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Cache IsMe() results for process lifetime to avoid netlink contention #140

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Cache IsMe() results for process lifetime to avoid netlink contention #140

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53 changes: 45 additions & 8 deletions conserver/cutil.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2057,18 +2057,41 @@ ProbeInterfaces(in_addr_t bindAddr)
}
#endif /* USE_IPV6 */

/* IsMe() is called once per console per process per reread.
* getifaddrs()/freeifaddrs() every call, which thrashes the global
* netlink_table_lock Therefore we cache, WARNING: caches results
* for process lifetime though
*/
#define ISME_CACHE_SIZE 256
static struct {
char *name;
int result;
} isme_result_cache[ISME_CACHE_SIZE];
static int isme_result_cache_count = 0;
#if USE_IPV6
static struct ifaddrs *isme_cached_addrs = (struct ifaddrs *)0;
static int isme_addrs_initialized = 0;
#endif

int
IsMe(char *id)
{
#if USE_IPV6
int ret = 0;
int error;
int i;
struct addrinfo hints;
struct addrinfo *res, *rp;
struct ifaddrs *myAddrs, *ifa;
struct ifaddrs *ifa;
void *a, *b;
size_t len;

/* hostname memo: most consoles share a handful of master names */
for (i = 0; i < isme_result_cache_count; i++) {
if (strcmp(isme_result_cache[i].name, id) == 0)
return isme_result_cache[i].result;
}

memset(&hints, 0, sizeof(hints));
hints.ai_family = PF_UNSPEC;

Expand All @@ -2079,15 +2102,19 @@ IsMe(char *id)
return 0;
}

/* get list of all addresses on system */
error = getifaddrs(&myAddrs);
if (error) {
perror("getifaddrs failed");
return 0;
/* get list of all addresses on system (cached for process lifetime) */
if (!isme_addrs_initialized) {
error = getifaddrs(&isme_cached_addrs);
if (error) {
perror("getifaddrs failed");
freeaddrinfo(res);
return 0;
}
isme_addrs_initialized = 1;
}

/* try to find a match */
for (ifa = myAddrs; ifa != NULL; ifa = ifa->ifa_next) {
for (ifa = isme_cached_addrs; ifa != NULL; ifa = ifa->ifa_next) {
/* skip interfaces without address or in down state */
if (ifa->ifa_addr == NULL || !(ifa->ifa_flags & IFF_UP))
continue;
Expand Down Expand Up @@ -2122,8 +2149,18 @@ IsMe(char *id)

done:
freeaddrinfo(res);
freeifaddrs(myAddrs);
/* NB: isme_cached_addrs is process-lifetime; do NOT freeifaddrs */
CONDDEBUG((1, "IsMe: ret %d id %s", ret, id));

/* memoize so next call skips both getaddrinfo and the inner loop */
if (isme_result_cache_count < ISME_CACHE_SIZE) {
char *dup = StrDup(id);
if (dup != (char *)0) {
isme_result_cache[isme_result_cache_count].name = dup;
isme_result_cache[isme_result_cache_count].result = ret;
isme_result_cache_count++;
}
}
return ret;
#else
int j, i;
Expand Down