Index executors: Use directExecutor for negative thread values

This will make it easier to test index-related logic in tests. We still
use 0 as a default way of setting the JVM threads.

Change-Id: If186a23ee4e79c49306bf9f286a24841d99e6531

Documentation/config-gerrit.txt

@@ -2779,16 +2779,16 @@ Number of threads to use for indexing in normal interactive operations. Setting
 it to 0 disables the dedicated thread pool and indexing will be done in the same
 thread as the operation.
 +
-If not set or set to a negative value, defaults to 1 plus half of the number of
-logical CPUs as returned by the JVM.
+If not set or set to a zero, defaults to the number of logical CPUs as returned
+by the JVM. If set to a negative value, defaults to a direct executor.
 
 [[index.batchThreads]]index.batchThreads::
 +
 Number of threads to use for indexing in background operations, such as
 online schema upgrades.
 +
-If not set or set to a negative value, defaults to the number of logical
-CPUs as returned by the JVM.
+If not set or set to a zero, defaults to the number of logical CPUs as returned
+by the JVM. If set to a negative value, defaults to a direct executor.
 
 [[index.onlineUpgrade]]index.onlineUpgrade::
 +

java/com/google/gerrit/acceptance/AbstractDaemonTest.java

@@ -397,6 +397,8 @@ public abstract class AbstractDaemonTest {
       baseConfig.setString("sshd", null, "listenAddress", "off");
     }
 
+    baseConfig.setInt("index", null, "batchThreads", -1);
+
     baseConfig.setInt("receive", null, "changeUpdateThreads", 4);
     Module module = createModule();
     if (classDesc.equals(methodDesc) && !classDesc.sandboxed() && !methodDesc.sandboxed()) {

java/com/google/gerrit/server/index/IndexModule.java

@@ -104,7 +104,7 @@ public class IndexModule extends LifecycleModule {
 
   public IndexModule(
       ListeningExecutorService interactiveExecutor, ListeningExecutorService batchExecutor) {
-    this.threads = -1;
+    this.threads = 0;
     this.interactiveExecutor = interactiveExecutor;
     this.batchExecutor = batchExecutor;
     this.closeExecutorsOnShutdown = false;
@@ -211,11 +211,12 @@ public class IndexModule extends LifecycleModule {
       return interactiveExecutor;
     }
     int threads = this.threads;
-    if (threads <= 0) {
-      threads = config.getInt("index", null, "threads", 0);
-    }
-    if (threads <= 0) {
-      threads = Runtime.getRuntime().availableProcessors() / 2 + 1;
+    if (threads < 0) {
+      return MoreExecutors.newDirectExecutorService();
+    } else if (threads == 0) {
+      threads =
+          config.getInt(
+              "index", null, "threads", Runtime.getRuntime().availableProcessors() / 2 + 1);
     }
     return MoreExecutors.listeningDecorator(
         workQueue.createQueue(threads, "Index-Interactive", true));
@@ -230,7 +231,9 @@ public class IndexModule extends LifecycleModule {
       return batchExecutor;
     }
     int threads = config.getInt("index", null, "batchThreads", 0);
-    if (threads <= 0) {
+    if (threads < 0) {
+      return MoreExecutors.newDirectExecutorService();
+    } else if (threads == 0) {
       threads = Runtime.getRuntime().availableProcessors();
     }
     return MoreExecutors.listeningDecorator(workQueue.createQueue(threads, "Index-Batch", true));