Date: 01 Nov 1999 20:28:26 +0000 From: Randell Jesup <rjesup@wgate.com> To: freebsd-arch@freebsd.org Subject: Re: Threads goals version III Message-ID: <ybu1zaagdn9.fsf@jesup.eng.tvol.net.jesup.eng.tvol.net> In-Reply-To: Jake Burkholder's message of "Mon, 01 Nov 1999 15:17:42 -0800" References: <19991101231743.F30501FD7@io.yi.org>
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Jake Burkholder <jake@checker.org> writes:
>int global; /* all threads can access this */
>
>main() {
> thread t1;
> int mainvar;
>
> /* this could also be mmaped or stack based storage */
> t.stack = malloc(some memory);
What's this for? Wouldn't each new thread have it's own
stack space allocated by the thread library/kernel? (Perhaps
according to size requests in new_thread, or just an automatically
grown segment of the process (not thread) VM space.) Note: I haven't
looked at Unix thread library details.
> new_thread(&t1, foo, 1, &mainvar);
>foo(int ac, ...) {
> /* t1 now has access to mainvar through p */
>
>The WHOLE address space is shared. You can pass around
>pointers to stack based storage, but a new thread executes
>a new start_routine, so it can't access variables from the
>scope in which new_thread was called, only what get passed
>into start_routine.
Also, inter-thread IPC and implicit shared structures might
include pointers to stack variables, such as for a synchronous
request from another thread for data to be put into a buffer on the
stack, such as: (pseudo-code)
void
bar(unsigned char *encoded_data, unsigned long encoded_data_len)
{
unsigned char buffer[1000];
msg->out_buffer = &buffer[0];
msg->out_buflen = sizeof(buffer);
msg->in_buffer = encoded_data;
msg->in_buflen = encoded_data_len;
msg->command = DECODE_DATA;
// do_message is synchronous, sends a message and waits for a reply
do_message(decode_thread,msg);
// do something with buffer data
}
What synchronization (semaphores, etc) and inter-thread messaging
mechanisms are we thinking of?
--
Randell Jesup, Worldgate Communications, ex-Scala, ex-Amiga OS team ('88-94)
rjesup@wgate.com
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