EAP 7 start up slowness in ServiceModuleLoader.preloadModule

Issue

• We see slowness during start up with a large ear in org.jboss.as.server.moduleservice.ServiceModuleLoader.preloadModule calls. This was not seen previously on EAP 6:

"MSC service thread 1-8" #26 prio=5 os_prio=0 tid=0x00005635d2431800 nid=0x357c waiting for monitor entry [0x00007f1dae332000]
   java.lang.Thread.State: BLOCKED (on object monitor)
    at org.jboss.as.server.moduleservice.ServiceModuleLoader.preloadModule(ServiceModuleLoader.java:142)
    - waiting to lock <0x00000006c026f2e0> (a java.lang.Class for org.jboss.as.server.moduleservice.ServiceModuleLoader)
    at org.jboss.modules.ModuleLoader.preloadModule(ModuleLoader.java:404)
    at org.jboss.modules.Module.addExportedPaths(Module.java:1425)
    at org.jboss.modules.Module.addExportedPaths(Module.java:1473)
    at org.jboss.modules.Module.addExportedPaths(Module.java:1473)
    at org.jboss.modules.Module.addExportedPaths(Module.java:1473)
    at org.jboss.modules.Module.addExportedPaths(Module.java:1473)
    at org.jboss.modules.Module.addExportedPaths(Module.java:1473)
    at org.jboss.modules.Module.addExportedPaths(Module.java:1473)
    at org.jboss.modules.Module.addExportedPaths(Module.java:1473)
    at org.jboss.modules.Module.addExportedPaths(Module.java:1473)
    at org.jboss.modules.Module.addExportedPaths(Module.java:1473)
    at org.jboss.modules.Module.addExportedPaths(Module.java:1473)
    at org.jboss.modules.Module.addExportedPaths(Module.java:1473)
    at org.jboss.modules.Module.addExportedPaths(Module.java:1473)
    at org.jboss.modules.Module.addPaths(Module.java:1317)
    at org.jboss.modules.Module.link(Module.java:1644)
    at org.jboss.modules.Module.relink(Module.java:1688)
    at org.jboss.modules.ModuleLoader.relink(ModuleLoader.java:827)
    at org.jboss.as.server.moduleservice.ServiceModuleLoader.relinkModule(ServiceModuleLoader.java:201)
    at org.jboss.as.server.moduleservice.ModuleLoadService.start(ModuleLoadService.java:94)
    - locked <0x00000006d4a00540> (a org.jboss.as.server.moduleservice.ModuleLoadService)
    at org.jboss.msc.service.ServiceControllerImpl$StartTask.startService(ServiceControllerImpl.java:1739)
    at org.jboss.msc.service.ServiceControllerImpl$StartTask.execute(ServiceControllerImpl.java:1701)
    at org.jboss.msc.service.ServiceControllerImpl$ControllerTask.run(ServiceControllerImpl.java:1559)
    at org.jboss.threads.ContextClassLoaderSavingRunnable.run(ContextClassLoaderSavingRunnable.java:35)
    at org.jboss.threads.EnhancedQueueExecutor.safeRun(EnhancedQueueExecutor.java:1990)
    at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.doRunTask(EnhancedQueueExecutor.java:1486)
    at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.run(EnhancedQueueExecutor.java:1363)
    at java.lang.Thread.run(Thread.java:750)

"MSC service thread 1-2" #20 prio=5 os_prio=0 tid=0x00005635d1edf800 nid=0x3576 waiting for monitor entry [0x00007f1dae93b000]
   java.lang.Thread.State: BLOCKED (on object monitor)
    at org.jboss.as.server.moduleservice.ServiceModuleLoader.preloadModule(ServiceModuleLoader.java:142)
    - locked <0x00000006c026f2e0> (a java.lang.Class for org.jboss.as.server.moduleservice.ServiceModuleLoader)
    at org.jboss.modules.ModuleLoader.preloadModule(ModuleLoader.java:404)
    at org.jboss.modules.Module.addExportedPaths(Module.java:1425)
    at org.jboss.modules.Module.addExportedPaths(Module.java:1473)
    at org.jboss.modules.Module.addPaths(Module.java:1317)
    at org.jboss.modules.Module.link(Module.java:1644)
    at org.jboss.modules.Module.relink(Module.java:1688)
    at org.jboss.modules.ModuleLoader.relink(ModuleLoader.java:827)
    at org.jboss.as.server.moduleservice.ServiceModuleLoader.relinkModule(ServiceModuleLoader.java:201)
    at org.jboss.as.server.moduleservice.ModuleLoadService.start(ModuleLoadService.java:94)
    - locked <0x00000006d1915830> (a org.jboss.as.server.moduleservice.ModuleLoadService)
    at org.jboss.msc.service.ServiceControllerImpl$StartTask.startService(ServiceControllerImpl.java:1739)
    at org.jboss.msc.service.ServiceControllerImpl$StartTask.execute(ServiceControllerImpl.java:1701)
    at org.jboss.msc.service.ServiceControllerImpl$ControllerTask.run(ServiceControllerImpl.java:1559)
    at org.jboss.threads.ContextClassLoaderSavingRunnable.run(ContextClassLoaderSavingRunnable.java:35)
    at org.jboss.threads.EnhancedQueueExecutor.safeRun(EnhancedQueueExecutor.java:1990)
    at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.doRunTask(EnhancedQueueExecutor.java:1486)
    at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.run(EnhancedQueueExecutor.java:1363)
    at java.lang.Thread.run(Thread.java:750)