Managing memory in Windows prior to Win32 involved a great deal of uncertainty about using the C run-time (CRT) library. With Win32 there should be little hesitation. The CRT library in Win32 is implemented in a manner similar to FIXED memory allocated via the local and global memory management functions. The CRT library is also implemented using the same default heap manager as the global and local memory management functions.
Subsequent memory allocations via malloc, GlobalAlloc, and LocalAlloc return pointers to memory allocated from the same heap. The heap manager does not divide its space among the CRT and global/local memory functions, and it does not maintain separate heaps for these functions. Instead, it treats them the same, promoting consistent behavior across the types of functions. As a result, you can now write code using the functions you're most comfortable with. And, if you're interested in portability, you can safely use the CRT functions exclusively for managing heap memory. Summary and Recommendations Heap memory management in Win32 is greatly improved over past versions of Windows. Instead of a systemwide global heap and application-specific local heaps, each application in Win32 has a default heap and as many dynamic heaps as the application wants to create. Both types of heaps can grow dynamically and use as much of the address space as they need to satisfy an allocation request. The default heap provides all dynamic memory allocations for the C run-time library malloc functions as well as the global and local memory functions. The heap memory functions can also allocate from the default heap by using its handle, which they retrieve by calling the GetProcessHeap function. The dynamic heap provides serialization to avoid conflict among multiple threads accessing the same heap. To support the management of multiple dynamic heaps, each heap is identified by a unique handle returned by the HeapCreate function. Heaps do at least one thing well—they allocate smaller chunks of memory rather quickly. So whenever you are reluctant to create an automatic variable in a window procedure simply for an occasional LoadString buffer, why not use GlobalAlloc or LocalAlloc, malloc or HeapAlloc? Heaps are also very good at allocating storage for dynamic data structures. Dynamic heaps lend themselves particularly well to managing several distinct dynamic data structures in an application. Finally, what is the cost of using a heap? Well, if you never use any MOVEABLE (including DISCARDABLE) memory, the cost is considerably lower, and MOVEABLE memory probably doesn't buy you much in a 32-bit linear address space. Not to mention that at 8 bytes per MOVEABLE memory handle, the system limits processes to 65,535 handles. Each chunk of heap memory allocated in either the default heap or a dynamic heap is subject to a 16-byte granularity and is charged a 16-byte header. In total, then, allocating 1 byte of MOVEABLE memory costs 40 bytes (8 bytes for the handle table entry, 16 bytes for granularity, and 16 bytes for the header). Happy heaping Best regards, Miguel Angel marchuet Patrick Mast escribió: > Hello Miguel, > >>> if you use -DHB_FM_WIN32_ALLOC then uses windows api memory manager >>> in other case you was using -DHB_FM_STD_ALLOC. > > When should we use -DHB_FM_WIN32_ALLOC and when -DHB_FM_STD_ALLOC? > What is the advantage of using -DHB_FM_WIN32_ALLOC? > > Patrick > > ------------------------------------------------------------------------- > This SF.Net email is sponsored by the Moblin Your Move Developer's challenge > Build the coolest Linux based applications with Moblin SDK & win great prizes > Grand prize is a trip for two to an Open Source event anywhere in the world > http://moblin-contest.org/redirect.php?banner_id=100&url=/ > _______________________________________________ > xHarbour-developers mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/xharbour-developers > > __________ Información de ESET NOD32 Antivirus, versión de la base de firmas > de virus 3550 (20081023) __________ > > ESET NOD32 Antivirus ha comprobado este mensaje. > http://www.eset.com > > > ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ xHarbour-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/xharbour-developers
