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MINOR: ring: reserve one special value for the readers count

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In order to support concurrent writers we'll need to lock areas in the
buffer. For this we'll use one special value of the single-byte readers
count. Let's reserve it now and use the macro instead of the hardcoded
255.
This commit is contained in:
Willy Tarreau 2023-02-20 19:21:52 +01:00
parent 0f611987da
commit 0b1c17a2dd
2 changed files with 7 additions and 3 deletions
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6
include/haproxy/ring-t.h
View File

@ -27,7 +27,7 @@
#include <haproxy/thread.h>
/* The code below handles circular buffers with single-producer and multiple
* readers (up to 255). The buffer storage area must remain always allocated.
* readers (up to 254). The buffer storage area must remain always allocated.
* It's made of series of payload blocks followed by a readers count (RC).
* There is always a readers count at the beginning of the buffer as well. Each
* payload block is composed of a varint-encoded size (VI) followed by the
@ -96,6 +96,10 @@
#define RING_WF_WAIT_MODE 0x00000001 /* wait for new contents */
#define RING_WF_SEEK_NEW 0x00000002 /* seek to new contents */
/* keep values below in decimal, they may be dumped in error messages */
#define RING_WRITING_SIZE 255 /* the next message's size is being written */
#define RING_MAX_READERS 254 /* highest supported value for RC */
struct ring {
struct buffer buf; // storage area
struct list waiters; // list of waiters, for now, CLI "show event"

4
src/ring.c
View File

@ -270,7 +270,7 @@ int ring_attach(struct ring *ring)
int users = ring->readers_count;
do {
if (users >= 255)
if (users >= RING_MAX_READERS)
return 0;
} while (!_HA_ATOMIC_CAS(&ring->readers_count, &users, users + 1));
return 1;
@ -313,7 +313,7 @@ int ring_attach_cli(struct ring *ring, struct appctx *appctx, uint flags)
if (!ring_attach(ring))
return cli_err(appctx,
"Sorry, too many watchers (255) on this ring buffer. "
"Sorry, too many watchers (" TOSTR(RING_MAX_READERS) ") on this ring buffer. "
"What could it have so interesting to attract so many watchers ?");
if (!appctx->io_handler)