NAME
psort, #ifdef UNIFDEF_BLOCKS psort_b, #endif psort_r – parallel sort functions
SYNOPSIS
#include <stdlib.h>
void
psort(void *base, size_t nel, size_t width, int *comparconst void *, const void *);
#ifdef UNIFDEF_BLOCKS
void
psort_b(void *base, size_t nel, size_t width, int ^comparconst void *, const void *);
#endif
void
psort_r(void *base, size_t nel, size_t width, void *thunk, int *comparvoid *, const void *, const void *);
DESCRIPTION
The #ifdef UNIFDEF_BLOCKS psort(), psort_b(), #else psort() #endif and psort_r() functions are parallel sort routines that are drop-in compatible with the corresponding qsort() function (see qsort(3) for a description of the arguments). On multiprocessor machines, multiple threads may be created to simultaneously perform the sort calculations, resulting in an overall faster sort result. Overhead in managing the threads limits the maximum speed improvement to somewhat less that the number of processors available. For example, on a 4-processor machine, a typical sort on a large array might result in 3.2 times faster sorting than a regular qsort().
RESTRICTIONS
Because of the multi-threaded nature of the sort, the comparison function is expected to perform its own synchronization that might be required for data physically outside the two objects passed to the comparison function. However, no synchronization is required for the two object themselves, unless some third party is also accessing those objects.
Additional memory is temporary allocated to deal with the parallel nature of the computation.
Because of the overhead of maintaining multiple threads, the psort() family of routines may choose to just call qsort(3) when there is no advantage to parallelizing (for example, when the number of objects in the array is too small, or only one processor is available).
Like qsort(3), the sort is not stable.
RETURN VALUES
The #ifdef UNIFDEF_BLOCKS psort(), psort_b() #else psort() #endif and psort_r() functions return no value.
SEE ALSO
SEE ALSO
sort(1), radixsort(3) Hoare, C.A.R., “Quicksort”, The Computer Journal, 5:1, pp. 10-15, 1962. Williams, J.W.J, “Heapsort”, Communications of the ACM, 7:1, pp. 347-348, 1964. Knuth, D.E., “Sorting and Searching”, The Art of Computer Programming, Vol. 3, pp. 114-123, 145-149, 1968. McIlroy, P.M., “Optimistic Sorting and Information Theoretic Complexity”, Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, January 1992. Bentley, J.L. and McIlroy, M.D., “Engineering a Sort Function”, Software--Practice and Experience, Vol. 23(11), pp. 1249-1265, November 1993.
STANDARDS
The qsort() function conforms to ISO/IEC 9899:1990 (“ISO C90”).