利用内存映射文件实现进程间图片轮播
使用共享内存进行多进程通信是最快的IPC(Inter-Process Communication)方式，往往与信号量配合使用，在另一篇文章当中已经展示过相关的代码，但是可用性不高，因为如果需要向内存写入时可以同时读出数据，会导致展示图片数据错乱。与信号量的配合使用则能够解决这个问题。
首先，C++程序作为图片发送端，即向共享内存中写入图片。轮流地打开imageName数组中的图片写入共享内存区域pBuf，pBuf[0]到pBuf[3]作为信号量而保留，图片数据从pBuf[4]开始写。
图片的读取和流程控制在C#进行，流程中仅使用pBuf[0]与pBuf[1]作为信号量，分别表示是否继续读取和是否完成写入。
- pBuf[0]为1表示读取继续进行，若不再需要读取，则置pBuf[0]为0，则C++程序会退出while循环，回收共享内存的资源。
- pBuf[1]为0表示C++程序正在将图片信息写入到内存映射文件，此时C#不应读取其内容，待C++读取完毕置pBuf[1]为1，C#程序则可以开始从内存映射文件中读取数据转换成图片。
将C++程序进行编译，生成应用程序（例如名为readLoop.exe，这需要在C#中指定）然后编写C#的winform工程，并使用BackgroundWorker的多线程方式启动这个应用程序。
#include <cstdio>
#include <cstring>
#include <windows.h>
const char *imageName[] = {
"11683053441969795147.jpg",
"0b3cdd7308f340bead962c992b4b2fd4.jpg",
"18639d5b1f7e40dfbfad6b3bd9c407e9.jpg",
"37d4448ad3f14b48901ff3b90c33eaea.jpg",
"495d3b575da64966b3ca3574c3e2c4ea.jpg",
"589a971d0a7f4814be6926d0076ecaba.jpg",
"678bf3bfa3554393b2b3e784f257325f.jpg",
"a4743b26cf0f46dfaf1f42d06611601c.jpg",
"aaa930ba51e3480c805f8fb82734069b.jpg",
"d9e43b03a7364fb3849cd3ef0cd840fc.jpg",
"dd3801e0bb084537b505ca3fcd301f8e.jpg",
"eac81c422041458c95fb8d8cb31ba1bf.jpg"
};
#define BUF_SIZE 360000
const char szName[] = "fm01";
int main(void)
{
char Root[] = "E:\\imgSample\\";
char fileName[50];
int idx = 0,i;
FILE *fp;
HANDLE hMapFile = CreateFileMapping(
INVALID_HANDLE_VALUE,
NULL,
PAGE_READWRITE,
0,
BUF_SIZE,
(LPCSTR)szName
);
char *pBuf = (char*)MapViewOfFile(
hMapFile,
FILE_MAP_ALL_ACCESS,
0,
0,
BUF_SIZE
);
pBuf[0]=1;
while(pBuf[0]==1)
{
printf("p[0]:%d\t",pBuf[0]);
strcpy(fileName,Root);
strcat(fileName,imageName[idx]);
idx++;
if(idx>11)
{
idx=0;
}
printf("%s\n",fileName);
fp = fopen(fileName,"rb");
pBuf[1]=0;
i=4;
while(fscanf(fp,"%c",&pBuf[i])!=EOF)
{
i++;
}
pBuf[i]=0;
pBuf[1]=1;
Sleep(50);
fclose(fp);
}
UnmapViewOfFile(pBuf);
CloseHandle(hMapFile);
printf("end\n");
return 0;
}using System;
using System.Drawing;
using System.Windows.Forms;
using System.IO;
using System.IO.MemoryMappedFiles;
using System.Runtime.InteropServices;
using System.Threading;
using System.ComponentModel;
using System.Diagnostics;
namespace client_csharp
{
public partial class Form1 : Form
{
const int BUF_SIZE = 360000;
BackgroundWorker bg1;
Image pic,lastPic;
int frameCount;
byte[] charsInMMf;
public Form1()
{
InitializeComponent();
bg1 = new BackgroundWorker();
bg1.WorkerReportsProgress = true;
bg1.WorkerSupportsCancellation = true;
bg1.DoWork += new DoWorkEventHandler(doworks);
bg1.RunWorkerCompleted += new RunWorkerCompletedEventHandler(runcomplete);
bg1.ProgressChanged += new ProgressChangedEventHandler(progresschanged);
}
private void doworks(Object sender,DoWorkEventArgs args)
{
Process p = new Process();
p.StartInfo.FileName = "readLoop.exe";
p.StartInfo.UseShellExecute = false;
p.StartInfo.CreateNoWindow = true;
p.StartInfo.RedirectStandardError = true;
p.StartInfo.RedirectStandardOutput = true;
p.Start();
lastPic = null;
waitForOpenFm();
flush(sender as BackgroundWorker);
}
private void waitForOpenFm()
{
while (true)
{
try
{
MemoryMappedFile.OpenExisting("fm01");
break;
}
catch
{
// still not open
Thread.Sleep(50);
}
}
return;
}
private void flush(BackgroundWorker worker)
{
using (var mmf = MemoryMappedFile.OpenExisting("fm01"))
{
MemoryMappedViewAccessor viewAccessor = mmf.CreateViewAccessor(0, BUF_SIZE);
charsInMMf = new byte[BUF_SIZE];
frameCount = 0;
while (true)
{
while(true)
{
if (viewAccessor.ReadByte(1)==1)
{
break;
}
Thread.Sleep(10);
}
viewAccessor.ReadArray<byte>(4, charsInMMf, 0, BUF_SIZE);
pic = Image.FromStream(new MemoryStream(charsInMMf));
worker.ReportProgress(0);
frameCount += 1;
if (worker.CancellationPending)
{
viewAccessor.Write(0, 0);
break;
}
Thread.Sleep(50);
}
}
}
private void runcomplete(Object sender, RunWorkerCompletedEventArgs args)
{
}
private void progresschanged(Object sender, ProgressChangedEventArgs args)
{
if(lastPic!=null)
lastPic.Dispose();
pictureBox1.BackgroundImage = pic;
lastPic = pic;
label1.Text = frameCount.ToString();
}
private void button1_Click(object sender, EventArgs e)
{
bg1.RunWorkerAsync();
}
private void button2_Click(object sender, EventArgs e)
{
bg1.CancelAsync();
}
}
}