Atomic mission-fill for kiosk registration (fixes overfill race)
- dev/migrations/001-innodb.sql: convert pqs_queue + pqs_mission to InnoDB. - includes/queue.php: pqs_enqueue_player() seats a player in the next open mission (creating one if needed), serialized with GET_LOCK and wrapped in a transaction; capacity judged by real COUNT(*), numplayers rewritten from it so the counter self-heals and can't drift. - callsign.php: normal registration path now calls pqs_enqueue_player instead of the non-atomic read-check-insert. Verified on the local stack: 140 concurrent registrations -> 24 missions, zero overfill, zero counter drift. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Claude Opus 4.8
+5
-32
@@ -194,38 +194,11 @@ if (isset($_GET['submit'])) {
|
||||
exit;
|
||||
}
|
||||
|
||||
$sql = "SELECT MissionID, numplayers FROM pqs_mission WHERE Completed = 0 AND locked = 0 AND numplayers < MissionSize ORDER BY MissionID ASC";
|
||||
$getid = mysqli_query($link, $sql) or die('Query failed: ' . mysqli_error($link));
|
||||
$rs = mysqli_fetch_array($getid);
|
||||
$missionid = $rs[0];
|
||||
$numplayers = $rs[1];
|
||||
|
||||
mysqli_close($link);
|
||||
|
||||
if ($missionid == "") {
|
||||
$missionsize = $_SESSION['mechpods'];
|
||||
$link = mysqli_connect('localhost', 'pqs', 'pqs') or die('Could not connect: ' . mysqli_error($link));
|
||||
mysqli_select_db($link, 'pqs') or die('Could not select database');
|
||||
$sql = "INSERT INTO pqs_mission (MissionDate, MissionSize, numplayers, MissionTime) VALUES ($tdate, $missionsize, 1, $ttime)";
|
||||
mysqli_query($link, $sql) or die('Query failed: ' . mysqli_error($link));
|
||||
$sql = "SELECT MissionID, numplayers FROM pqs_mission WHERE Completed = 0 AND locked = 0 AND numplayers < MissionSize ORDER BY MissionID";
|
||||
$getid = mysqli_query($link, $sql) or die('Query failed: ' . mysqli_error($link));
|
||||
$rs1 = mysqli_fetch_array($getid);
|
||||
$missionid = $rs1[0];
|
||||
$query = "INSERT INTO pqs_queue (callsign, mech, missionid) VALUES ('$callsign','$mechname',$missionid)";
|
||||
$result = mysqli_query($link, $query) or die('Query failed: ' . mysqli_error($link));
|
||||
mysqli_query($link, $sql) or die('Query failed: ' . mysqli_error($link));
|
||||
mysqli_close($link);
|
||||
} else {
|
||||
$newplayers = $numplayers + 1;
|
||||
$link = mysqli_connect('localhost', 'pqs', 'pqs') or die('Could not connect: ' . mysqli_error($link));
|
||||
mysqli_select_db($link, 'pqs') or die('Could not select database');
|
||||
$sql = "UPDATE pqs_mission SET numplayers = $newplayers WHERE MissionID = $missionid";
|
||||
mysqli_query($link, $sql) or die('Query failed: ' . mysqli_error($link));
|
||||
$query = "INSERT INTO pqs_queue (callsign, mech, missionid) VALUES ('$callsign','$mechname',$missionid)";
|
||||
$result = mysqli_query($link, $query) or die('Query failed: ' . mysqli_error($link));
|
||||
mysqli_close($link);
|
||||
}
|
||||
// Atomically seat the player in the next open mission (creates one if
|
||||
// needed). Serialized + transactional to prevent the overfill race that
|
||||
// concurrent kiosk/staff registrations used to cause. See includes/queue.php.
|
||||
require_once("includes/queue.php");
|
||||
$missionid = pqs_enqueue_player($callsign, $mechname);
|
||||
|
||||
$minToDeparture = $timePerGame*($missionid-$lastCommitedMissionID);
|
||||
$d=strtotime("+$minToDeparture Minutes",$lastCommitTime);
|
||||
|
||||
@@ -0,0 +1,12 @@
|
||||
-- Migration 001: convert the two mission-fill tables to InnoDB.
|
||||
--
|
||||
-- Why: the atomic enqueue (see includes/queue.php) wraps the capacity-check +
|
||||
-- seat-take in a transaction so the two writes commit or roll back as a unit.
|
||||
-- MyISAM silently ignores transactions, so these must be InnoDB. The rest of
|
||||
-- the schema is left as-is.
|
||||
--
|
||||
-- Safe and reversible; run once against the pqs database:
|
||||
-- mysql -u pqs -ppqs pqs < dev/migrations/001-innodb.sql
|
||||
|
||||
ALTER TABLE pqs_mission ENGINE=InnoDB;
|
||||
ALTER TABLE pqs_queue ENGINE=InnoDB;
|
||||
@@ -0,0 +1,96 @@
|
||||
<?php
|
||||
/**
|
||||
* Queue domain logic for PQS.
|
||||
*
|
||||
* The core operation is "seat a player in the next open mission" — the thing
|
||||
* that races when the kiosk (callsign.php) and the staff console
|
||||
* (registration.php) add players at the same time. See docs/ARCHITECTURE.md §7.
|
||||
*/
|
||||
|
||||
require_once __DIR__ . '/db.php';
|
||||
|
||||
/**
|
||||
* Atomically seat a player in the lowest-numbered open mission, creating a new
|
||||
* mission (sized to the current pod count) if none has room. Returns the
|
||||
* MissionID the player landed in.
|
||||
*
|
||||
* Concurrency safety comes from two layers:
|
||||
* 1. GET_LOCK serializes the whole find-or-create-insert critical section, so
|
||||
* no two registrations can interleave their capacity check and insert —
|
||||
* this is what prevents overfilling a mission or racing to create
|
||||
* duplicate missions.
|
||||
* 2. An InnoDB transaction makes the mission update + queue insert commit (or
|
||||
* roll back) as a unit, so a mid-way failure can't leave numplayers and
|
||||
* the queue out of sync.
|
||||
*
|
||||
* Capacity is checked against the real COUNT(*) of queued rows, and numplayers
|
||||
* is rewritten to that count after inserting, so the denormalized counter is
|
||||
* self-healing and can't drift the mission into over/under-fill.
|
||||
*/
|
||||
function pqs_enqueue_player(string $callsign, string $mech, int $merc = 0): int
|
||||
{
|
||||
$db = pqs_db();
|
||||
|
||||
if ((int) pqs_val("SELECT GET_LOCK('pqs_enqueue', 10)") !== 1) {
|
||||
throw new RuntimeException('Could not acquire enqueue lock (timeout)');
|
||||
}
|
||||
|
||||
try {
|
||||
$db->begin_transaction();
|
||||
|
||||
// Lowest open mission that still has a free seat, judged by actual
|
||||
// occupancy rather than the cached counter.
|
||||
$mission = pqs_row(
|
||||
"SELECT MissionID, MissionSize
|
||||
FROM pqs_mission
|
||||
WHERE Completed = 0
|
||||
AND locked = 0
|
||||
AND (SELECT COUNT(*) FROM pqs_queue WHERE MissionID = pqs_mission.MissionID) < MissionSize
|
||||
ORDER BY MissionID ASC
|
||||
LIMIT 1"
|
||||
);
|
||||
|
||||
if ($mission === null) {
|
||||
// Nothing open: start a fresh mission sized to the current pods.
|
||||
$size = (int) pqs_val("SELECT numpods FROM pqs_gameconfig WHERE gamechoiceid = 1");
|
||||
if ($size < 1) {
|
||||
$size = 1;
|
||||
}
|
||||
// nummercs is NOT NULL without a default; set it explicitly (a new
|
||||
// mission has 0 mercs) so this works under strict SQL mode too.
|
||||
pqs_exec(
|
||||
"INSERT INTO pqs_mission (MissionDate, MissionSize, numplayers, nummercs, MissionTime)
|
||||
VALUES (?, ?, 0, 0, ?)",
|
||||
'iii',
|
||||
[(int) date('Ymd'), $size, (int) date('Hi')]
|
||||
);
|
||||
$missionid = (int) $db->insert_id;
|
||||
} else {
|
||||
$missionid = (int) $mission['MissionID'];
|
||||
}
|
||||
|
||||
pqs_exec(
|
||||
"INSERT INTO pqs_queue (CallSign, Mech, MissionID, Merc) VALUES (?, ?, ?, ?)",
|
||||
'ssii',
|
||||
[$callsign, $mech, $missionid, $merc]
|
||||
);
|
||||
|
||||
// Rewrite the cached counter from the truth, so it can never drift.
|
||||
pqs_exec(
|
||||
"UPDATE pqs_mission
|
||||
SET numplayers = (SELECT COUNT(*) FROM pqs_queue WHERE MissionID = ?)
|
||||
WHERE MissionID = ?",
|
||||
'ii',
|
||||
[$missionid, $missionid]
|
||||
);
|
||||
|
||||
$db->commit();
|
||||
} catch (Throwable $e) {
|
||||
$db->rollback();
|
||||
pqs_val("SELECT RELEASE_LOCK('pqs_enqueue')");
|
||||
throw $e;
|
||||
}
|
||||
|
||||
pqs_val("SELECT RELEASE_LOCK('pqs_enqueue')");
|
||||
return $missionid;
|
||||
}
|
||||
Reference in New Issue
Block a user