Limit-number-of-concurrent-preview-generations

Signed-off-by: Bowen Ding <dbw9580@live.com>
Signed-off-by: szaimen <szaimen@e.mail.de>

1 files changed, 125 insertions, 20 deletions

diff --git a/lib/private/Preview/Generator.php b/lib/private/Preview/Generator.php
index a49cc8e522e..7d2408d683f 100644
--- a/lib/private/Preview/Generator.php
+++ b/lib/private/Preview/Generator.php
@@ -48,6 +48,8 @@ use Symfony\Component\EventDispatcher\EventDispatcherInterface;
 use Symfony\Component\EventDispatcher\GenericEvent;
 
 class Generator {
+	public const SEMAPHORE_ID_ALL = 0x0a11;
+	public const SEMAPHORE_ID_NEW = 0x07ea;
 
 	/** @var IPreview */
 	private $previewManager;
@@ -303,6 +305,98 @@ class Generator {
 	}
 
 	/**
+	 * Acquire a semaphore of the specified id and concurrency, blocking if necessary.
+	 * Return an identifier of the semaphore on success, which can be used to release it via
+	 * {@see Generator::unguardWithSemaphore()}.
+	 *
+	 * @param int $semId
+	 * @param int $concurrency
+	 * @return false|resource the semaphore on success or false on failure
+	 */
+	public static function guardWithSemaphore(int $semId, int $concurrency) {
+		if (!extension_loaded('sysvsem')) {
+			return false;
+		}
+		$sem = sem_get($semId, $concurrency);
+		if ($sem === false) {
+			return false;
+		}
+		if (!sem_acquire($sem)) {
+			return false;
+		}
+		return $sem;
+	}
+
+	/**
+	 * Releases the semaphore acquired from {@see Generator::guardWithSemaphore()}.
+	 *
+	 * @param resource|bool $semId the semaphore identifier returned by guardWithSemaphore
+	 * @return bool
+	 */
+	public static function unguardWithSemaphore($semId): bool {
+		if (!is_resource($semId) || !extension_loaded('sysvsem')) {
+			return false;
+		}
+		return sem_release($semId);
+	}
+
+	/**
+	 * Get the number of concurrent threads supported by the host.
+	 *
+	 * @return int number of concurrent threads, or 0 if it cannot be determined
+	 */
+	public static function getHardwareConcurrency(): int {
+		static $width;
+		if (!isset($width)) {
+			if (is_file("/proc/cpuinfo")) {
+				$width = substr_count(file_get_contents("/proc/cpuinfo"), "processor");
+			} else {
+				$width = 0;
+			}
+		}
+		return $width;
+	}
+
+	/**
+	 * Get number of concurrent preview generations from system config
+	 *
+	 * Two config entries, `preview_concurrency_new` and `preview_concurrency_all`,
+	 * are available. If not set, the default values are determined with the hardware concurrency
+	 * of the host. In case the hardware concurrency cannot be determined, or the user sets an
+	 * invalid value, fallback values are:
+	 * For new images whose previews do not exist and need to be generated, 4;
+	 * For all preview generation requests, 8.
+	 * Value of `preview_concurrency_all` should be greater than or equal to that of
+	 * `preview_concurrency_new`, otherwise, the latter is returned.
+	 *
+	 * @param string $type either `preview_concurrency_new` or `preview_concurrency_all`
+	 * @return int number of concurrent preview generations, or -1 if $type is invalid
+	 */
+	public function getNumConcurrentPreviews(string $type): int {
+		static $cached = array();
+		if (array_key_exists($type, $cached)) {
+			return $cached[$type];
+		}
+
+		$hardwareConcurrency = self::getHardwareConcurrency();
+		switch ($type) {
+			case "preview_concurrency_all":
+				$fallback = $hardwareConcurrency > 0 ? $hardwareConcurrency * 2 : 8;
+				$concurrency_all = $this->config->getSystemValueInt($type, $fallback);
+				$concurrency_new = $this->getNumConcurrentPreviews("preview_concurrency_new");
+				$cached[$type] = max($concurrency_all, $concurrency_new);
+				break;
+			case "preview_concurrency_new":
+				$fallback = $hardwareConcurrency > 0 ? $hardwareConcurrency : 4;
+				$cached[$type] = $this->config->getSystemValueInt($type, $fallback);
+				break;
+			default:
+				return -1;
+		}
+		return $cached[$type];
+	}
+
+	/**
 	 * @param ISimpleFolder $previewFolder
 	 * @param File $file
 	 * @param string $mimeType
@@ -340,7 +434,13 @@ class Generator {
 				$maxWidth = $this->config->getSystemValueInt('preview_max_x', 4096);
 				$maxHeight = $this->config->getSystemValueInt('preview_max_y', 4096);
 
-				$preview = $this->helper->getThumbnail($provider, $file, $maxWidth, $maxHeight);
+				$previewConcurrency = $this->getNumConcurrentPreviews('preview_concurrency_new');
+				$sem = self::guardWithSemaphore(self::SEMAPHORE_ID_NEW, $previewConcurrency);
+				try {
+					$preview = $this->helper->getThumbnail($provider, $file, $maxWidth, $maxHeight);
+				} finally {
+					self::unguardWithSemaphore($sem);
+				}
 
 				if (!($preview instanceof IImage)) {
 					continue;
@@ -510,29 +610,34 @@ class Generator {
 			throw new \InvalidArgumentException('Failed to generate preview, failed to load image');
 		}
 
-		if ($crop) {
-			if ($height !== $preview->height() && $width !== $preview->width()) {
-				//Resize
-				$widthR = $preview->width() / $width;
-				$heightR = $preview->height() / $height;
-
-				if ($widthR > $heightR) {
-					$scaleH = $height;
-					$scaleW = $maxWidth / $heightR;
-				} else {
-					$scaleH = $maxHeight / $widthR;
-					$scaleW = $width;
+		$previewConcurrency = $this->getNumConcurrentPreviews('preview_concurrency_new');
+		$sem = self::guardWithSemaphore(self::SEMAPHORE_ID_NEW, $previewConcurrency);
+		try {
+			if ($crop) {
+				if ($height !== $preview->height() && $width !== $preview->width()) {
+					//Resize
+					$widthR = $preview->width() / $width;
+					$heightR = $preview->height() / $height;
+
+					if ($widthR > $heightR) {
+						$scaleH = $height;
+						$scaleW = $maxWidth / $heightR;
+					} else {
+						$scaleH = $maxHeight / $widthR;
+						$scaleW = $width;
+					}
+					$preview = $preview->preciseResizeCopy((int)round($scaleW), (int)round($scaleH));
 				}
-				$preview = $preview->preciseResizeCopy((int)round($scaleW), (int)round($scaleH));
+				$cropX = (int)floor(abs($width - $preview->width()) * 0.5);
+				$cropY = (int)floor(abs($height - $preview->height()) * 0.5);
+				$preview = $preview->cropCopy($cropX, $cropY, $width, $height);
+			} else {
+				$preview = $maxPreview->resizeCopy(max($width, $height));
 			}
-			$cropX = (int)floor(abs($width - $preview->width()) * 0.5);
-			$cropY = (int)floor(abs($height - $preview->height()) * 0.5);
-			$preview = $preview->cropCopy($cropX, $cropY, $width, $height);
-		} else {
-			$preview = $maxPreview->resizeCopy(max($width, $height));
+		} finally {
+			self::unguardWithSemaphore($sem);
 		}
 
-
 		$path = $this->generatePath($width, $height, $crop, $preview->dataMimeType(), $prefix);
 		try {
 			$file = $previewFolder->newFile($path);