If you want to try it yourself and report back, I'm sure we'd all be interested in what you find out. The main thing I'm aware of is that copy-on-write works very well for preforking and threads usually can't match it, but maybe your application is different.
Regarding your thread-safety questions, chdir() is global to the process, so not thread-safe. I think the issue with readdir() is that open directory handles don't get copied when threads are spawned, but maybe there's more to it. The special Perl vars are not a problem with threads, since each thread is a separate interpreter. You can read about the limitations of threads here: http://perldoc.perl.org/threads.html#BUGS-AND-LIMITATIONS - Perrin On Mon, Apr 4, 2016 at 5:03 PM, Ben RUBSON <ben.rub...@gmail.com> wrote: > Hi Perrin, > > Thank you for your answer. > > Well, for the moment I only use the prefork (non-threaded) MPM. > But I would have liked to test performance of the threaded MPM, so I would > have liked my code to be thread-ready. > > According to this : > > https://perl.apache.org/docs/2.0/user/performance/mpm.html#toc_Memory_Requirements_in_Threaded_MPM > Sounds like threads could have an interest, but according to your message, > should not be a general case. > > Thank you, > > Ben > > Le 4 avr. 2016 à 22:49, Perrin Harkins <phark...@gmail.com> a écrit : > > Hi Ben. > > Before you get too far into the details of using threads, can I ask why > you're considering it? The memory footprint and performance of using forked > processes with Perl is generally going to be better than that of threads, > due to copy-on-write. > > - Perrin > > On Mon, Apr 4, 2016 at 4:44 PM, Ben RUBSON <ben.rub...@gmail.com> wrote: > >> Hello, >> >> I have some questions regarding mod_perl, threads, thread-safe functions, >> special vars scope... >> >> From >> https://perl.apache.org/docs/2.0/user/coding/coding.html#toc_Thread_environment_Issues >> : >> "if you chdir() in one thread, all other thread now see the current >> working directory of that thread that chdir()'ed to that directory" >> Do we speak about threads from threaded MPM ? >> (so the specific Apache process which owns the thread running this Perl >> script, and all its (the process) threads, will chdir()). >> >> From the same page : >> "Other usually problematic (non thread-safe) functions include readdir(), >> srand(), etc." >> Why readdir() would not be thread-safe ? I can't see why. Perhaps >> readdir() chdir() to read a directory content ? >> How could we then read dir content being thread-safe ? >> >> From >> https://perl.apache.org/docs/general/perl_reference/perl_reference.html#toc_The_Scope_of_the_Special_Perl_Variables >> : >> "In the mod_perl situation where the child server doesn't usually exit, >> if in one of your scripts you modify a global variable it will be changed >> for the rest of the process' life and will affect all the scripts executed >> by the same process." >> So in a threaded MPM, if one of the threads modifies one of the special >> Perl variables, it will instantly affect all other threads of this process ? >> >> What about variables like $? ? (return code of system() calls) >> And ${^CHILD_ERROR_NATIVE} ? (return code too) >> Does their value stay local to the thread ? / Does each thread have these >> variables with their own proper value ? >> Or is it unsafe to read them because they could be modified by another >> thread ? >> >> Thank you very much for your clarification, >> >> Best regards, >> >> Ben >> >> > >
