On 2/8/19 12:39 PM, Eric Blake wrote: > On 2/8/19 11:26 AM, Peng Yu wrote: > >>> Come on. If you're not going to read the code, at least read the comments. >> >> This is what I don't understand. Why caching pointers not caching the >> actual memory allocated to the string can improve the performance? >> >>> /* Create an object cache C of N pointers to OTYPE. */ >>> >>> /* Free all cached items, which are pointers to OTYPE, in object cache C. */ > > A cache of pointers means that the next time you need a fresh pointer to > the same object type, you can reuse the allocated memory still pointed > to by an older pointer already found in the cache (fast) rather than > having to call malloc() (slow). Since all of the pointers are pointing > to memory of the same size (namely, sizeof(OTYPE)), you don't have to > worry about whether your reuse of the area is going to overwrite more > memory than the previous use of that area. > > Apparently, you are confused on the data type being cached - it is NOT a > cache of the user-supplied strings, but of the WORD_DESC and WORD_LIST > structures used to manage groups of user-supplied strings. While we > have to eat the cost of malloc()ing user-supplied strings of unknown > lengths, the cache at least lets us avoid even more malloc()s of the > fixed-size management data structures.
I would add that WORD_DESCs and WORD_LISTs are by far the most-used shell
data objects.
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU c...@case.edu http://tiswww.cwru.edu/~chet/
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