On Tue, Nov 14, 2000 at 12:35:55AM -0500, Dingrong Yi wrote:
# Hello everyone,
#
# I have some questions concerning the communications between user space
# program and the rtlinux program by fifo.
#
# Consider such a scenerio, one rtlinux's program and one normal linux
# program. The rtlinux program write to a fifo with
# very high rate a structure, and the fifo is created to be the same size
# as that of the structure. The user program read the same structure from
# that same fifo.
#
# What will happen that during the user program is reading from
# the fifo when rtlinux program come and take the resource over ? I can not
# imagine how this issue be dealt with rtlinux.
i guess, this is not going to happen. because linux(and all processes run within it)
and realtime tasks are scheduled so that when one runs the other is suspended. linux
itself is a lowest priority thread, and as long as there will be any realtime task
executing, linux won't run (won't get any cpu time share). saying `linux' i mean linux
kernel processes and userspace processes as a whole.
# Another issue, consider again a rtlinux process, and a normal process.
# This time the normal process write a structure to a fifo and the rtlinux
# read it. What will happen that when the linux process only write half of
# the fifo when the rtlinux come to read it?
the rtlinux task will read all the data available with no exception. rtf_get()
function returns number of actually read bytes, which could be less than
sizeof(your_structure).
btw, the same with writing to fifo: if your linux process writes data at high rate and
the fifo size is the size of structure, the following could happen: if your linux
process won't readthe fifo fast, the rtlinux process may not be able to write to the
fifo at some point, because it will be full.
# Are such issues are considered already by rtlinux kernel or the user (like
# me) of rtlinux should take care of it ?
i think that abovementioned issues are handled by kernel.
rgds,
Denis.
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