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MDL-67075 session: Added extra debugging of blocking redis session locks

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This commit is contained in:
Brendan Heywood 2019-10-30 17:25:58 +11:00
parent 9df4a4de18
commit 7bc8ccdcf0
1 changed files with 33 additions and 13 deletions
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46
lib/classes/session/redis.php
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@ -339,7 +339,7 @@ class redis extends handler {
}
/**
* Obtain a session lock so we are the only one using it at the moent.
* Obtain a session lock so we are the only one using it at the moment.
*
* @param string $id The session id to lock.
* @return bool true when session was locked, exception otherwise.
@ -355,23 +355,43 @@ class redis extends handler {
* on the session for the entire time it is open. If another AJAX call, or page is using
* the session then we just wait until it finishes before we can open the session.
*/
// Store the current host, process id and the request URI so it's easy to track who has the lock.
$hostname = gethostname();
if ($hostname === false) {
$hostname = 'UNKNOWN HOST';
}
$pid = getmypid();
if ($pid === false) {
$pid = 'UNKNOWN';
}
$uri = isset($_SERVER['REQUEST_URI']) ? $_SERVER['REQUEST_URI'] : 'unknown uri';
$whoami = "[pid {$pid}] {$hostname}:$uri";
while (!$haslock) {
$haslock = $this->connection->setnx($lockkey, '1');
if (!$haslock) {
usleep(rand(100000, 1000000));
if ($this->time() > $startlocktime + $this->acquiretimeout) {
// This is a fatal error, better inform users.
// It should not happen very often - all pages that need long time to execute
// should close session immediately after access control checks.
error_log('Cannot obtain session lock for sid: '.$id.' within '.$this->acquiretimeout.
'. It is likely another page has a long session lock, or the session lock was never released.');
throw new exception("Unable to obtain session lock");
}
} else {
$haslock = $this->connection->setnx($lockkey, $whoami);
if ($haslock) {
$this->locks[$id] = $this->time() + $this->lockexpire;
$this->connection->expire($lockkey, $this->lockexpire);
return true;
}
if ($this->time() > $startlocktime + $this->acquiretimeout) {
// This is a fatal error, better inform users.
// It should not happen very often - all pages that need long time to execute
// should close session immediately after access control checks.
$whohaslock = $this->connection->get($lockkey);
// @codingStandardsIgnoreStart
error_log("Cannot obtain session lock for sid: $id within $this->acquiretimeout seconds. " .
"It is likely another page ($whohaslock) has a long session lock, or the session lock was never released.");
// @codingStandardsIgnoreEnd
throw new exception("Unable to obtain session lock");
}
usleep(rand(100000, 1000000));
}
}