Don't use worker threads for repo fetching during Skyframe error bubb…

…ling

For some reason, using worker threads for repo fetching during Skyframe error bubbling frequently causes deadlocks on Linux. I wasn't able to find out why the deadlock happens, but this CL is the immediate solution to the problem, and shouldn't be a performance concern since no Skyframe restarts should happen during error bubbling anyway.

Tested on Linux; with this CL, `bazel test //src/test/shell/bazel:starlark_repository_test --test_filter=test_download_failure_message --runs_per_test=20` finishes just fine. (On an M1 macbook, I can't trigger the deadlock even without this CL.)

Fixes #21238

PiperOrigin-RevId: 606305306
Change-Id: I6f47a144b29030011f6c10c2b37f6874190fed0e

src/main/java/com/google/devtools/build/lib/bazel/repository/starlark/StarlarkRepositoryFunction.java

@@ -123,7 +123,14 @@ public RepositoryDirectoryValue.Builder fetch(
       Map<RepoRecordedInput, String> recordedInputValues,
       SkyKey key)
       throws RepositoryFunctionException, InterruptedException {
-    if (workerExecutorService == null) {
+    if (workerExecutorService == null
+        || env.inErrorBubblingForSkyFunctionsThatCanFullyRecoverFromErrors()) {
+      // Don't use the worker thread if we're in Skyframe error bubbling. For some reason, using a
+      // worker thread during error bubbling very frequently causes deadlocks on Linux platforms.
+      // The deadlock is rather elusive and this is just the immediate thing that seems to help.
+      // Fortunately, no Skyframe restarts should happen during error bubbling anyway, so this
+      // shouldn't be a performance concern. See https://github.com/bazelbuild/bazel/issues/21238
+      // for more context.
       return fetchInternal(rule, outputDirectory, directories, env, recordedInputValues, key);
     }
     var state = env.getState(RepoFetchingSkyKeyComputeState::new);

src/main/java/com/google/devtools/build/skyframe/SkyFunction.java

@@ -387,6 +387,7 @@ default void injectVersionForNonHermeticFunction(Version version) {}
      * may be called upon to transform a lower-level exception. This method can tell it whether to
      * transform a dependency's exception or ignore it and return a value as usual.
      */
+    // TODO: Rename this as it can be called for other purposes.
     boolean inErrorBubblingForSkyFunctionsThatCanFullyRecoverFromErrors();
 
     /**