Make it possible to avoid an extra stat() when obtaining a digest fro…

…m the cache.

For now, it's only used to optimize out a stat() required by the execution log, which adds up for very large tree artifacts. However, there are other callsites that could be refactored to benefit from it.

PiperOrigin-RevId: 606891771
Change-Id: Ib2f6428009b86e609f4e46c4ac0ac4b2714414ff

src/main/java/com/google/devtools/build/lib/exec/SpawnLogContext.java

@@ -38,6 +38,7 @@
 import com.google.devtools.build.lib.remote.options.RemoteOptions;
 import com.google.devtools.build.lib.vfs.DigestHashFunction;
 import com.google.devtools.build.lib.vfs.DigestUtils;
+import com.google.devtools.build.lib.vfs.FileStatus;
 import com.google.devtools.build.lib.vfs.FileSystem;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.lib.vfs.PathFragment;
@@ -172,14 +173,13 @@ protected Digest computeDigest(
       }
     }
 
-    long fileSize = path.getFileSize();
-
-    // Try to obtain a digest from the filesystem.
+    // Obtain a digest from the filesystem.
+    FileStatus status = path.stat();
     return builder
         .setHash(
-            HashCode.fromBytes(DigestUtils.getDigestWithManualFallback(path, xattrProvider))
+            HashCode.fromBytes(DigestUtils.getDigestWithManualFallback(path, xattrProvider, status))
                 .toString())
-        .setSizeBytes(fileSize)
+        .setSizeBytes(status.getSize())
         .build();
   }
 

src/main/java/com/google/devtools/build/lib/vfs/DigestUtils.java

@@ -19,6 +19,7 @@
 import com.google.common.base.Preconditions;
 import com.google.common.primitives.Longs;
 import java.io.IOException;
+import javax.annotation.Nullable;
 
 /**
  * Utility class for getting digests of files.
@@ -159,27 +160,57 @@ public static CacheStats getCacheStats() {
    * <p>If {@link Path#getFastDigest} has already been attempted and was not available, call {@link
    * #manuallyComputeDigest} to skip an additional attempt to obtain the fast digest.
    *
-   * @param path Path of the file.
+   * <p>Prefer calling {@link #manuallyComputeDigest(Path, FileStatus)} when a recently obtained
+   * {@link FileStatus} is available.
+   *
+   * @param path the file path
    */
   public static byte[] getDigestWithManualFallback(Path path, XattrProvider xattrProvider)
       throws IOException {
+    return getDigestWithManualFallback(path, xattrProvider, null);
+  }
+
+  /**
+   * Same as {@link #getDigestWithManualFallback(Path, XattrProvider)}, but providing the ability to
+   * reuse a recently obtained {@link FileStatus}.
+   *
+   * @param path the file path
+   * @param status a recently obtained file status, if available
+   */
+  public static byte[] getDigestWithManualFallback(
+      Path path, XattrProvider xattrProvider, @Nullable FileStatus status) throws IOException {
     byte[] digest = xattrProvider.getFastDigest(path);
-    return digest != null ? digest : manuallyComputeDigest(path);
+    return digest != null ? digest : manuallyComputeDigest(path, status);
   }
 
   /**
-   * Calculates the digest manually.
+   * Calculates a digest manually (i.e., assuming that a fast digest can't obtained).
+   *
+   * <p>Prefer calling {@link #manuallyComputeDigest(Path, FileStatus)} when a recently obtained
+   * {@link FileStatus} is available.
    *
-   * @param path Path of the file.
+   * @param path the file path
    */
   public static byte[] manuallyComputeDigest(Path path) throws IOException {
+    return manuallyComputeDigest(path, null);
+  }
+
+  /**
+   * Same as {@link #manuallyComputeDigest(Path)}, but providing the ability to reuse a recently
+   * obtained {@link FileStatus}.
+   *
+   * @param path the file path
+   * @param status a recently obtained file status, if available
+   */
+  public static byte[] manuallyComputeDigest(Path path, @Nullable FileStatus status)
+      throws IOException {
     byte[] digest;
 
     // Attempt a cache lookup if the cache is enabled.
     Cache<CacheKey, byte[]> cache = globalCache;
     CacheKey key = null;
     if (cache != null) {
-      key = new CacheKey(path, path.stat());
+      key = new CacheKey(path, status != null ? status : path.stat());
       digest = cache.getIfPresent(key);
       if (digest != null) {
         return digest;