I had trouble with @PSkocik's solution. My system does not have GNU Parallel available as a package and sem threw an exception when I built and ran it manually. I then tried the FIFO semaphore example as well which also threw some other errors regarding communication.

@eyeApps suggested xargs but I didn't know how to make it work with my complex use case (examples would be welcome).

Here is my solution for parallel jobs which process up to N jobs at a time as configured by _jobs_set_max_parallel:

_lib_jobs.sh:

function _jobs_get_count_e {
   jobs -r | wc -l | tr -d " "
}

function _jobs_set_max_parallel {
   g_jobs_max_jobs=$1
}

function _jobs_get_max_parallel_e {
   [[ $g_jobs_max_jobs ]] && {
      echo $g_jobs_max_jobs
      
      return 0
   }
   
   echo 1
}

function _jobs_is_parallel_available_r() {
   (( $(_jobs_get_count_e) < $g_jobs_max_jobs )) &&
      return 0
   
   return 1
}

function _jobs_wait_parallel() {
   # Sleep between available jobs
   while true; do
      _jobs_is_parallel_available_r &&
         break
      
      sleep 0.1s
   done
}

function _jobs_wait() {
   wait
}

Example usage:

#!/bin/bash

source "_lib_jobs.sh"

_jobs_set_max_parallel 3

# Run 10 jobs in parallel with varying amounts of work
for a in {1..10}; do
   _jobs_wait_parallel
   
   # Sleep between 1-2 seconds to simulate busy work
   sleep_delay=$(echo "scale=1; $(shuf -i 10-20 -n 1)/10" | bc -l)
   
   ( ### ASYNC
   echo $a
   sleep ${sleep_delay}s
   ) &
done

# Visualize jobs
while true; do
   n_jobs=$(_jobs_get_count_e)
   
   [[ $n_jobs = 0 ]] &&
      break
   
   sleep 0.1s
done

I had trouble with @PSkocik's solution. My system does not have GNU Parallel available as a package and sem threw an exception when I built and ran it manually. I then tried the FIFO semaphore example as well which also threw some other errors regarding communication.

@eyeApps suggested xargs but I didn't know how to make it work with my complex use case (examples would be welcome).

Here is my solution for parallel jobs which process up to N jobs at a time as configured by _jobs_set_max_parallel:

_lib_jobs.sh:

function _jobs_get_count_e {
   jobs -r | wc -l | tr -d " "
}

function _jobs_set_max_parallel {
   g_jobs_max_jobs=$1
}

function _jobs_get_max_parallel_e {
   [[ $g_jobs_max_jobs ]] && {
      echo $g_jobs_max_jobs
      
      echo 0
   }
   
   echo 1
}

function _jobs_is_parallel_available_r() {
   (( $(_jobs_get_count_e) < $g_jobs_max_jobs )) &&
      return 0
   
   return 1
}

function _jobs_wait_parallel() {
   # Sleep between available jobs
   while true; do
      _jobs_is_parallel_available_r &&
         break
      
      sleep 0.1s
   done
}

function _jobs_wait() {
   wait
}

Example usage:

#!/bin/bash

source "_lib_jobs.sh"

_jobs_set_max_parallel 3

# Run 10 jobs in parallel with varying amounts of work
for a in {1..10}; do
   _jobs_wait_parallel
   
   # Sleep between 1-2 seconds to simulate busy work
   sleep_delay=$(echo "scale=1; $(shuf -i 10-20 -n 1)/10" | bc -l)
   
   ( ### ASYNC
   echo $a
   sleep ${sleep_delay}s
   ) &
done

# Visualize jobs
while true; do
   n_jobs=$(_jobs_get_count_e)
   
   [[ $n_jobs = 0 ]] &&
      break
   
   sleep 0.1s
done

I had trouble with @PSkocik's solution. My system does not have GNU Parallel available as a package and sem threw an exception when I built and ran it manually. I then tried the FIFO semaphore example as well which also threw some other errors regarding communication.

@eyeApps suggested xargs but I didn't know how to make it work with my complex use case (examples would be welcome).

Here is my solution for parallel jobs which process up to N jobs at a time as configured by _jobs_set_max_parallel:

function _jobs_get_count_e {
   jobs -r | wc -l | tr -d " "
}

function _jobs_set_max_parallel {
   g_jobs_max_jobs=$1
}

function _jobs_get_max_parallel_e {
   [[ $g_jobs_max_jobs ]] && {
      echo $g_jobs_max_jobs
      
      return 0
   }
   
   echo 1
}

function _jobs_is_parallel_available_r() {
   (( $(_jobs_get_count_e) < $g_jobs_max_jobs )) &&
      return 0
   
   return 1
}

_jobs_set_max_parallel 3

for a in {1..10}; do
   # Sleep between available jobs
   while true; do
      _jobs_is_parallel_available_r &&
         break
      
      sleep 0.1s
   done
   
   # Sleep between 1-2 seconds to simulate busy work
   sleep_delay=$(echo "scale=1; $(shuf -i 10-20 -n 1)/10" | bc -l)
   
   ( ### ASYNC
   echo $a
   sleep ${sleep_delay}s
   ) &
done

# Visualize jobs
while true; do
   n_jobs=$(_jobs_get_count_e)
   
   [[ $n_jobs = 0 ]] &&
      break
   
   sleep 0.1s
done

I had trouble with @PSkocik's solution. My system does not have GNU Parallel available as a package and sem threw an exception when I built and ran it manually. I then tried the FIFO semaphore example as well which also threw some other errors regarding communication.

@eyeApps suggested xargs but I didn't know how to make it work with my complex use case (examples would be welcome).

Here is my solution for parallel jobs which process up to N jobs at a time as configured by _jobs_set_max_parallel:

_lib_jobs.sh:

function _jobs_get_count_e {
   jobs -r | wc -l | tr -d " "
}

function _jobs_set_max_parallel {
   g_jobs_max_jobs=$1
}

function _jobs_get_max_parallel_e {
   [[ $g_jobs_max_jobs ]] && {
      echo $g_jobs_max_jobs
      
      return 0
   }
   
   echo 1
}

function _jobs_is_parallel_available_r() {
   (( $(_jobs_get_count_e) < $g_jobs_max_jobs )) &&
      return 0
   
   return 1
}

function _jobs_wait_parallel() {
   # Sleep between available jobs
   while true; do
      _jobs_is_parallel_available_r &&
         break
      
      sleep 0.1s
   done
}

function _jobs_wait() {
   wait
}

Example usage:

#!/bin/bash

source "_lib_jobs.sh"

_jobs_set_max_parallel 3

# Run 10 jobs in parallel with varying amounts of work
for a in {1..10}; do
   _jobs_wait_parallel
   
   # Sleep between 1-2 seconds to simulate busy work
   sleep_delay=$(echo "scale=1; $(shuf -i 10-20 -n 1)/10" | bc -l)
   
   ( ### ASYNC
   echo $a
   sleep ${sleep_delay}s
   ) &
done

# Visualize jobs
while true; do
   n_jobs=$(_jobs_get_count_e)
   
   [[ $n_jobs = 0 ]] &&
      break
   
   sleep 0.1s
done