On Mon, Feb 24 2020 10:24:53 +0100, Martin Pieuchot wrote: > On 23/02/20(Sun) 14:48, Lauri Tirkkonen wrote: > > I was working on a make jobserver implementation that uses POSIX > > semaphores as job tokens instead of a complicated socket-based approach. > > Initially I used named semaphores, which work fine, except if child > > processes with less privileges need to also open the named semaphore > > (eg. 'make build' as root executing 'su build -c make'). For that reason > > I wanted to use an unnamed semaphore (sem_init()) which is stored in shm > > -- that way I could leave the shm fd open and pass it to children. > > > > But unfortunately, sem_t is currently just a pointer to the opaque > > struct __sem, and sem_int() always calloc()s the storage for the struct. > > That's by design.
Ok - could you elaborate what the design is? > > This means the application cannot control where unnamed semaphores are > > stored, so I can't put it in shm. > > Are you trying to use semaphore shared between process? Did you called > sem_init() with pshared=1? Have you seen that the current implementation > doesn't support them? Yes, that's what I'm trying to do. Yes, I've seen the current implementation -- that's why I started this thread, in an attempt to make them supported. :) See the followup patch -- sharing the semaphore between processes does work with it. -- Lauri Tirkkonen | lotheac @ IRCnet
