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Top Forums Programming readdir and dynamic array memory corruption Post 302491856 by DreamWarrior on Friday 28th of January 2011 01:14:43 PM
Old 01-28-2011
I'm not convinced on the fragmentation "issue". It may speed things up because you call malloc fewer times, but you'd need to know how your malloc works to know if fragmentation will be an issue. Since most malloc implementations use pools for various sizes anyway, I don't see calling realloc with smaller jumps as bad. Once you call it with a large enough amount to matter then you're in the large pool and either filling in gaps or pushing out the break point.

Though...I suppose on your side, calling malloc with large sizes typically does nothing anyway until the pages are touched...so...it's not as if your calling malloc and asking for a gig (on most operating systems anyway) is going to hurt unless you start actually putting data into the pages "given" to your process when it (inevitably) calls brk.

Either way...it's a blanket statement that one is better than the other. If you had a process that was multi-threaded and read ten million items in with ten threads would you ask for it exponentially in each thread? If you did you would probably regret it, because you'd likely reach the memory limits of a 32 bit process and your mallocs would start failing and you'd have to back down to an additive method at some point.

Anyway, maybe I need to "think on it" some more, but for now I remain unconvinced.

P.S. I'd watch that video...but I don't have Silverlight installed on my Linux machine.
 

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bsdmalloc(3MALLOC)														bsdmalloc(3MALLOC)

NAME
bsdmalloc - memory allocator SYNOPSIS
cc [ flag ... ] file ... -lbsdmalloc [ library ... ] char *malloc(size); unsigned size; int free( ptr); char *ptr; char *realloc( ptr, size); char *ptr; unsigned size; These routines provide a general-purpose memory allocation package. They maintain a table of free blocks for efficient allocation and coa- lescing of free storage. When there is no suitable space already free, the allocation routines call sbrk(2) to get more memory from the system. Each of the allocation routines returns a pointer to space suitably aligned for storage of any type of object. Each returns a null pointer if the request cannot be completed. The malloc() function returns a pointer to a block of at least size bytes, which is appropriately aligned. The free() function releases a previously allocated block. Its argument is a pointer to a block previously allocated by malloc() or real- loc(). The free() function does not set errno. The realloc() function changes the size of the block pointed to by ptr to size bytes and returns a pointer to the (possibly moved) block. The contents will be unchanged up to the lesser of the new and old sizes. If the new size of the block requires movement of the block, the space for the previous instantiation of the block is freed. If the new size is larger, the contents of the newly allocated portion of the block are unspecified. If ptr is NULL, realloc() behaves like malloc() for the specified size. If size is 0 and ptr is not a null pointer, the space pointed to is freed. The malloc() and realloc() functions return a null pointer if there is not enough available memory. They return a non-null pointer if size is 0. These pointers should not be dereferenced. When realloc() returns NULL, the block pointed to by ptr is left intact. Always cast the value returned by malloc() and realloc(). If malloc() or realloc() returns unsuccessfully, errno will be set to indicate the following: ENOMEM size bytes of memory cannot be allocated because it exceeds the physical limits of the system. EAGAIN There is not enough memory available at this point in time to allocate size bytes of memory; but the application could try again later. Using realloc() with a block freed before the most recent call to malloc() or realloc() results in an error. Comparative features of the various allocation libraries can be found in the umem_alloc(3MALLOC) manual page. brk(2), malloc(3C), malloc(3MALLOC), mapmalloc(3MALLOC), umem_alloc(3MALLOC) WARNINGS
Use of libbsdmalloc renders an application non-SCD compliant. The libbsdmalloc routines are incompatible with the memory allocation routines in the standard C-library (libc): malloc(3C), alloca(3C), calloc(3C), free(3C), memalign(3C), realloc(3C), and valloc(3C). 21 Mar 2005 bsdmalloc(3MALLOC)
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