wait for several system calls to finish

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SA-W 2024-4-20

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评论： Mario Malic 2024-4-27

I am calling three external programs and can only continue in the matlab program after all programs are finished. Each of them work independently of each other and can start at the same time

[staus1,~] = system('cmd1 &');
[staus2,~] = system('cmd2 &');
[staus3,~] = system('cmd3 &');
% how to check if all of them are finished?

Using ampersand & symbol, I reached that they start nearly at the same time, but how can I check when they are all finished? In my case, the returned status variables can be zero (successful) or negative (not successful). Hence, checking status for any value does not help, I guess.

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Walter Roberson 2024-4-20

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You have to use taskmgr (Windows) or ps (MacOS or Linux) to detect whether the processes are still alive.

Note: If you are using Windows then I recommend that you instead use System.Diagnostics.Process which is able to start processes independently, and allows their status to be checked.

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Walter Roberson 2024-4-21

在 MATLAB Online 中打开

You could use

ps | grep matlab | tail

and parse out the process ID. Then you could start the new process, and then

ps -g PROCESS_ID_GOES_HERE

to get the process ID of the new process.

Then you could use the java watcher https://www.mathworks.com/matlabcentral/answers/398152-listening-to-the-creation-deletion-of-a-file-with-specific-name#answer_317920 on /proc/PROCESS_ID_OF_NEW_PROCESS watching for deletion

... something like that

SA-W 2024-4-25

@Walter Roberson As for this solution: I found a way to extract the process id's of interest. Also, watchting /proc/PROCESS_ID for deletion is doable. However, it is not clear to me how I can extract the exit status of my program. When I do

[status,~] = system('myprog')

When I start the system commands in background (appending &), we have status=0, but this is not the real exit status of my program which is the integer returned in the main function of myprog.

Any idea how I can get this?

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Mario Malic 2024-4-20

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Ampersand means that program will be started and MATLAB will not wait for it to be terminated and will continue to execute next lines of code.

What does it mean that they are finished? Does the program exits when it's done?

You can remove ampersand, then you have to close the program for MATLAB to execute next lines.

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Walter Roberson 2024-4-26

I cannot think of any way to get the information about the process exit status.

Mario Malic 2024-4-27

If I understood correctly, multistart does that already, it has multiple starting points. By running multistart in parallel, each of these runs may lead to the minimum that already has been found by some other multistart process.

If you are looking for a any (tedious) solution, you could write a file from your c++ code indicating the exit status and read it with MATLAB once process is deleted.

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