kill -3dumpStackTraces

最近在看一个watchdog问题，是由于线程D状态引起的，但是没有打印出native/kernel的调用栈，不知道这个线程导致block在哪里了，不太好分析问题，调用栈如下：

"Binder:1176_17" prio=5 tid=120 Native
  | group="main" sCount=1 dsCount=0 obj=0x140c3100 self=0x7f74a52a00
  | sysTid=2774 nice=0 cgrp=default sched=0/0 handle=0x7f71f00440
  | state=D schedstat=( 71108648427 27941348162 142494 ) utm=4190 stm=2920 core=4 HZ=100
  | stack=0x7f71e04000-0x7f71e06000 stackSize=1013KB
  | held mutexes=
  at com.android.server.power.PowerManagerService.nativeReleaseSuspendBlocker(Native method)
  at com.android.server.power.PowerManagerService.access$3900(PowerManagerService.java:101)
  at com.android.server.power.PowerManagerService$SuspendBlockerImpl.release(PowerManagerService.java:3523)
  - locked <0x01889afd> (a com.android.server.power.PowerManagerService$SuspendBlockerImpl)
  at com.android.server.power.PowerManagerService.updateSuspendBlockerLocked(PowerManagerService.java:2570)
  at com.android.server.power.PowerManagerService.updatePowerStateLocked(PowerManagerService.java:1643)
  at com.android.server.power.PowerManagerService.removeWakeLockLocked(PowerManagerService.java:1106)
  at com.android.server.power.PowerManagerService.releaseWakeLockInternal(PowerManagerService.java:1080)
  - locked <0x09ee3aa7> (a java.lang.Object)
  at com.android.server.power.PowerManagerService.access$4400(PowerManagerService.java:101)
  at com.android.server.power.PowerManagerService$BinderService.releaseWakeLock(PowerManagerService.java:3604)
  at android.os.IPowerManager$Stub.onTransact(IPowerManager.java:94)
  at android.os.Binder.execTransact(Binder.java:460)

所以花时间调查一个dumpStackTraces没有打印出kernel和native调用栈的问题，大概看了一下调用流程：

void Thread::Dump(std::ostream& os, BacktraceMap* backtrace_map) const {
  DumpState(os);
  DumpStack(os, backtrace_map);
}

继续看看DumpStack方法：

void Thread::DumpStack(std::ostream& os, BacktraceMap* backtrace_map) const {
  // TODO: we call this code when dying but may not have suspended the thread ourself. The
  //       IsSuspended check is therefore racy with the use for dumping (normally we inhibit
  //       the race with the thread_suspend_count_lock_).
  bool dump_for_abort = (gAborting > 0);
  bool safe_to_dump = (this == Thread::Current() || IsSuspended());
  if (!kIsDebugBuild) {
    // We always want to dump the stack for an abort, however, there is no point dumping another
    // thread's stack in debug builds where we'll hit the not suspended check in the stack walk.
    safe_to_dump = (safe_to_dump || dump_for_abort);
  }
  if (safe_to_dump) {
    // If we're currently in native code, dump that stack before dumping the managed stack.
    if (dump_for_abort || ShouldShowNativeStack(this)) {
      DumpKernelStack(os, GetTid(), "  kernel: ", false);
      ArtMethod* method = GetCurrentMethod(nullptr, !dump_for_abort);
      DumpNativeStack(os, GetTid(), backtrace_map, "  native: ", method);
    }
    DumpJavaStack(os);
  } else {
    os << "Not able to dump stack of thread that isn't suspended";
  }
}

这里会调用DumpKernelStack/DumpNativeStack/DumpJavaStack/方法，但是在调用前有一个判断：ShouldShowNativeStack

static bool ShouldShowNativeStack(const Thread* thread)
    SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
  ThreadState state = thread->GetState();

  #ifdef MTK_ART_DONT_DUMP_NATIVE_STACK_FOR_LARGE_PROCESS
  if ((thread->GetThreadId()) < 8 || (thread->GetThreadId() > 20)) {
    return false;
  }
  #endif

  // In native code somewhere in the VM (one of the kWaitingFor* states)? That's interesting.
  if (state > kWaiting && state < kStarting) {
    return true;
  }

  // In an Object.wait variant or Thread.sleep? That's not interesting.
  if (state == kTimedWaiting || state == kSleeping || state == kWaiting) {
    return false;
  }

  // Threads with no managed stack frames should be shown.
  const ManagedStack* managed_stack = thread->GetManagedStack();
  if (managed_stack == nullptr || (managed_stack->GetTopQuickFrame() == nullptr &&
      managed_stack->GetTopShadowFrame() == nullptr)) {
    return true;
  }

  // In some other native method? That's interesting.
  // We don't just check kNative because native methods will be in state kSuspended if they're
  // calling back into the VM, or kBlocked if they're blocked on a monitor, or one of the
  // thread-startup states if it's early enough in their life cycle (http://b/7432159).
  ArtMethod* current_method = thread->GetCurrentMethod(nullptr);
  return current_method != nullptr && current_method->IsNative();
}

上边这里进行了一系列的判断，里边有一个mtk加的代码，线程号小于8大于20就返回false.....对比了一下traces.txt文件，确实是只打印了8-20号线程的调用栈。。。。。‘

  #ifdef MTK_ART_DONT_DUMP_NATIVE_STACK_FOR_LARGE_PROCESS
  if ((thread->GetThreadId()) < 8 || (thread->GetThreadId() > 20)) {
    return false;
  }
  #endif