minix/lib/libsys/asynsend.c
Thomas Veerman 2cde22ee10 Enable a process to find out what the error code was when delivery of an
asynchronous message resulted in an error.

The model here is that:
 - Iff a sender wishes to be notified, the sender MUST check for errors
   BEFORE sending another asynchronous message.

The reason is that in order to remember the error code, we can't clean up
the message table and hence we risk running out of table space. This is
less of a problem when the sender enables notifications only for errors.
2011-04-08 15:23:12 +00:00

179 lines
4.7 KiB
C

#define _MINIX 1
#define _SYSTEM 1
#include <minix/config.h>
#include <minix/ansi.h>
#include <assert.h>
#include <sys/types.h>
#include <minix/const.h>
#include <minix/type.h>
#include <stdlib.h>
#include <unistd.h>
#include <minix/syslib.h>
#include <minix/sysutil.h>
#include <minix/sys_config.h>
#include <limits.h>
#include <errno.h>
#define ASYN_NR (2*_NR_PROCS)
PRIVATE asynmsg_t msgtable[ASYN_NR];
PRIVATE int first_slot = 0, next_slot = 0;
PRIVATE int initialized = 0;
/*===========================================================================*
* asynsend3 *
*===========================================================================*/
PUBLIC int asynsend3(dst, mp, fl)
endpoint_t dst;
message *mp;
int fl;
{
int i, r, src_ind, dst_ind;
unsigned flags;
static int inside = 0;
int len, needack = 0;
/* Debug printf() causes asynchronous sends? */
if (inside) /* Panic will not work either then, so exit */
exit(1);
inside = 1;
if(!initialized) {
/* Initialize table by marking all entries empty */
for (i = 0; i < ASYN_NR; i++) msgtable[i].flags = AMF_EMPTY;
initialized = 1;
}
/* Update first_slot. That is, find the first not-completed slot by the
* kernel since the last time we sent this table (e.g., the receiving end of
* the message wasn't ready yet).
*/
for (; first_slot < next_slot; first_slot++) {
flags = msgtable[first_slot].flags;
if ((flags & (AMF_VALID|AMF_DONE)) == (AMF_VALID|AMF_DONE)) {
/* Marked in use by us (VALID) and processed by the kernel */
if (msgtable[first_slot].result != OK) {
#if NDEBUG
printf("asynsend: found entry %d with error %d\n",
first_slot, msgtable[first_slot].result);
#endif
needack = (flags & (AMF_NOTIFY|AMF_NOTIFY_ERR));
}
continue;
}
if (flags != AMF_EMPTY)
/* Found first not-completed table entry */
break;
}
/* Reset to the beginning of the table when all messages are completed */
if (first_slot >= next_slot && !needack)
next_slot = first_slot = 0;
/* Can the table handle one more message? */
if (next_slot >= ASYN_NR) {
/* We're full; tell the kernel to stop processing for now */
if ((r = senda(NULL, 0)) != OK)
panic("asynsend: senda failed: %d", r);
/* Move all unprocessed messages to the beginning */
dst_ind = 0;
for (src_ind = first_slot; src_ind < next_slot; src_ind++) {
flags = msgtable[src_ind].flags;
/* Skip empty entries */
if (flags == AMF_EMPTY) continue;
/* and completed entries only if result is OK or if error
* doesn't need to be acknowledged */
if ((flags & (AMF_VALID|AMF_DONE)) == (AMF_VALID|AMF_DONE)) {
if (msgtable[src_ind].result == OK)
continue;
else {
#if NDEBUG
printf(
"asynsend: found entry %d with error %d\n",
src_ind, msgtable[src_ind].result);
#endif
if (!(flags & (AMF_NOTIFY|AMF_NOTIFY_ERR)))
/* Don't need to ack this error */
continue;
}
}
/* Copy/move in use entry */
#if NDEBUG
printf("asynsend: copying entry %d to %d\n", src_ind, dst_ind);
#endif
if (src_ind != dst_ind) msgtable[dst_ind] = msgtable[src_ind];
dst_ind++;
}
/* Mark unused entries empty */
for (i = dst_ind; i < ASYN_NR; i++) msgtable[i].flags = AMF_EMPTY;
first_slot = 0;
next_slot = dst_ind;
if (next_slot >= ASYN_NR) /* Cleanup failed */
panic("asynsend: msgtable full");
}
fl |= AMF_VALID; /* Mark in use */
msgtable[next_slot].dst = dst;
msgtable[next_slot].msg = *mp;
msgtable[next_slot].flags = fl; /* Has to be last. The kernel
* scans this table while we
* are sleeping.
*/
next_slot++;
assert(next_slot >= first_slot);
len = next_slot - first_slot;
assert(first_slot + len <= ASYN_NR);
assert(len >= 0);
inside = 0;
/* Tell the kernel to rescan the table */
return senda(&msgtable[first_slot], len);
}
/*===========================================================================*
* asyn_geterror *
*===========================================================================*/
PUBLIC int asyn_geterror(endpoint_t *dst, message *msg, int *err)
{
int src_ind, flags, result;
if (!initialized) return(0);
for (src_ind = 0; src_ind < next_slot; src_ind++) {
flags = msgtable[src_ind].flags;
result = msgtable[src_ind].result;
/* Find a message that has been completed with an error */
if ((flags & (AMF_VALID|AMF_DONE)) == (AMF_VALID|AMF_DONE)) {
if (result != OK && (flags & (AMF_NOTIFY|AMF_NOTIFY_ERR))) {
/* Found one */
if (dst != NULL) *dst = msgtable[src_ind].dst;
if (msg != NULL) *msg = msgtable[src_ind].msg;
if (err != NULL) *err = result;
/* Acknowledge error so it can be cleaned up upon next
* asynsend */
msgtable[src_ind].result = OK;
return(1);
}
}
}
return(0);
}