这只是一个小插曲，但是在jvm中设置线程优先级不需要调整操作系统线程的优先级吗？
linux（以及任何类似unix的操作系统）限制了将进程赋予root更高优先级的能力。我认为线程也会有类似的限制。

好吧，让我们看看来源：
第2947行：

////////////////////////////////////////////////////////////////////////////////
// thread priority support

// Note: Normal Linux applications are run with SCHED_OTHER policy. SCHED_OTHER
// only supports dynamic priority, static priority must be zero. For real-time
// applications, Linux supports SCHED_RR which allows static priority (1-99).
// However, for large multi-threaded applications, SCHED_RR is not only slower
// than SCHED_OTHER, but also very unstable (my volano tests hang hard 4 out
// of 5 runs - Sep 2005).
//
// The following code actually changes the niceness of kernel-thread/LWP. It
// has an assumption that setpriority() only modifies one kernel-thread/LWP,
// not the entire user process, and user level threads are 1:1 mapped to kernel
// threads. It has always been the case, but could change in the future. For
// this reason, the code should not be used as default (ThreadPriorityPolicy=0).
// It is only used when ThreadPriorityPolicy=1 and requires root privilege.

...
第2982行：

static int prio_init() {
   if (ThreadPriorityPolicy == 1) {
     // Only root can raise thread priority. Don't allow ThreadPriorityPolicy=1
     // if effective uid is not root. Perhaps, a more elegant way of doing
     // this is to test CAP_SYS_NICE capability, but that will require libcap.so
     if (geteuid() != 0) {
       if (!FLAG_IS_DEFAULT(ThreadPriorityPolicy)) {
         warning("-XX:ThreadPriorityPolicy requires root privilege on Linux");
       }
       ThreadPriorityPolicy = 0;
     }
   }
   return 0;
 }

...
第2997行：

OSReturn os::set_native_priority(Thread* thread, int newpri) {
  if ( !UseThreadPriorities || ThreadPriorityPolicy == 0 ) return OS_OK;

  int ret = setpriority(PRIO_PROCESS, thread->osthread()->thread_id(), newpri);
  return (ret == 0) ? OS_OK : OS_ERR;
}

所以！至少在sunjava上，在linux上，你不会看到线程优先级，除非你已经做了 -XX:ThreadPriorityPolicy 这似乎需要根。

默认的linux线程调度程序策略sched\u other不支持优先级。或者更确切地说，它支持一个值为0的优先级设置。其他所谓的“实时”策略sched\u fifo和sched\u rr支持更高的优先级，但仅对具有超级用户权限的进程可用。