pragma omp parallel shared(jobs) private(tid)
: Starts an OpenMP parallel region.shared(jobs)
: Thejobs
variable is shared among all threads.private(tid)
: Each thread will have its own copy of thetid
variable.
-
Thread Execution:
- Each thread executes the following code block:
tid = omp_get_thread_num();
: Each thread gets its unique identifier.- Inside the loop, each thread:
- Checks if there are still jobs left (
jobs > 0
). - If there are jobs, it takes one by decrementing
jobs
. - Prints information about taking the job and introduces a delay using
usleep
. - After completing the job, it prints a message indicating completion.
- Checks if there are still jobs left (
- When there are no more jobs, each thread breaks out of the loop.
- Each thread prints a message indicating that it is leaving the parallel region.
- Each thread executes the following code block:
-
Synchronization Barriers:
#pragma omp barrier
: These barriers ensure that all threads reach certain points in the code before proceeding.- The first barrier ensures that all threads have taken jobs or realized that there are no jobs left before continuing.
- The second barrier prevents threads from exiting the parallel region until all jobs are completed.
-
Program Exit:
return 0;
: Themain
function returns 0 to indicate successful program execution.
In summary, this program demonstrates how to use OpenMP to parallelize a task of completing multiple jobs by creating multiple worker threads. The program ensures that all threads have access to the shared jobs
variable while allowing each thread to have its own tid
. Synchronization barriers are used to ensure proper coordination and prevent premature termination of threads.
Source code in the c programming language
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <omp.h>
int main()
{
int jobs = 41, tid;
omp_set_num_threads(5);
#pragma omp parallel shared(jobs) private(tid)
{
tid = omp_get_thread_num();
while (jobs > 0) {
/* this is the checkpoint */
#pragma omp barrier
if (!jobs) break;
printf("%d: taking job %d\n", tid, jobs--);
usleep(100000 + rand() / (double) RAND_MAX * 3000000);
printf("%d: done job\n", tid);
}
printf("[%d] leaving\n", tid);
/* this stops jobless thread from exiting early and killing workers */
#pragma omp barrier
}
return 0;
}
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