第六章-OpenMp多线程编程笔记(intel)

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期末考点

6.1
6.10
6.11
6.15
6.18
6.21

6.1

#include <stdio.h>
#include "omp.h"
int main(int argc, char * argv[])
{
	printf("Hello from serial.\n");
	printf("Thread number=%d\n", omp_get_thread_num());
#pragma omp parallel
	{
		printf("Hello from parallel. Thread number=%d，Total number of threads=%d\n", omp_get_thread_num(), omp_get_num_threads());
	}

	printf("The total number of threads = %d\n", omp_get_num_threads());
	printf("Hello from serial again.\n");
	return 0;
}

第六章-OpenMp多线程编程笔记(intel)_#pragma

并行区域多线程并行执行，所以多次执行产生结果不同，每个线程都完整的复制一遍代码执行一遍。

6.10

#include <stdio.h>
#include "omp.h"

int main(int argc,char *argv[])
{
  #pragma omp parallel for
  for (int i = 0;i<5;i++)
  {
    printf("hello world i=%d,The current thread number is %d\n", i, (int)omp_get_thread_num());
  }
  return 0;
}

第六章-OpenMp多线程编程笔记(intel)_#include_02

循环并行化采用工作分配的执行方式，将循环所需要的所有工作量按照一定的方式分配到各个执行线程中，其工作量与串行工作量一致

6.11

#include <stdio.h>
int counter = 0; 
#pragma omp threadprivate(counter) //using threadprivate

void inc_counter()
{
	counter++;
}

int main(int argc, char* argv[])
{
#pragma omp parallel
	for (int i = 0;i<100000000;i++)
	{
		inc_counter();
	}
	printf("counter=%d\n", counter);
    //printf("counter=%d,The current thread number is %d\n",counter,omp_get_thread_num());
	return 0;
}

第六章-OpenMp多线程编程笔记(intel)_多线程_03

结果恒定

若将程序第三行注释掉的话，下面的例子

#include <stdio.h>
int counter = 0; 
//#pragma omp threadprivate(counter) //using threadprivate

void inc_counter()
{
	counter++;
}

int main(int argc, char* argv[])
{
#pragma omp parallel
	for (int i = 0;i<100000000;i++)
	{
		inc_counter();
	}
	printf("counter=%d\n", counter);
    //printf("counter=%d,The current thread number is %d\n",counter,omp_get_thread_num());
	return 0;
}

第六章-OpenMp多线程编程笔记(intel)_多线程_04

结果未定

6.15

#include <stdio.h>
#include "omp.h"
int main(int argc,char *argv[])
{
  #pragma omp parallel
  {
    printf("outside loop thread=%d\n", omp_get_thread_num());
    #pragma omp for
    for (int i = 0;i<3;i++)
    {
      printf("inside loop i=%d thread =%d\n", i, omp_get_thread_num());
    }
  }
  return 0;
}

第六章-OpenMp多线程编程笔记(intel)_#pragma_05

尽管创建的线程数改变了，但是循环次数还是跟按照串行执行次数一致。只不过循环的所有任务被各个线程分别完成。

6.18

#include <stdio.h>
#include "omp.h"

long long counter = 0;
int main(int argc,char *argv[])
{
  #pragma omp parallel
  {
    for (int i = 0; i < 10000000;i++)
	    //#pragma omp atomic //atomic operation
	    counter++;
  }
  printf("counter=%lld\n", counter);
  return 0;
}

第六章-OpenMp多线程编程笔记(intel)_#include_06

使用了锁机制，所以输出等于循环次数*创建的线程数,若将锁机制去掉，结果不确定。

6.21

#include <stdio.h>
#include "omp.h"
void initialization()
{
  int counter = 0;
  printf("thread %d start initialization\n", omp_get_thread_num());
  for (int i = 0;i<100000;i++)
  {
    counter++;
  }
  printf("thread %d finish initialization\n", omp_get_thread_num());
}
void process()
{
  int counter = 0;
  printf("thread %d start process\n", omp_get_thread_num());
  for (int i = 0;i<100000;i++)
  {
    counter += i;
  }
  printf("thread %d finish process\n", omp_get_thread_num());
}
int main(int argc,char *argv[])
{
  #pragma omp parallel
  {
    initialization();
    #pragma omp barrier
    process();    
  }
  return 0;
}

第六章-OpenMp多线程编程笔记(intel)_并发编程_07