Wait until a process comes back from sleep

If you know N beforehand, you can use fifo as a semaphore.

mkfifo sem; exec 3<>sem rm -f sem 

Then make each N>1 process read a byte from that &3. Since those bytes won't initially be available, it'll put them to sleep as well.

Once N==1 is done sleeping, it can write a N bytes into &3, waking up each process that has been waiting on a byte from &3.

#!/bin/bash -e mkfifo p exec 3<>p rm p main()( echo $FUNCNAME beg sleep 2 &>/dev/null printf '\n\n\n' >&3 echo $FUNCNAME end ) worker()( echo $FUNCNAME$1 beg read -n 1 <&3 echo $FUNCNAME$1 end ) main & worker 1 & worker 2 & worker 3 & wait 

Output:

main beg worker1 beg worker2 beg worker3 beg main end worker2 end worker3 end worker1 end 

Another way to do this might be with signals. If you can make sure your script is run as a terminal job with $$ (parent shell pid) being the process group id of the corresponding process group, then you can make your workers sleep indefinitely (ideally with processes calling the pause function; or with sleep $hugevalue if you can't do the former) and before that, make them establish a handler e.g., for SIGUSR1. The main process first worker should ignore the signal. The first worker can then singnal all other workers by kill -SIGUSR1 -$$, which will kill the indefinite sleepers, making the workers continue.

#!/bin/bash trap ' ' SIGUSR1 main()( trap - SIGUSR1 echo $FUNCNAME beg sleep 2 &>/dev/null echo $FUNCNAME end kill -s SIGUSR1 -$$ ) worker()( trap ' ' SIGUSR1 echo $FUNCNAME$1 beg sleep 10000000000 &>/dev/null echo $FUNCNAME$1 end ) main & worker 1 & worker 2 & worker 3 & wait 

Output:

main beg worker2 beg worker1 beg worker3 beg main end User defined signal 1 worker1 end User defined signal 1 worker3 end User defined signal 1 [1] 31554 user-defined signal 1 ./scr1 

(I don't know how to turn off the "user-defined signal 1" messages)

Without seeing a snippet of your code I can only guess that it might be something like this:

for k in $(seq $N) do script.sh & done 

So, in order to wait for the first one to complete before firing off the others you could do something like this:

for k in $(seq $N) do script.sh & [[ $k == 1 ]] && wait done 

If the script itself takes a significant period of time to run this won't resolve your requirement as written, but unless you can separate the sleep from the processing I don't believe it's going to be sanely possible to achieve your requirement and still satisfy your stated criteria.