识别shell中触发的并行进程的结束时间戳

Question

process p3 completes first than the other two but the process is waiting till the process p1 is completed and the end_time is the same for all the 3 processes. But i want to get the timestamp of p3 process as soon as it is completed and the same with p2 and p1. Thanks in advance

p1_start_time=`date "+%Y-%m-%d %H:%M:%S"`
sleep 100 &
p1=$!

p2_start_time=`date "+%Y-%m-%d %H:%M:%S"`
sleep 60 &
p2=$!

p3_start_time=`date "+%Y-%m-%d %H:%M:%S"`
sleep 20 &
p3=$!


$(wait $p1 ; rc=$? ; p1_end_time=`date "+%Y-%m-%d %H:%M:%S"`) &
$(wait $p2 ; rc=$? ; p2_end_time=`date "+%Y-%m-%d %H:%M:%S"`) &
$(wait $p3 ; rc=$? ; p3_end_time=`date "+%Y-%m-%d %H:%M:%S"`) &

wait

echo "out of wait"

echo "$p1_end_time"
echo "$p2_end_time"
echo "$p3_end_time"

Answer 1

The 3x backgrounded (aka 'child') pids (p1 / p2 / p3) are available to the main/calling process (aka the 'parent'). Only the 'parent' process can use the wait command to wait for the 'child' processes to complete.

For each of the $(wait $p ...) constructs a separate OS-level process is spawned and while you can pass the background pids to these new processes, said processes are not the 'parent' of said background pids; the net effect is the three wait $p# calls are (effectively) ignored and the 3x p#_end_time variables are immediately populated with the current date/time. But, keep in mind the 3x p#_end_time variables are being assigned within separate sub-processes which means when said processes exit the associated p#_end_time variables are discarded (ie, the values are not passed back 'up' to the main/calling process).

Also keep in mind that when a process is put in the background it is executed asynchronously, which means a separate OS-level process is spawned. In order to pass data back 'up' to the main/calling process (eg, in this case the end time of the background processes) it becomes necessary to implement some sort of inter-process communications or use an intermediate storage option for sharing data (eg, pipe, file, database table, queuing system, etc).

One idea for capturing the separate end times:

• upon exiting the sleep , write the current date/time to a temp file; this is how we'll pass data 'up' from the background (aka child) processes to the parent process
• while not an issue for this scenario, we'll have each child process write to a separate temp file to alleviate any issues with race conditions and scrambling of data when multiple processes write to the same file at the same time
• for this answer I'm going to use a couple arrays to store the start and end times; this allows for a little less coding by using a couple loops
• if the OP needs to use explicit variables for each start/end pair then the loops can be replaced with individual calls using the explicit variable names

One implementation:

unset pstart pend                                 # delete any variables with these names
pstart=()                                         # init arrays for
pend=()                                           # start and end times

outdir=$(mktemp -d)                               # create temp directory for storing temp files containing end date/times

stime=100                                         # initial sleep time

for i in {1..3}                                   # we'll do 3x passes through the loop
do
    pstart["${i}"]=$(date "+%Y-%m-%d %H:%M:%S")   # save the start date/time

    # kick off sleep + 'echo date/time > temp file' in the background; each sub-process will have a different OS-level pid == BASHPID

    (sleep "${stime}"; echo "${i} "$(date "+%Y-%m-%d %H:%M:%S") > "${outdir}/${BASHPID}") &

    stime=$((stime-40))                           # OP's example just happens to use times that are 40 seconds apart
done

wait                                              # wait for all background processes to complete

# load our end times into the pend array

while read -r i dt
do
    pend["${i}"]="${dt}"
done < <(cat "${outdir}"/[0-9]*)

# display start/end times for our processes (OP can reformat as needed)

for i in {1..3}
do
    echo "process #${i} start/end times: ${pstart[${i}]} - ${pend[${i}]}"
done

# get rid of the temp directory and files

'rm' -rf "${outdir}" >/dev/null 2>&1

The output from a sample run:

process #1 start/end times: 2020-10-14 22:49:28 - 2020-10-14 22:51:08
process #2 start/end times: 2020-10-14 22:49:28 - 2020-10-14 22:50:28
process #3 start/end times: 2020-10-14 22:49:28 - 2020-10-14 22:49:48