Very Computer

The whole thing is a bad juju, I suppose, but I'd like to know what would
happen. With the current implementation, at least.

Suppose I have a single-threaded program. At some point that program
dlopens a library which was compiled with -D_REENTRANT and is linked with
the thread library. In its normal course of operation the library wants to
create several threads which would perform whatever the library is
supposed to do. Would this work?

Is there any difference if the library is a direct dependency of the
executable?

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Linking issues aside, threaded executables run just fine on single-cpu
boxes. So unless there's some unstated requirement for
"These two threads must run simultaneously or the whole thing locks up"
you should be fine.

Mind you, there may well be such a requirement. If its your own code, you
can sort of cheat by doing a thr_setconcurrency() to 2 or more.
This cheats by timeslicing the threads.
Otherwise, the system defaults to (concurrency level)==(number of CPUs),
which has a tendancy to run the thread consecutively , rather than
concurrently.

[last I heard, which was back in solaris 2.6 or 7 anyways]

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The word of the day is mispergitude

This should not be a problem.

Quote:> Otherwise, the system defaults to (concurrency level)==(number of CPUs),
> which has a tendancy to run the thread consecutively , rather than
> concurrently.

I had something else in mind. With the normal MT program the thread library is
mapped and initialized before libc. In the above dlopen() scenario, libc would be
initialized and used before the thread library initialization. I don't know if
there are possible problems with this reversal. And when the program calls dlclose
(eventually), the library would be unmapped, but the thread library would stay for
the entire lifetime of the program.

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Nothing particularly bad happens.
The process just suddenly becomes multithreaded,
with all the implications thereof.

Quote:>Is there any difference if the library is a direct dependency of the
>executable?

Yes.  In this case, the process is multithreaded from the
outset, just as though it was linked directly with -lthread.

Roger Faulkner