mutex_counter_ex

#!/bin/bash
#
# Example inspired by mutex-counter.go from the Go tutorial
# (https://go.dev/tour/concurrency/9).

readonly DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
. ${DIR}/../gobash


function SafeCounter() {
        # Including mutex as one of the fields.
        make_ $FUNCNAME \
              "mu" "$(Mutex)" \
              "v" "$(Map)"
}

function SafeCounter_inc() {
        local -r c="${1}"
        local -r key="${2}"
        shift 2

        # Lock mutex kept in this instance.
        $($c mu) lock

        $($c v) inc "${key}"

        # Unlock when the work is done.
        $($c mu) unlock
}

function SafeCounter_value() {
        local -r c="${1}"
        local -r key="${2}"
        shift 2

        $($c mu) lock
        local res=$($($c v) get "${key}")
        $($c mu) unlock

        echo "${res}"
}

function main() {
        local c
        c=$(SafeCounter) || assert_fail

        echo "Run increment in parallel with 10 subshells."
        for (( i=0; i<10; i++ )); do
                ( $c inc "somekey" ) &
        done
        echo "Wait for subshells to be done."
        wait || assert_fail

        $c value "somekey"
}

main

# Output will be:
# 10