Thread cap for matching

Matching runs on several threads with OpenMP when a call's subjects add up to more than an internal size threshold, and on one thread below it. re_threads() reports the most threads a call may use; re_threads(n) caps it for the rest of the session. The cap applies only to zuregex's own matching, not to other OpenMP code in the process.

Usage

re_threads(n = NULL)

Arguments

n

NULL to query the effective maximum, a whole number of at least 1 to cap the threads, or 0 to remove the cap. Values above the machine's thread count are allowed and are the same as no cap.

Value

Querying returns the effective maximum as an integer. Setting returns the previous cap invisibly, 0 meaning none was set, so old <- re_threads(1); re_threads(old) restores it exactly.

Details

Results never depend on the number of threads, so this is a performance control, not a reproducibility one. In a build without OpenMP the value is always 1 and a cap has no effect; zuregex_info() reports which build this is.

A forked child, such as a worker of parallel::mclapply(), matches on one thread, because GNU OpenMP can hang in a child whose parent has used it.

Examples

re_threads()
#> [1] 4
old <- re_threads(1)
re_threads(old)