问题描述
我有两个类似codeS。
I've got two similar codes.
首先
#pragma omp parallel for shared(g) private(i) schedule(dynamic,1)
for(i=(*g).actualNumberOfChromosomes;i<(*g).maxNumberOfChromosomes;i++)
{
AddCrossoverChromosome(g,i); // it doesnt change actualNumberOfChromosomes
#pragma omp atomic
(*g).actualNumberOfChromosomes++;
}
二
#pragma omp parallel for shared(g) private(i) schedule(static,1)
for(i=(*g).actualNumberOfChromosomes;i<(*g).maxNumberOfChromosomes;i++)
{
AddCrossoverChromosome(g,i); // it doesnt change actualNumberOfChromosomes
#pragma omp atomic
(*g).actualNumberOfChromosomes++;
}
唯一的区别是在第一行。首先code正常工作，但第二个崩溃。
问题是为什么？问题是在某处actualNumberOfChromosomes，但我想知道为什么，而不是仅仅解决这个问题。我可以通过创建另外变量p，并把它分配actualNumberOfChromosomes和改变的循环，所以我等于P，在这种情况下解决这个既codeS做工精细。
The only difference is in first line. First code works fine, but the second one crashes.The question is why?? Problem is somewhere in actualNumberOfChromosomes, but I would like to understand why, and not just solve this. I could solve this by creating addition variable p and assigning actualNumberOfChromosomes to it and changing the loop so i was equal to p, in such case both codes work fine.
推荐答案
的问题是，这个code未OpenMP的符合和不符合的程序有未指定行为。如果你看一下OpenMP API的V3.0规范，部分2.5.1循环结构，说明其下规定：
The problem is that this code is not OpenMP compliant and non-compliant programs have "unspecified" behavior. If you look at the OpenMP API V3.0 spec, section 2.5.1 Loop Construct, under the description it states:
每个相关循环迭代计数条目到最外面的前计算
循环。如果任何相关的循环的执行改变任何用于计算的值的
任何循环计数则行为是不确定的。
日程类型的静态和动态之间的最大区别，就是用静态的，块可有些计算和编译过程中定线程，同时具有动态它在运行时（需要更多的锁）就完成了。
The big difference between a schedule type of static and dynamic, is that with static, the chunks can be somewhat computed and scheduled to threads during compilation, while with dynamic it is done during run-time (requiring more locking).
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