DLL question

[Lost User]

According to MSDN: Every process that loads the DLL maps it into its virtual address space. After the process loads the DLL into its virtual address, it can call the exported DLL functions. Suppose a process starts and at some stage it dynamically loads a dll. A second process also load the same dll. Now what actually happened ??? Do each of these processes share the same chunk of memory where dll is loaded or dll code is loaded at two different locations for both of these processes ???

[Vimal Earnest]

Yes, the two processes share the same chunk of memory. ~ Vimal

[defrag08]

Vimal Earnest wrote: Yes, the two processes share the same chunk of memory. Suppose the function exposed by the dll has some static variable. Now what happens in this case...whether both applications that are using this dll share single copy of variable ???

[Vimal Earnest]

What happens is, the COW (Copy On Write) mechanism is used by the system to make a private copy of these variables. To be specific, the system makes a private copy of the memory section containing static and global variables in the process modifying these variables. refer chapter 19 (DLL basics) of Jeffrey Richter's Programming Applications for Microsoft Windows 4th ED for more info. ~ Vimal