Thanks for the explanation, and sorry for being dense in my initial reading of it. Memsetting one gig of RAM takes 1.4 seconds for me. Imagine the amount of actual work that computer could've done in that time instead. Congratulations on your fast computer though.
Yeah man, honestly I don't know what he's talking about with his benchmark. I just ran my own really quick test comapring a calloc'ing vs the malloc -> memset sequence and they are darn near identical. Which makes sense because calloc has to bring in pages and once you touch the malloc'd page it has to be pulled in too. Worse, my laptop only has a gig of ram, so deity forbid I attempt to calloc or malloc and memset a gig, I'll start swapping! But, unsurprisingly, I can call malloc for a gig of ram and it'll return immediately. So long as I don't touch the pages, it'll never slow down.
Point is, calloc is different than malloc and shouldn't be used unless you need all your memory zero'd. And really, what application does? Most malloc's would be followed by something "useful" like a memcpy or filling in the malloc'd memory with useful data. Further, you most certainly wouldn't use calloc for a sparse array, that'd just be crazy.
P.S. here's uname -a
edit: I just ran it on a work machine, memcpy followed by memset for 1 GB and calloc for 1 GB were also identical and about 2 seconds. This is on an P570 frame with 12 GB of memory and a 2 CPU's allocated. So...I'd love to know what computer does it in "fractions of a second".
edit2: I suppose I also stirred this up, by saying "I'll wait" as if to imply it'd be ages. But, in computer terms, 2 seconds is "ages". Plus, if you had to swap, it'd really be "I'll wait" because on my poor laptop with 1 GB of RAM, asking it to memset (or calloc) a gig started it swapping; my music in the background was starting to skip and the harddrive started to spin as memory was being paged to disc. It was BAD, lol. After I killed the process, it still took about 10 seconds for the poor thing to normalize, and my music player hung and wouldn't come back, so I had to kill it, lol. Fortunately, the same program without the memset (and just the malloc) ran and ended immediately, because it just pulled in address space to the process, never a physical page, and so never did any actual work. Hence the BIG difference between malloc and calloc that started this whole off topic thread of communication.
Last edited by DreamWarrior; 10-20-2011 at 09:26 PM..
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