Re: wait and ctrl+Z
On Fri, May 04, 2012 at 12:28:17AM +0200, Marc Glisse wrote: > On Fri, 4 May 2012, Herbert Xu wrote: > > Marc Glisse wrote: > >> Hello, > >> I noticed a strange behavior of "wait" when I suspend and resume a script. > >> $ cat a.sh > >> #!/bin/dash > >> (sleep 7; echo blah) & > >> (sleep 7; echo bloh) & > >> wait ; echo coucou > >> $ ./a.sh > >> ^Z > >> zsh: suspended ./a.sh > >> $ fg > >> [1] + continued ./a.sh > >> coucou > >> $ blah > >> bloh > >> As you can see, the instruction after "wait" was executed immediatly on > >> resume, without waiting for the jobs. > >> If I replace the ';' after "wait" by "&&" and do the same suspend+resume, > >> "coucou" is never printed. > >> I am using dash version 0.5.7-3 in debian testing. > > That's normal as wait was interrupted by a signal. If you want > > to wait even after an interruption, you should check the return > > value of wait. > Hello, and thanks for you answer. > I find that quite surprising. I re-read the posix description of wait, and > my understanding is that the return value of wait should depend on what > happened to the waited process (exit code, signal), not to wait itself. > And other shells seem to agree. This is not actually said in the XCU 'wait' page but in XCU 2.11 Signals and Error Handling. However, it says something subtly different: only a signal for which a trap has been set should cause 'wait' to return immediately with an exit status greater than 128. Because no trap has been set on SIGTSTP, 'wait' should not be interrupted here and the shell should continue waiting. Likewise, if the shell internally uses SIGCHLD to get notified about process termination, this does not interrupt 'wait'; dash implements that aspect properly. > Are you suggesting that wait should always be used in a loop? With what > check exactly? Only if you have set any traps that resume execution of the original script (i.e. do not exit the process). Otherwise, if 'wait' is being called without parameters, you can do something like until wait; do :; done If 'wait' is being called with parameters, the required loop is very complicated. -- Jilles Tjoelker -- To unsubscribe from this list: send the line "unsubscribe dash" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: wait and ctrl+Z
On Fri, 4 May 2012, Herbert Xu wrote: Marc Glisse wrote: Hello, I noticed a strange behavior of "wait" when I suspend and resume a script. $ cat a.sh #!/bin/dash (sleep 7; echo blah) & (sleep 7; echo bloh) & wait ; echo coucou $ ./a.sh ^Z zsh: suspended ./a.sh $ fg [1] + continued ./a.sh coucou $ blah bloh As you can see, the instruction after "wait" was executed immediatly on resume, without waiting for the jobs. If I replace the ';' after "wait" by "&&" and do the same suspend+resume, "coucou" is never printed. I am using dash version 0.5.7-3 in debian testing. That's normal as wait was interrupted by a signal. If you want to wait even after an interruption, you should check the return value of wait. Hello, and thanks for you answer. I find that quite surprising. I re-read the posix description of wait, and my understanding is that the return value of wait should depend on what happened to the waited process (exit code, signal), not to wait itself. And other shells seem to agree. Are you suggesting that wait should always be used in a loop? With what check exactly? -- Marc Glisse -- To unsubscribe from this list: send the line "unsubscribe dash" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: wait and ctrl+Z
Marc Glisse wrote: > Hello, > > I noticed a strange behavior of "wait" when I suspend and resume a script. > > $ cat a.sh > #!/bin/dash > (sleep 7; echo blah) & > (sleep 7; echo bloh) & > wait ; echo coucou > $ ./a.sh > ^Z > zsh: suspended ./a.sh > $ fg > [1] + continued ./a.sh > coucou > $ blah > bloh > > As you can see, the instruction after "wait" was executed immediatly on > resume, without waiting for the jobs. > > If I replace the ';' after "wait" by "&&" and do the same suspend+resume, > "coucou" is never printed. > > I am using dash version 0.5.7-3 in debian testing. That's normal as wait was interrupted by a signal. If you want to wait even after an interruption, you should check the return value of wait. Cheers, -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt -- To unsubscribe from this list: send the line "unsubscribe dash" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
wait and ctrl+Z
Hello, I noticed a strange behavior of "wait" when I suspend and resume a script. $ cat a.sh #!/bin/dash (sleep 7; echo blah) & (sleep 7; echo bloh) & wait ; echo coucou $ ./a.sh ^Z zsh: suspended ./a.sh $ fg [1] + continued ./a.sh coucou $ blah bloh As you can see, the instruction after "wait" was executed immediatly on resume, without waiting for the jobs. If I replace the ';' after "wait" by "&&" and do the same suspend+resume, "coucou" is never printed. I am using dash version 0.5.7-3 in debian testing. -- Marc Glisse -- To unsubscribe from this list: send the line "unsubscribe dash" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
