ipcmutex: Inter-process locks and counters

In BiocParallel: Bioconductor facilities for parallel evaluation

Description

Functions documented on this page enable locks and counters between processes on the same computer.

Use ipcid() to generate a unique mutex or counter identifier. A mutex or counter with the same id, including those in different processes, share the same state.

ipcremove() removes external state associated with mutex or counters created with id.

ipclock() blocks until the lock is obtained. ipctrylock() tries to obtain the lock, returning immediately if it is not available. ipcunlock() releases the lock. ipclocked() queries the lock to determine whether it is currently held.

ipcyield() returns the current counter, and increments the value for subsequent calls. ipcvalue() returns the current counter without incrementing. ipcreset() sets the counter to n, such that the next call to ipcyield() or ipcvalue() returns n.

Usage

## Utilities

ipcid(id)

ipcremove(id)

## Locks

ipclock(id)

ipctrylock(id)

ipcunlock(id)

ipclocked(id)

## Counters

ipcyield(id)

ipcvalue(id)

ipcreset(id, n = 1)

Arguments

id	character(1) identifier string for mutex or counter. ipcid() ensures that the identifier is universally unique.
n	integer(1) value from which ipcyield() will increment.

Value

Locks:

ipclock() creates a named lock, returning TRUE on success.

trylock() returns TRUE if the lock is obtained, FALSE otherwise.

ipcunlock() returns TRUE on success, FALSE (e.g., because there is nothing to unlock) otherwise.

ipclocked() returns TRUE when id is locked, and FALSE otherwise.

Counters:

ipcyield() returns an integer(1) value representing the next number in sequence. The first value returned is 1.

ipcvalue() returns the value to be returned by the next call to ipcyield(), without incrementing the counter. If the counter is no longer available, ipcyield() returns NA.

ipcreset() returns n, invisibly.

Utilities:

ipcid() returns a character(1) unique identifier, with id (if not missing) prepended.

ipcremove() returns (invisibly) TRUE if external resources were released or FALSE if not (e.g., because the resources has already been released).

Examples

ipcid()

## Locks

id <- ipcid()

ipclock(id)
ipctrylock(id)
ipcunlock(id)
ipctrylock(id)
ipclocked(id)

ipcremove(id)

id <- ipcid()
system.time({
    ## about 1s, .2s for each process instead of .2s if no lock
    result <- bplapply(1:2, function(i, id) {
        BiocParallel::ipclock(id)
        Sys.sleep(.2)
        time <- Sys.time()
        BiocParallel::ipcunlock(id)
        time
    }, id)
})
ipcremove(id)
diff(sort(unlist(result, use.names=FALSE)))

## Counters

id <- ipcid()

ipcyield(id)
ipcyield(id)

ipcvalue(id)
ipcyield(id)

ipcreset(id, 10)
ipcvalue(id)
ipcyield(id)

ipcremove(id)

id <- ipcid()
result <- bplapply(1:2, function(i, id) {
    BiocParallel::ipcyield(id)
}, id)
ipcremove(id)
sort(unlist(result, use.names=FALSE))

BiocParallel documentation built on Nov. 8, 2020, 5:46 p.m.