Qsharedmemory shared memory for inter-process communication (IPC) and prohibit programs to open

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• 1. Introduction
• 2. Example
• 3. No more open programs

1. Introduction

Very simple library, look directly at the Help document: http://doc.qt.io/qt-5/qsharedmemory.html

Main function: Set Key,create to the system request to establish a memory space, attach current process and memory binding, detach unbind, Lock/unlock sync lock, Data/constdata get memory pointer

Creator process: Setkey,create,attach,lock,data, Operation Data,unlock, no time detach

Visitor: Setkey,attach,lock,data, Operation Data,unlock, not when detach?? No need for create.

• As the creator should be sure that no one else will be able to unbind
• Qsharedmemory destruction is also automatically detach
• One memory space if 0 attach will be destroyed, the data will be gone.
• Read and write operation remember Lock, and be careful not to forget the unlock
• Without the Create key, the call to attach will return false, note that this sentence in the Prohibition program more open useful

Size gets the shared memory, error/errorstring is the error message, and isattached determines whether the current process is bound to memory.

2. Example

Steal a lazy, write together:

2. #include <QCoreApplication>
4. #include <QSharedMemory>
6. #include <QDebug>
8. int main(int argc, char *argv[]) {
10. Qcoreapplication a(argc, argv);
12. //Create a key at the same time, or you can setkey
14. Qsharedmemory sm("test_shared");
16. //If it is the first use you must first create a
18. //The remaining processes do not need to create direct attach
20. if(!sm.Create(1024x768))
22. qdebug()<<"Create Error";
24. Sm.Attach();//bind memory
26. //attach returns BOOL, which can be judged without the following method
28. if(!sm.isattached())
30. qdebug()<<"Attach error";
32. Sm.Lock();
34. int *memdata = static_cast<int*>( sm.Data() ) ;
36. *memdata = 1024x768;
38. Sm.unlock();
40. //So lazy! Want to test a multi-process to build a project under the cuff.
42. Qsharedmemory testsm("test_shared");
44. Testsm. Attach();
46. int *testdata = static_cast<int*>( testsm. Data() );
48. qdebug()<<*testdata;
50. //separates the current process from memory, and automatically calls when the destructor is made
52. Sm.Detach();
54. return A.exec();
56. }

TESTSM will call detach when it is destructor, can Sm.detach (); Put in Qsharedmemory testsm ("test_shared"); You'll see a mistake.

3. No more open programs

2. #include <QCoreApplication>
4. #include <QSharedMemory>
6. int main(int argc, char *argv[]) {
8. Qcoreapplication a(argc, argv);
10. //Create a key at the same time, or you can setkey
12. Qsharedmemory sm("test_shared");
14. if(sm.Attach())
16. return 0;
18. Sm.Create(1);
20. MainWindow W;
22. W.show();
24. return A.exec();
26. }

Very simple principle, as long as there is an open success that will create a 1-size space, follow-up program can be attach and then return ...

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Qsharedmemory shared memory for inter-process communication (IPC) and prohibit programs to open