c# Parallel.For 并行编程 执行顺序测试

 因为有个for 实际执行结果尽管是按照for里边的顺序执行,但处理器让哪个分线程先执行,谁先处理完就不一定了.

对于要求结果需要先后顺序的,比如对text内容的操作, 用并行 Parallel.For 操作,不做进一步优化处理,那结果就不是想要的了,还要l用它的并行的功能所以要多程序进行改进,

我使用的做法是初始化buffer list 把list数组的顺序定下来,在循环中,把对应的值顺序赋值给list.    这样做可能写的有点死,根据实际应用调整启动循环的数量实际运行起来效果不错.

做了个简单的测试,同时赋值多个字符串,打印list字符串的值,

 string a = "sssssssssssssssssssssssssssssssssssssssssss";
            string b = "jjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjj";
            string c = "nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnmmm";
            string d = "ssssssssssssssssssssssssssssssssssssssssssssssssss";
            string o = "hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh";
            string f = "ttttttttttttttttttttttttttttttttttttttttttttttttttt";
            List<string> la = new List<string>();
            la.Add(a);
            la.Add(b);
            la.Add(c);
            la.Add(d);
            la.Add(o);
            la.Add(f);
            Parallel.For(0, 6 /*portion*/, (i, ParallelLoopState) =>
            {
              Console.WriteLine(la[i]) ;
            });

结果:

顺序大变

再运行一次

因为设置断点,程序停了一会显示按照先后了

 在运行一次,去掉断点

总结:对需要先后顺序的操作明显满足不了

本来已经加上一下代码就可以了

                  if (i == 0)
                         {
                             using (mmf_reader = mmf.CreateViewAccessor(0, portion1, MemoryMappedFileAccess.Read))
                             {
                                 buffer = new byte[portion1];

                                 mmf_reader.ReadArray(0, buffer, 0, (int)portion1);
                                 mappedFiles.Add(new MappedFile
                                 {
                                     Offset =/* i **/ portion1, //fileOffset,  
                                    Buffer = buffer,
                                     FileSize = portion1
                                 });
                             }
                         }
                         else if (i == 1)
                         {
                             using (mmf_reader = mmf.CreateViewAccessor(portion1, portion2 - portion1, MemoryMappedFileAccess.Read))
                             {
                                 buffer = new byte[portion2 - portion1];

                                 mmf_reader.ReadArray(0, buffer, 0, (int)(portion2 - portion1));
                                 mappedFiles.Add(new MappedFile
                                 {
                                     Offset = portion1 + portion2,// i * portionSize, //fileOffset,  
                                    Buffer = buffer,
                                     FileSize = portion2 - portion1
                                 });
                             }
                         }
                         else if (i == 2)
                         {
                             using (mmf_reader = mmf.CreateViewAccessor(portion2, portion3 - portion2, MemoryMappedFileAccess.Read))
                             {
                                 buffer = new byte[portion3 - portion2];

                                 mmf_reader.ReadArray(0, buffer, 0, (int)(portion3 - portion2));
                                 mappedFiles.Add(new MappedFile
                                 {
                                     Offset = portion3 + portion2,// i * portionSize, //fileOffset,  
                                    Buffer = buffer,
                                     FileSize = portion3 - portion2
                                 });
                             }
                         }
                         else if (i == 3)
                         {
                             using (mmf_reader = mmf.CreateViewAccessor(portion2, portion3 - portion2, MemoryMappedFileAccess.Read))
                             {
                                 buffer = new byte[portion3 - portion2];

                                 mmf_reader.ReadArray(0, buffer, 0, (int)(portion3 - portion2));
                                 mappedFiles.Add(new MappedFile
                                 {
                                     Offset = portion3 + portion2,// i * portionSize, //fileOffset,  
                                    Buffer = buffer,
                                     FileSize = portion3 - portion2
                                 });
                             }
                         }
                         else if (i == 4)
                         {
                             using (mmf_reader = mmf.CreateViewAccessor(portion3, portion4 - portion3, MemoryMappedFileAccess.Read))
                             {
                                 buffer = new byte[portion4 - portion3];

                                 mmf_reader.ReadArray(0, buffer, 0, (int)(portion4 - portion3));
                                 mappedFiles.Add(new MappedFile
                                 {
                                     Offset = portion3 + portion2,// i * portionSize, //fileOffset,  
                                    Buffer = buffer,
                                     FileSize = portion4 - portion3
                                 });
                             }
                         }
                         else if (i == 5)
                         {
                             using (mmf_reader = mmf.CreateViewAccessor(portion4, portion5 - portion4, MemoryMappedFileAccess.Read))
                             {
                                 buffer = new byte[portion5 - portion4];

                                 mmf_reader.ReadArray(0, buffer, 0, (int)(portion5 - portion4));
                                 mappedFiles.Add(new MappedFile
                                 {
                                     Offset = portion3 + portion2,// i * portionSize, //fileOffset,  
                                    Buffer = buffer,
                                     FileSize = portion5 - portion4
                                 });
                             }
                         }
                    }

 以上尽管值加进去了,里边顺序还是变了并行线程用起来还是有些复杂度的,

对以上

mappedFiles 先初始化 ,

 mappedFiles = new List<MappedFile>();
            //初始化 list 六个
            for (int i = 0; i < 6; i++)
            {
                MappedFile map = new MappedFile();
                mappedFiles.Add(map);

mappedFiles[0]=new MappedFile
{
// Offset =/* i **/ portion1, //fileOffset, 
Buffer = buffer,
// FileSize = portion1
};  

不用list.add的方式,直接赋值方式.问题解决