Condition Variables — cv • nanonext

cv creates a new condition variable (protected by a mutex internal to the object).

wait waits on a condition being signalled by completion of an asynchronous receive or pipe event.
wait_ is a variant that allows user interrupts, suitable for interactive use.

until waits until a future time on a condition being signalled by completion of an asynchronous receive or pipe event.
until_ is a variant that allows user interrupts, suitable for interactive use.

cv_value inspects the internal value of a condition variable.

cv_reset resets the internal value and flag of a condition variable.

cv_signal signals a condition variable.

Usage

cv()

wait(cv)

wait_(cv)

until(cv, msec)

until_(cv, msec)

cv_value(cv)

cv_reset(cv)

cv_signal(cv)

Arguments

cv: a ‘conditionVariable’ object.
msec: maximum time in milliseconds to wait for the condition variable to be signalled.

Value

For cv: a ‘conditionVariable’ object.

For wait: (invisibly) logical TRUE, or else FALSE if a flag has been set.

For until: (invisibly) logical TRUE if signalled, or else FALSE if the timeout was reached.

For cv_value: integer value of the condition variable.

For cv_reset and cv_signal: zero (invisibly).

Details

Pass the ‘conditionVariable’ to the asynchronous receive functions recv_aio or request. Alternatively, to be notified of a pipe event, pass it to pipe_notify.

Completion of the receive or pipe event, which happens asynchronously and independently of the main R thread, will signal the condition variable by incrementing it by 1.

This will cause the R execution thread waiting on the condition variable using wait or until to wake and continue.

For argument ‘msec’, non-integer values will be coerced to integer. Non-numeric input will be ignored and return immediately.

Condition

The condition internal to this ‘conditionVariable’ maintains a state (value). Each signal increments the value by 1. Each time wait or until returns (apart from due to timeout), the value is decremented by 1.

The internal condition may be inspected at any time using cv_value and reset using cv_reset. This affords a high degree of flexibility in designing complex concurrent applications.

Flag

The condition variable also contains a flag that certain signalling functions such as pipe_notify can set. When this flag has been set, all subsequent wait calls will return logical FALSE instead of TRUE.

Note that the flag is not automatically reset, but may be reset manually using cv_reset.

Examples

cv <- cv()

if (FALSE) { # \dontrun{
wait(cv) # would block until the cv is signalled
wait_(cv) # would block until the cv is signalled or interrupted
} # }

until(cv, 10L)
until_(cv, 10L)

cv_value(cv)
#> [1] 0

cv_reset(cv)

cv_value(cv)
#> [1] 0
cv_signal(cv)
cv_value(cv)
#> [1] 1