On Monday, April 24, 2000, Brian O'Shea wrote:
> On Mon, Apr 24, 2000 at 06:13:53AM -0400, Daniel Eischen wrote:
> > On Mon, 24 Apr 2000, Brian O'Shea wrote:
> > >
> > > I was under the impression that, because user thread scheduling is done
> > > in user mode, a thread that goes to sleep calling a blocking read()
> > > system call will put the entire process to sleep until that read()
> > > returns (and so all user threads in the process will also be blocked).
> > > Is this correct?
> >
> > 1. You are mistaken.
>
> Could you elaborate? The text that I am using [1] warns about blocking
> system calls putting the process (and thus all user threads) to sleep.
> This book has no FreeBSD specific information, so anything specific to
> FreeBSD would be really interesting to hear.
FreeBSD's threads implement has its own read() function which
will make a non-blocking read() call (using the _real_ syscall)
for the specified amount of bytes. Now a non-blocking read()
call fails unless all the data in nbytes can be read into buf.
So our implementation will continue to do a non-blocking read
until all the data can be copied and then allows the thread
continue, thus blocking only the calling thread.
At least that's what the source code tells me.
--
|Chris Costello <[EMAIL PROTECTED]>
|I smell a wumpus.
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