Add test

Author: fmeum

src/test/java/com/google/devtools/build/lib/remote/disk/BUILD

@@ -30,6 +30,7 @@ java_test(
         "//src/test/java/com/google/devtools/build/lib:test_runner",
         "//src/test/java/com/google/devtools/build/lib/testutil:TestUtils",
         "//src/test/java/com/google/devtools/build/lib/testutil:external_file_system_lock",
+        "//src/test/java/com/google/devtools/build/lib/vfs/util:util_internal",
         "//third_party:error_prone_annotations",
         "//third_party:guava",
         "//third_party:junit4",

src/test/java/com/google/devtools/build/lib/remote/disk/DiskCacheClientTest.java

@@ -33,19 +33,24 @@
 import com.google.devtools.build.lib.remote.common.OutputDigestMismatchException;
 import com.google.devtools.build.lib.remote.common.RemoteCacheClient.ActionKey;
 import com.google.devtools.build.lib.remote.util.DigestUtil;
+import com.google.devtools.build.lib.testutil.TestUtils;
 import com.google.devtools.build.lib.vfs.DigestHashFunction;
 import com.google.devtools.build.lib.vfs.FileSystem;
 import com.google.devtools.build.lib.vfs.FileSystemUtils;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.lib.vfs.SyscallCache;
 import com.google.devtools.build.lib.vfs.bazel.BazelHashFunctions;
 import com.google.devtools.build.lib.vfs.inmemoryfs.InMemoryFileSystem;
+import com.google.devtools.build.lib.vfs.util.FileSystems;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.protobuf.ByteString;
 import com.google.protobuf.Message;
 import java.io.IOException;
+import java.util.ArrayList;
+import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -347,6 +352,44 @@ public void downloadActionResult_withReferencedTreeFileMissing_returnsNull() thr
     assertThat(result).isNull();
   }
 
+  @Test
+  public void concurrentUploadDownload()
+      throws IOException, ExecutionException, InterruptedException {
+    var nativeDiskCacheDir = TestUtils.createUniqueTmpDir(FileSystems.getNativeFileSystem());
+    try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
+      var nativeClient =
+          new DiskCacheClient(
+              nativeDiskCacheDir, DIGEST_UTIL, executor, /* verifyDownloads= */ false);
+      var tasks = new ArrayList<Future<?>>();
+      for (int attempt = 0; attempt < 100; attempt++) {
+        var contentString = "file contents " + attempt;
+        var contentBytes = ByteString.copyFromUtf8(contentString);
+        var contentDigest = getDigest(contentString);
+        // Start multiple concurrent upload/download tasks in an attempt to exercise the
+        // interleaving in which both multiple uploadBlob calls initially see the entry as missing
+        // and thus try to create it.
+        for (int concurrentOp = 0; concurrentOp < 5; concurrentOp++) {
+          tasks.add(
+              executor.submit(
+                  () -> {
+                    nativeClient.uploadBlob(contentDigest, contentBytes);
+                    try (var out = ByteString.newOutput()) {
+                      getFromFuture(nativeClient.downloadBlob(contentDigest, out));
+                      var downloadedBytes = out.toByteString();
+                      assertThat(downloadedBytes).isEqualTo(contentBytes);
+                    } catch (CacheNotFoundException ignored) {
+                      // This task won the race over the upload task.
+                    }
+                    return null;
+                  }));
+        }
+      }
+      for (var task : tasks) {
+        task.get();
+      }
+    }
+  }
+
   private Tree getTreeWithFile(Digest fileDigest) {
     return Tree.newBuilder()
         .addChildren(Directory.newBuilder().addFiles(FileNode.newBuilder().setDigest(fileDigest)))