From: Giacomo Tesio <giacomo@tesio.it>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
Subject: [9fans] Privalloc(2) and rfork(RFPROC|RFMEM) (was: a pair nec bugs)
Date: Sat, 5 Sep 2015 16:03:55 +0200 [thread overview]
Message-ID: <CAHL7psF6pK75inCaCd==Ay0eGmOm+QsqBjW2pM1F7HyTaWkNLg@mail.gmail.com> (raw)
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2011-05-20 3:30 GMT+02:00 erik quanstrom <quanstro@quanstro.net>:
> one note is that while i'm aware of privalloc(2), i didn't use it. the
> implementation doesn't appear correct for shared-memory procs.
> i think there are two issues
> - locking is unnecessary. the only preemptable unit of execution is
> a process and each process is guarenteed to have its own instance
> of _privates and _nprivates.
> - for shared-memory procs, we will run out of privates because
> the static privinit will be falsely shared. privinit should be replaced
> by using a private entry.
>
In a set of processes that share memory, I need a single per-process
location to store the address of structure (which is in turn allocated in
the global memory space).
Privalloc(2) seemed what I need, but seem that I can't use it properly.
In the parent process I do:
1) initialialize a global variable p = (MyStruct **)privalloc();
2) allocate a MyStruct for every process I'm going to spawn
3) spawn processes with rfork(RFMEM|RFPROC)
The spawn() function that call rfork takes a MyStruct* as argument and
assign it to *p in the new process.
For extra safety I added an assert(*p == nil) just after rfork, and after a
few (apparently?) successful spawns, the assert fails.
What I need is a sort of thread-local storage for the MyStruct*, so that
each child process can find it's own dedicated MyStruct.
I know that could get this with an hashtable based on the pid, but I'd
prefer to avoid the book keeping if possible.
Giacomo
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next reply other threads:[~2015-09-05 14:03 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-05 14:03 Giacomo Tesio [this message]
2015-09-05 14:11 ` Giacomo Tesio
2015-09-05 15:27 ` erik quanstrom
2015-09-05 16:41 ` erik quanstrom
2015-09-05 18:42 ` Giacomo Tesio
2015-09-05 18:47 ` erik quanstrom
2015-09-05 23:03 ` Giacomo Tesio
2015-09-05 18:56 ` cinap_lenrek
2015-09-05 22:45 ` Charles Forsyth
2015-09-05 23:38 ` cinap_lenrek
2015-09-06 13:14 ` erik quanstrom
2015-09-06 14:12 ` Charles Forsyth
2015-09-06 15:02 ` erik quanstrom
2015-09-06 20:21 ` Charles Forsyth
2015-09-07 0:30 ` erik quanstrom
2015-09-07 9:38 ` Charles Forsyth
2015-09-07 11:59 ` Charles Forsyth
2015-09-06 18:21 ` cinap_lenrek
2015-09-06 20:27 ` Charles Forsyth
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