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lvmetad: Update retry logic vars and comments.

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Avoid using variables with same name as functions.
Use lvm_even_rand for random numbers.
This commit is contained in:
Alasdair G Kergon 2014-04-04 01:46:53 +01:00
parent d36f721bb9
commit b38a3d8c85
1 changed files with 30 additions and 23 deletions
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53
lib/cache/lvmetad.c vendored
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@ -22,6 +22,9 @@
#include "format-text.h" // TODO for disk_locn, used as a DA representation #include "format-text.h" // TODO for disk_locn, used as a DA representation
#include "crc.h" #include "crc.h"
#define SCAN_TIMEOUT_SECONDS 80
#define MAX_RESCANS 10 /* Maximum number of times to scan all PVs and retry if the daemon returns a token mismatch error */
static daemon_handle _lvmetad; static daemon_handle _lvmetad;
static int _lvmetad_use = 0; static int _lvmetad_use = 0;
static int _lvmetad_connected = 0; static int _lvmetad_connected = 0;
@ -141,8 +144,10 @@ static daemon_reply _lvmetad_send(const char *id, ...)
va_list ap; va_list ap;
daemon_reply repl; daemon_reply repl;
daemon_request req; daemon_request req;
int try = 0; unsigned num_rescans = 0;
int time = 0, wait, sleep = 1; unsigned total_usecs_waited = 0;
unsigned max_remaining_sleep_times = 1;
unsigned wait_usecs;
retry: retry:
req = daemon_request_make(id); req = daemon_request_make(id);
@ -158,30 +163,32 @@ retry:
daemon_request_destroy(req); daemon_request_destroy(req);
/*
* If another process is trying to scan, it might have the
* same future token id and it's better to wait and avoid doing
* the work multiple times. For the case where the future token is
* different, the wait is randomized so that multiple waiting
* processes do not start scanning all at once.
*
* If the token is mismatched because of global_filter changes,
* we re-scan immediately, but if we lose the potential race for
* the update, we back off for a short while (0.05-0.5 seconds) and
* try again.
*/
if (!repl.error && !strcmp(daemon_reply_str(repl, "response", ""), "token_mismatch") && if (!repl.error && !strcmp(daemon_reply_str(repl, "response", ""), "token_mismatch") &&
try < 10 && time < 80000000 && !test_mode()) { num_rescans < MAX_RESCANS && total_usecs_waited < (SCAN_TIMEOUT_SECONDS * 1000000) && !test_mode()) {
/* if (!strcmp(daemon_reply_str(repl, "expected", ""), "update in progress") ||
* If another process is trying to scan, they might have the max_remaining_sleep_times) {
* same future token id and it's better to wait and avoid doing wait_usecs = 50000 + lvm_even_rand(&_lvmetad_cmd->rand_seed, 450000); /* between 0.05s and 0.5s */
* the work multiple times. For the case the future token is (void) usleep(wait_usecs);
* different, the wait is randomized so that multiple waiting total_usecs_waited += wait_usecs;
* processes do not start scanning all at once. if (max_remaining_sleep_times)
* max_remaining_sleep_times--; /* Sleep once before rescanning the first time, then 5 times each time after that. */
* If the token is mismatched because of global_filter changes,
* we re-scan immediately, but if we lose the potential race for
* the update, we back off for a short while (0.2-2 seconds) and
* try again.
*/
if (!strcmp(daemon_reply_str(repl, "expected", ""), "update in progress") || sleep) {
wait = 50000 + random() % 450000; /* 0.05 - 0.5s */
time += wait;
usleep( wait );
-- sleep;
} else { } else {
/* If the re-scan fails here, we try again later. */ /* If the re-scan fails here, we try again later. */
lvmetad_pvscan_all_devs(_lvmetad_cmd, NULL); (void) lvmetad_pvscan_all_devs(_lvmetad_cmd, NULL);
++ try; num_rescans++;
sleep = 5; max_remaining_sleep_times = 5;
} }
daemon_reply_destroy(repl); daemon_reply_destroy(repl);
goto retry; goto retry;