Global variables in DLL

For customization dll,（ Non system dll）：

Multiple processes are loaded separately dll when , Because the address space of each process is independent and invisible ,dll The data segment of is one for each process , Global variables do not affect each other .

Multiple threads of the same process multiple times loadlibrary load dll when , for the first time loadlibrary when , The process loads the specified dynamic link library , And map it to the address space used by the current process . The second and later loadlibrary when , Will only affect module Reference count of , The returned image and handle are the same . Of course , The global variable is also the same memory address , In a multithreaded , One change , All visible , Need to be synchronized .

For the system dll, Use the high-order address of the virtual address , The user address space is not visible , The system has been fully loaded when it starts , All processes running under the system have the same global variables .
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