Here is a simple Mutex class implementation, using semaphore on Linux and flock on windows.
Filename is optionnal, but you can provide it anyway. This way the file will be created on windows, not on linux as it is not needed.
It's fast written and certainly lacks error checking code.
<?php
class Mutex
{
private $id;
private $sem_id;
private $is_acquired = false;
private $is_windows = false;
private $filename = '';
private $filepointer;
function __construct()
{
if(substr(PHP_OS, 0, 3) == 'WIN')
$this->is_windows = true;
}
public function init($id, $filename = '')
{
$this->id = $id;
if($this->is_windows)
{
if(empty($filename)){
print "no filename specified";
return false;
}
else
$this->filename = $filename;
}
else
{
if(!($this->sem_id = sem_get($this->id, 1))){
print "Error getting semaphore";
return false;
}
}
return true;
}
public function acquire()
{
if($this->is_windows)
{
if(($this->filepointer = @fopen($this->filename, "w+")) == false)
{
print "error opening mutex file<br>";
return false;
}
if(flock($this->filepointer, LOCK_EX) == false)
{
print "error locking mutex file<br>";
return false;
}
}
else
{
if (! sem_acquire($this->sem_id)){
print "error acquiring semaphore";
return false;
}
}
$this->is_acquired = true;
return true;
}
public function release()
{
if(!$this->is_acquired)
return true;
if($this->is_windows)
{
if(flock($this->filepointer, LOCK_UN) == false)
{
print "error unlocking mutex file<br>";
return false;
}
fclose($this->filepointer);
}
else
{
if (! sem_release($this->sem_id)){
print "error releasing semaphore";
return false;
}
}
$this->is_acquired = false;
return true;
}
public function getId()
{
return $this->sem_id;
}
}
?>
Example use:
<?php
$mutex = new Mutex();
$mutex->init(1, "mutex_file.txt");
$mutex->acquire();
//Whatever you want single-threaded here...
$mutex->release();
?>
CXLVI. セマフォ・共有メモリおよび IPC 関数(semaphore)
導入
このモジュールは、System V IPC 関連の関数へのラッパーを提供します。 セマフォ・共有メモリおよびプロセス間通信(IPC)がその中に含まれます。
セマフォは、マシーン上のリソースへの排他的アクセス機能や、 同時にあるリソースを使用することができるプロセスの数を制限するために 使用することができます。
このモジュールは、System V 共有メモリを使用した共有メモリ関数も 提供します。共有メモリは、グローバル変数へのアクセス手段を提供するために 使用することが可能です。別の httpd デーモンおよび (Perl, C, ... のような)他のプログラムさえ、グローバルデータ交換を 提供するこのデータにアクセスすることが可能です。 共有メモリは、同時アクセスに関して安全ではないということを覚えておいて ください。 同期をとるには、セマフォを使用してください。
表 273. Unix OS による共有メモリの制限
| SHMMAX | 共有メモリの最大サイズ。通常は 131072 バイト |
| SHMMIN | 共有メモリの最小サイズ。通常は 1 バイト |
| SHMMNI | 共有メモリセグメントの最大数。通常は 100 |
| SHMSEG | プロセス毎の共有メモリの最大数。通常は 6 |
メッセージング関数は、他のプロセスと相互にメッセージを送受信する ために使用することができます。 これにより簡単で効率的なプロセス間のデータ交換が可能であり、 Unix ドメインソケットを用いる場合のような設定は不要です。
注意: この拡張モジュールは Windows 環境では利用できません。
要件
外部ライブラリを必要としません。
インストール手順
この関数はデフォルトでは有効になってはいません。System V セマフォの サポートを有効にするには、オプション --enable-sysvsem を指定して PHP を コンパイルする必要があります。System V 共有メモリのサポートを有効にするには、 オプション --enable-sysvshm を 指定して PHP をコンパイルする必要があります。System V メッセージを有効に するには、オプション --enable-sysvmsg を指定して PHP をコンパイル します。
実行時設定
php.ini の設定により動作が変化します。
PHP_INI_* 定数の詳細および定義については 付録 I. php.ini ディレクティブ を参照してください。
リソース型
定義済み定数
以下の定数が定義されています。 この関数の拡張モジュールが PHP 組み込みでコンパイルされているか、 実行時に動的にロードされている場合のみ使用可能です。
目次
- ftok — パス名とプロジェクト ID を、System V IPC キーに変換する
- msg_get_queue — メッセージキューを作成またはそれにアタッチする
- msg_receive — メッセージキューからメッセージを受信する
- msg_remove_queue — メッセージキューを破棄する
- msg_send — メッセージキューにメッセージを送信する
- msg_set_queue — メッセージキューデータ構造体の情報を設定する
- msg_stat_queue — メッセージキューデータ構造体の情報を返す
- sem_acquire — セマフォを得る
- sem_get — セマフォ ID を得る
- sem_release — セマフォを解放する
- sem_remove — セマフォを削除する
- shm_attach — 共有メモリセグメントを作成またはオープンする
- shm_detach — 共有メモリセグメントへの接続を閉じる
- shm_get_var — 共有メモリから変数を返す
- shm_put_var — 共有メモリの変数を挿入または更新する
- shm_remove_var — 共有メモリから変数を削除する
- shm_remove — Unix システムから共有メモリを削除する
セマフォ・共有メモリおよび IPC 関数(semaphore)
mr dot smaon at gmail dot com
26-Jan-2007 02:08
26-Jan-2007 02:08
hekkwan at gmail dot com
14-Nov-2006 11:15
14-Nov-2006 11:15
I have been trying to get a php console script and a C application to use a common semaphore for a while. I just got it working, so I thought Id paste the code here incase anyone needs to do this, however, this is not the place for long code examples
I used c code from the php implementation to set up the semaphore set and then mimic the way the php interpreter implements a mutext type locking scheme, using a common semop call.
One has to do the process in the same way as its done in the php implementation, otherwise you run the risk of the php interpreter resetting the semaphore set for you.
The basic idea is.
1) sem_get - use a three semaphore set
1.1) increment the first sem
1.2) check the usage count (sem 3), if only one, set the max_attach using sem 2 for mutex behaviour to sem 3
2) decrement sem 1
3) for locking / unlocking use the first semaphore, but always call the above from your c-code.
If you want a copy of my code, email me and I'll happily send it to you !
chrissavery at removeme dot gmail dot com
03-Jun-2006 05:18
03-Jun-2006 05:18
I was confused by two things that caused strange behaviour in my use of semaphores with php scripts running under apache.
Often enough page requests will end up being filled by the same process as other simultaneous requests. So semaphores will block when you may not have expected.
Also note that sem_remove() will remove it for all processes, not just the calling one. So you have to be sure that the last process running removes the semaphore and none before. I thought there was some failures occurring when my child processes were dropping out with errors.
So you can't just use get, acquire, release, remove in one script that will be hit by a web user. (1) They may end up in the same process and will wait on the other, and (2) the first one to finish will destroy the semaphore for others.
I left out the remove call, and it works ok, but I still wonder if the semaphore is removed by php when the last script that did a get finishes? Also creating a child process to do the work using proc_open works to ensure seperate processes but to be careful you would want to limit the number somehow as well.
Denis Gerasimov
02-Nov-2005 09:19
02-Nov-2005 09:19
Many (most?) developers use Win32 platform for PHP Web applications development while production servers mostly run Unix/Linux OS. Below is the stub code I use to make it possible to write scripts on Win32 that use semaphores:
<?php
if (substr(PHP_OS, 0, 3) == 'WIN') { // if Windows OS detected
function ftok($pathname, $proj)
{
if (empty($pathname) || !file_exists($pathname)) { // an error occured
return -1;
}
$pathname = $pathname . (string) $proj;
$key = array();
while (sizeof($key) < strlen($pathname)) {
$key[] = ord(substr($pathname, sizeof($key), 1));
}
return dechex(array_sum($key));
}
function sem_acquire($sem_identifier)
{
return true;
}
function sem_get($key, $max_acquire = null, $perm = null, $auto_release = null)
{
return true;
}
function sem_release($sem_identifier)
{
return true;
}
function sem_remove($sem_identifier)
{
return true;
}
}
?>
Of course, there is no way to test semaphores until you have no Unix/Linux test server.
p4nzer at yahoo dot com
01-Nov-2005 10:55
01-Nov-2005 10:55
Actually, the way to lock a semaphore from C code appears to be:
<?
struct sembuf semptr[2];
if( (semid = semget(SEM_KEY, PHP_SEM_NEED_NUMBER, 0666 | IPC_CREAT)) < 0 ) {
perror("semget");
return 1;
}
semptr[0].sem_num = 0;
semptr[0].sem_op = -1;
semptr[0].sem_flg = SEM_UNDO;
semptr[1].sem_num = 1;
semptr[1].sem_op = 1;
semptr[1].sem_flg = SEM_UNDO;
if( semop(semid, &semptr[0], 2) < 0 ) {
perror("semop");
}
?>
PS: Disregard the <? and ?>, it's just for pretty printing... this is C code!
05-Feb-2004 01:25
Here is an article/tutorial on the subject:
http://www.php-mag.net/itr/online_artikel/psecom,id,448,nodeid,114
hcuevas at galenicom dot com
23-Oct-2003 11:49
23-Oct-2003 11:49
Don't use semaphores to serialize access to an undefined number of resources. There is no way (yet) to know before locking if a semaphore is already locked, thus not being able to fully release the semaphore and occupying a semaphore resource for an undefined time.
A possible solution is to build a shared mem pool and store there the current number of locks for a semaphore id.
Cheers,
Horaci Cuevas
david () php net
09-Jul-2003 05:45
09-Jul-2003 05:45
Here is a quick utility to dump the contents of a shm_ format memory segment:
http://www.davidc.net/php/shm/
Roman Laptev <tmp at laptev dot org>
02-Apr-2003 11:50
02-Apr-2003 11:50
If you going to work with semaphore, which was created by some external program, you can try the following code for this program (C example):
#define SVSEM_MODE (SEM_R | SEM_A | SEM_R>>3 | SEM_R>>6) /* 0644 */
#define PHP_SEM_NEED_NUMBER 3
/*.......*/
int semid, semflag = SVSEM_MODE | IPC_CREAT | IPC_EXCL;
struct sembuf semptr;
union semun semopts;
/*.......*/
if( (semid = semget(sempath, PHP_SEM_NEED_NUMBER, semflag)) >= 0 ) {
semopts.val = 1; /* initial value for sem */
if( semctl( semid, 0, SETVAL, semopts) < 0 ) {/*error*/}
if( semctl( semid, 1, SETVAL, semopts) < 0 ) {/*error*/}
/* PHP wanna zero for its own semget at third sem.
* look at ./PHP_SOURCE_PATH/ext/sysvsem/sysvsem.c
*/
semopts.val = 0;
if( semctl( semid, 2, SETVAL, semopts) < 0 ) {/*error*/}
}
else if(errno == EEXIST) { /* connect only */
if( (semid = semget(sempath, PHP_SEM_NEED_NUMBER, SVSEM_MODE | IPC_CREAT)) < 0 ) {/*error*/}
}
else {/*error*/}
/*.......*/
/* If you want acquire the sem */
semptr.sem_num = 0;
semptr.sem_op = -1; /* lock it */
semptr.sem_flg = SEM_UNDO;
while( semop(semid, &semptr, 1) < 0 ) {/*error*/}
/*.......*/
Thanks,
Roma
elran70 at hotmail dot com
23-Jun-2002 02:54
23-Jun-2002 02:54
Samlpe code for using most of the functions here:
$MEMSIZE = 512;// size of shared memory to allocate
$SEMKEY = 1; // Semaphore key
$SHMKEY = 2; // Shared memory key
echo "Start.\n";
// Get semaphore
$sem_id = sem_get($SEMKEY, 1);
if ($sem_id === false)
{
echo "Fail to get semaphore";
exit;
}
else
echo "Got semaphore $sem_id.\n";
// Accuire semaphore
if (! sem_acquire($sem_id))
{
echo "Fail to aquire semaphore $sem_id.\n";
sem_remove($sem_id);
exit;
}
else
echo "Success aquire semaphore $sem_id.\n";
$shm_id = shm_attach($SHMKEY, $MEMSIZE);
if ($shm_id === false)
{
echo "Fail to attach shared memory.\n";
sem_remove($sem_id);
exit;
}
else
echo "Success to attach shared memory : $shm_id.\n";
// Write variable 1
if (!shm_put_var($shm_id, 1, "Variable 1"))
{
echo "Fail to put var 1 on shared memory $shm_id.\n";
sem_remove($sem_id);
shm_remove ($shm_id);
exit;
}
else
echo "Write var1 to shared memory.\n";
// Write variable 2
if (!shm_put_var($shm_id, 2, "Variable 2"))
{
echo "Fail to put var 2 on shared memory $shm_id.\n";
sem_remove($sem_id);
shm_remove ($shm_id);
exit;
}
else
echo "Write var2 to shared memory.\n";
// Read variable 1
$var1 = shm_get_var ($shm_id, 1);
if ($var1 === false)
{
echo "Fail to retrive Var 1 from Shared memory $shm_id, return value=$var1.\n";
}
else
echo "Read var1=$var1.\n";
// Read variable 1
$var2 = shm_get_var ($shm_id, 2);
if ($var1 === false)
{
echo "Fail to retrive Var 2 from Shared memory $shm_id, return value=$var2.\n";
}
else
echo "Read var2=$var2.\n";
// Release semaphore
if (!sem_release($sem_id))
echo "Fail to release $sem_id semaphore.\n";
else
echo "Semaphore $sem_id released.\n";
// remove shared memory segmant from SysV
if (shm_remove ($shm_id))
echo "Shared memory successfully removed from SysV.\n";
else
echo "Fail to remove $shm_id shared memory from SysV.\n";
// Remove semaphore
if (sem_remove($sem_id))
echo "semaphore removed successfully from SysV.\n";
else
echo "Fail to remove $sem_id semaphore from SysV.\n";
echo "End.\n";
mikew at php dot net
01-Jun-2001 01:46
01-Jun-2001 01:46
As for security, please look at the perm argument to shm_get. Shared Memory blocks has the same permission semantics as unix user/group/other file permissions. As long as your webserver is running as a user that no other users can script to.. and as long as the permissions are set to 600, you should be fine and have no security concerns.
php at stolt dot de
21-Sep-2000 03:58
21-Sep-2000 03:58
The integer keys for sem_get() and shm_attach() have to be systemwide unique. There is no method to ensure that no other process on the system will use your specific key (security! and possible malfunction). Also shared memory is very seldom used there are possibilities for conflicts! To see the used id's you can use the program 'ipcs' (at least under SuseLinux;) ). Thanks Christian C.