Buffer blaze query

It was previously sending each label individually over gRPC, where each call
has a lot of overhead.

This makes queries with a large amount of output _a lot_ faster. For an example
query where all packages are already loaded, I observe a difference of ~3.5s
before this change to ~1.6s after this change.

PiperOrigin-RevId: 177426957

1 files changed, 10 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/query2/output/OutputFormatter.java b/src/main/java/com/google/devtools/build/lib/query2/output/OutputFormatter.java
index 7f6c173b24..d13beac249 100644
--- a/src/main/java/com/google/devtools/build/lib/query2/output/OutputFormatter.java
+++ b/src/main/java/com/google/devtools/build/lib/query2/output/OutputFormatter.java
@@ -153,6 +153,16 @@ public abstract class OutputFormatter implements Serializable {
             : DependencyFilter.NO_IMPLICIT_DEPS);
   }
 
+  /**
+   * Workaround for a bug in {@link java.nio.channels.Channels#newChannel(OutputStream)}, which
+   * attempts to close the output stream on interrupt, which can cause a deadlock if there is an
+   * ongoing write. If this formatter uses Channels.newChannel, then it must return false here, and
+   * perform its own buffering.
+   */
+  public boolean canBeBuffered() {
+    return true;
+  }
+
   public void verifyCompatible(QueryEnvironment<?> env, QueryExpression expr)
       throws QueryException {
   }