wikimedia / mediawiki

			$value = call_user_func( $callback, $this, $key, $currentValue, $exptime );

			$this->clearLastError();

			if ( $value === false ) {

				$success = true; // do nothing

			} elseif ( $currentValue === false ) {

				// Try to create the key, failing if it gets created in the meantime

				$success = $this->add( $key, $value, $exptime );

			} else {

				// Try to update the key, failing if it gets changed in the meantime

				$success = $this->cas( $casToken, $key, $value, $exptime );

			}

			if ( $this->getLastError() ) {

				return false; // IO error; don't spam retries

			}

		if ( $this->getLastError() ) {

			$success = false;

		} else {

			// Derive the new value from the old value

			$value = call_user_func( $callback, $this, $key, $currentValue, $exptime );

			if ( $value === false ) {

				$success = true; // do nothing

			} else {

				$success = $this->set( $key, $value, $exptime, $flags ); // set the new value

			}

		}

		if ( !$this->unlock( $key ) ) {

			// this should never happen