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CriticalSectionProvider.php
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CriticalSectionProvider.php
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<?php
namespace Wikimedia\RequestTimeout;
/**
* A class providing a named critical section concept. When the code is inside
* a critical section, if a request timeout occurs, it is queued and then
* delivered when the critical section exits.
*
* The class stores configuration for "emergency timeouts". This is a second
* timeout which limits the amount of time a critical section may be open.
*/
class CriticalSectionProvider {
/** @var RequestTimeout */
private $requestTimeout;
/** @var float */
private $emergencyLimit;
/** @var callable|null */
private $emergencyCallback;
/** @var callable|null */
private $implicitExitCallback;
/** @var array */
private $stack = [];
/**
* @internal Use RequestTimeout::createCriticalSectionProvider()
*
* @param RequestTimeout $requestTimeout The parent object
* @param float $emergencyLimit The emergency timeout in seconds
* @param callable|null $emergencyCallback A callback to call when the
* emergency timeout expires. If null, an exception will be thrown.
* @param callable|null $implicitExitCallback A callback to call when a scoped
* critical section is exited implicitly by scope destruction, rather than
* by CriticalSectionScope::exit().
*/
public function __construct(
RequestTimeout $requestTimeout,
$emergencyLimit,
$emergencyCallback,
$implicitExitCallback
) {
$this->requestTimeout = $requestTimeout;
$this->emergencyLimit = $emergencyLimit;
$this->emergencyCallback = $emergencyCallback;
$this->implicitExitCallback = $implicitExitCallback;
}
/**
* Enter a critical section, giving it a name. The name should uniquely
* identify the calling code.
*
* Multiple critical sections may be active at a given time. Critical
* sections created by this method must be exited in the reverse order to
* which they were created, i.e. there is a stack of named critical
* sections.
*
* @param string $name
* @param float|null $emergencyLimit If non-null, this will override the
* configured emergency timeout
* @param callable|null $emergencyCallback If non-null, this will override
* the configured emergency timeout callback.
*/
public function enter( $name, $emergencyLimit = null, $emergencyCallback = null ) {
$id = $this->requestTimeout->enterCriticalSection(
$name,
$emergencyLimit ?? $this->emergencyLimit,
$emergencyCallback ?? $this->emergencyCallback
);
$this->stack[ count( $this->stack ) ] = [
'name' => $name,
'id' => $id
];
}
/**
* Exit a named critical section. If the name does not match the most recent
* call to enter(), an exception will be thrown.
*
* @throws CriticalSectionMismatchException
* @throws TimeoutException
* @param string $name
*/
public function exit( $name ) {
$i = count( $this->stack ) - 1;
if ( $i === -1 ) {
throw new CriticalSectionMismatchException( $name, '[none]' );
}
if ( $this->stack[$i]['name'] !== $name ) {
throw new CriticalSectionMismatchException( $name, $this->stack[$i]['name'] );
}
$this->requestTimeout->exitCriticalSection( $this->stack[$i]['id'] );
unset( $this->stack[$i] );
}
/**
* Enter a critical section, and return a scope variable. The critical
* section will automatically exit when the scope variable is destroyed.
*
* Multiple critical sections may be active at a given time. There is no
* restriction on the order in which critical sections created by this
* method are exited.
*
* NOTE: Callers should typically call CriticalSectionScope::exit() instead
* of waiting for __destruct() to be called, since exiting a critical
* section may throw a timeout exception, but it is a fatal error to throw
* an exception from a destructor during request shutdown.
*
* @param string $name A name for the critical section, used in error messages
* @param float|null $emergencyLimit If non-null, this will override the
* configured emergency timeout
* @param callable|null $emergencyCallback If non-null, this will override
* the configured emergency timeout callback.
* @param callable|null $implicitExitCallback If non-null, this will override
* the configured implicit exit callback. The callback will be called if the
* section is exited in __destruct() instead of by calling exit().
* @return CriticalSectionScope
*/
public function scopedEnter( $name, $emergencyLimit = null,
$emergencyCallback = null, $implicitExitCallback = null
) {
$id = $this->requestTimeout->enterCriticalSection(
$name,
$emergencyLimit ?? $this->emergencyLimit,
$emergencyCallback ?? $this->emergencyCallback
);
return new CriticalSectionScope(
$id,
function ( $id ) {
$this->requestTimeout->exitCriticalSection( $id );
},
$implicitExitCallback ?? $this->implicitExitCallback
);
}
/**
* Get the configured emergency time limit
*
* @since 1.1.0
* @return float
*/
public function getEmergencyLimit() {
return $this->emergencyLimit;
}
}

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