From 646be7194f9fd096ef22f52074cf9c03d595b6ec Mon Sep 17 00:00:00 2001
From: Jason Woofenden <jason@jasonwoof.com>
Date: Tue, 16 May 2017 16:11:51 -0400
Subject: [PATCH] add db_upgrade(), persistent_invalidate_cache()

---
 db.php         |   70 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 mutex.php      |   33 ++++++++++++++++++++++++++
 persistent.php |   19 ++++++++++-----
 3 files changed, 116 insertions(+), 6 deletions(-)
 create mode 100644 mutex.php

diff --git a/db.php b/db.php
index 5ac36a3..d24d8b6 100644
--- a/db.php
+++ b/db.php
@@ -535,3 +535,73 @@ function db_reposition($table, $row_id, $new_pos, $field = 'ord', $pretty = 'sam
 		return $prev_ord + round(($next_ord - $prev_ord) / 2);
 	}
 }
+
+# Call this to upgrade your database (using upgrade functions you define.)
+#
+# You can call this from config.php right after db_connect() to make sure the
+# database is up to date.
+#
+# When you want to update your schema, define a new function named
+# db_upgrade_to_X() where X is the next integer (start at 1).
+#
+# If there are any page views while your upgrade function is running, they will
+# stall until the upgrade function completes. This is often better than running
+# while the databse is in a transitional state, and is way way better than
+# running the upgrade function multiple times concurrently.
+#
+# Efficiency: this function is designed to be lean enough that you'd run it on
+# every page load, so you never forget to upgrade your schema after uploading
+# code changes. If your schema is up to date, this will only execute one
+# database query, and that query loads the persistent data store (used by
+# persistent_get()), so if you use that, you'll need that query to happen
+# anyway (giving this function a zero-query overhead).
+
+function db_upgrade() {
+	if (isset($GLOBALS['wfpl_persistent'])) {
+		$version = persistent_get('wfpl_db_version');
+	} else {
+		# custom version of persistent_init() that creates the table if needed
+		# instead of dying
+		$GLOBALS['wfpl_persistent'] = array();
+		_db_connection_needed();
+		$result = mysqli_query($GLOBALS['wfpl_db_handle'], 'select k,v from wfpl_persistent');
+		if ($result) {
+			while($row = mysqli_fetch_assoc($result)) {
+				$GLOBALS['wfpl_persistent'][$row['k']] = json_decode($row['v'], true);
+			} unset($row);
+			if (isset($GLOBALS['wfpl_persistent']['wfpl_db_version'])) {
+				$version = $GLOBALS['wfpl_persistent']['wfpl_db_version'];
+			} else {
+				$version = -1;
+			}
+		} else {
+			db_send_query('create table if not exists wfpl_persistent (k varchar(30) binary not null default "", v mediumblob, primary key (k)) CHARSET=utf8;');
+			$version = -1;
+		}
+	}
+
+	if ($version === -1) {
+		db_send_query('create table if not exists wfpl_mutexes (id int unique auto_increment, name varchar(30) binary, expires int(11)) CHARSET=utf8;');
+		$version = 0;
+		# don't save version now in case another thread is doing this too
+	}
+	$next = $version + 1;
+	if (function_exists("db_upgrade_to_$next")) {
+		require_once(__DIR__.'/'.'persistent.php');
+		require_once(__DIR__.'/'.'mutex.php');
+		mutex_lock('wfpl_db_upgrade', 20);
+		# check version again, in case another thread upgraded the database
+		# while we waited for a lock just now
+		persistent_invalidate_cache();
+		$version = persistent_get('wfpl_db_version');
+		if ($version === null) {
+			$version = 0;
+		}
+
+		for ($next = $version + 1; function_exists("db_upgrade_to_$next"); ++$next) {
+			call_user_func("db_upgrade_to_$next");
+			persistent_set('wfpl_db_version', $next);
+		}
+		mutex_unlock('wfpl_db_upgrade');
+	}
+}
diff --git a/mutex.php b/mutex.php
new file mode 100644
index 0000000..f6f4672
--- /dev/null
+++ b/mutex.php
@@ -0,0 +1,33 @@
+<?php
+
+function mutex_lock ($name, $duration) {
+	while (true) {
+		$now = time();
+		$deleted_obsoletes = false;
+		db_insert('wfpl_mutexes', 'name,expires', $name, $now + $duration);
+		$id = db_auto_id();
+		$rows = db_get_assocs('wfpl_mutexes', 'id,name,expires', 'order by id');
+		$first_match = true;
+		foreach ($rows as $row) {
+			if ($row['expires'] < $now) {
+				if (!$deleted_obsoletes) {
+					db_delete('wfpl_mutexes', 'where expires < %i', $now);
+					$deleted_obsoletes = true;
+				}
+			} elseif ($row['name'] === $name) {
+				if ($row['id'] == $id) {
+					return $id;
+				} else {
+					break;
+				}
+			}
+		}
+		# not first
+		db_delete('wfpl_mutexes', 'where id=%i', $id);
+		sleep(1);
+	}
+}
+
+function mutex_unlock ($id) {
+	db_delete('wfpl_mutexes', 'where id=%i', $id);
+}
diff --git a/persistent.php b/persistent.php
index 17005b6..c471322 100644
--- a/persistent.php
+++ b/persistent.php
@@ -5,19 +5,20 @@
 # 1.0 Universal public domain dedication, which can be found at
 # http://creativecommons.org/publicdomain/zero/1.0/
 
-# a simple, persistent, key/value store optimized for many reads
+# a simple, persistent, key/value store optimized for many reads and small data
 #
 # call persistent_{get,set,clear}
 
 # for internal use
+# IF YOU CHANGE THIS: change the version in db_upgrade() too
 function persistent_init() {
 	if (isset($GLOBALS['wfpl_persistent'])) {
 		return;
 	}
 	$GLOBALS['wfpl_persistent'] = array();
-	$rows = db_get_rows('persistent', 'k,v');
+	$rows = db_get_assocs('wfpl_persistent', 'k,v');
 	foreach ($rows as &$row) {
-		$GLOBALS['wfpl_persistent'][$row[0]] = json_decode($row[1], true);
+		$GLOBALS['wfpl_persistent'][$row['k']] = json_decode($row['v'], true);
 	} unset($row);
 }
 
@@ -34,10 +35,8 @@ function persistent_set($k, $v) {
 		if ($GLOBALS['wfpl_persistent'][$k] === $v) {
 			return;
 		}
-		db_update('persistent', 'v', json_encode($v), 'where k=%"', $k);
-	} else {
-		db_insert('persistent', 'k,v', $k, json_encode($v));
 	}
+	db_replace('wfpl_persistent', 'k,v', $k, json_encode($v));
 	$GLOBALS['wfpl_persistent'][$k] = $v;
 }
 function persistent_clear($k) {
@@ -47,3 +46,11 @@ function persistent_clear($k) {
 		unset($GLOBALS['wfpl_persistent'][$k]);
 	}
 }
+
+function persistent_invalidate_cache() {
+	if (isset($GLOBALS['wfpl_persistent'])) {
+		unset($GLOBALS['wfpl_persistent']);
+	}
+	return;
+}
+
-- 
1.7.10.4