pass FJP a fake thread factory to diagnose cases of too early FJP initialization

platform/boot/src/com/intellij/concurrency/IdeaForkJoinWorkerThreadFactory.java

@@ -37,6 +37,13 @@ public class IdeaForkJoinWorkerThreadFactory implements ForkJoinPool.ForkJoinWor
     }
   }
 
+  public static void setupPoisonFactory() {
+    // if this method is called early enough and app called setupForkJoinCommonPool() too late
+    // (setupForkJoinCommonPool() has to be called after Main.setFlags() but before FJP init)
+    // then on the first use the FJP will explode, revealing who did the too early FJP init
+    System.setProperty("java.util.concurrent.ForkJoinPool.common.threadFactory", PoisonFactory.class.getName());
+  }
+
   private static final AtomicLong bits = new AtomicLong();
   @Override
   public ForkJoinWorkerThread newThread(ForkJoinPool pool) {

platform/boot/src/com/intellij/concurrency/PoisonFactory.java

@@ -0,0 +1,19 @@
+// Copyright 2000-2017 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+package com.intellij.concurrency;
+
+import java.util.concurrent.ForkJoinPool;
+import java.util.concurrent.ForkJoinWorkerThread;
+
+public class PoisonFactory implements ForkJoinPool.ForkJoinWorkerThreadFactory{
+  public PoisonFactory() {
+    RuntimeException exception = new RuntimeException("ForkJoinPool initialized too early, IdeaForkJoinWorkerThreadFactory ignored");
+    exception.printStackTrace();
+    exception.printStackTrace(System.out);
+    throw exception;
+  }
+
+  @Override
+  public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
+    throw new RuntimeException();
+  }
+}

platform/platform-impl/src/com/intellij/idea/StartupUtil.java

@@ -1,6 +1,7 @@
 // Copyright 2000-2017 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.intellij.idea;
 
+import com.intellij.concurrency.IdeaForkJoinWorkerThreadFactory;
 import com.intellij.ide.cloudConfig.CloudConfigProvider;
 import com.intellij.ide.customize.CustomizeIDEWizardDialog;
 import com.intellij.ide.customize.CustomizeIDEWizardStepsProvider;
@@ -74,6 +75,7 @@ public class StartupUtil {
   }
 
   static void prepareAndStart(String[] args, AppStarter appStarter) {
+    IdeaForkJoinWorkerThreadFactory.setupPoisonFactory();
     boolean newConfigFolder = false;
 
     if (!Main.isHeadless()) {

platform/testFramework/src/com/intellij/testFramework/UsefulTestCase.java

@@ -87,6 +87,7 @@ public abstract class UsefulTestCase extends TestCase {
   private static final Map<String, Long> TOTAL_TEARDOWN_COST_MILLIS = new HashMap<>();
 
   static {
+    IdeaForkJoinWorkerThreadFactory.setupPoisonFactory();
     Logger.setFactory(TestLoggerFactory.class);
   }
   protected static final Logger LOG = Logger.getInstance(UsefulTestCase.class);

platform/testFramework/src/com/intellij/testFramework/fixtures/impl/BaseFixture.java

@@ -15,6 +15,7 @@
  */
 package com.intellij.testFramework.fixtures.impl;
 
+import com.intellij.concurrency.IdeaForkJoinWorkerThreadFactory;
 import com.intellij.openapi.Disposable;
 import com.intellij.openapi.util.Disposer;
 import com.intellij.testFramework.EdtTestUtil;
@@ -31,6 +32,10 @@ public class BaseFixture implements IdeaTestFixture {
   private boolean myDisposed;
   private final Disposable myTestRootDisposable = Disposer.newDisposable();
 
+  static {
+    IdeaForkJoinWorkerThreadFactory.setupPoisonFactory();
+  }
+
   @Override
   public void setUp() throws Exception {
     Assert.assertFalse("setUp() already has been called", myInitialized);