8221207: Redo JDK-8218446 - SuspendAtExit hangs

Reviewed-by: rehn, dcubed
This commit is contained in:
David Holmes 2019-03-25 00:57:03 -04:00
parent 5793068c77
commit ccef9efb14
2 changed files with 47 additions and 61 deletions

View File

@ -2264,48 +2264,19 @@ void JavaThread::check_and_handle_async_exceptions(bool check_unsafe_error) {
void JavaThread::handle_special_runtime_exit_condition(bool check_asyncs) {
//
// Check for pending external suspend. Internal suspend requests do
// not use handle_special_runtime_exit_condition().
// Check for pending external suspend.
// If JNIEnv proxies are allowed, don't self-suspend if the target
// thread is not the current thread. In older versions of jdbx, jdbx
// threads could call into the VM with another thread's JNIEnv so we
// can be here operating on behalf of a suspended thread (4432884).
bool do_self_suspend = is_external_suspend_with_lock();
if (do_self_suspend && (!AllowJNIEnvProxy || this == JavaThread::current())) {
//
// Because thread is external suspended the safepoint code will count
// thread as at a safepoint. This can be odd because we can be here
// as _thread_in_Java which would normally transition to _thread_blocked
// at a safepoint. We would like to mark the thread as _thread_blocked
// before calling java_suspend_self like all other callers of it but
// we must then observe proper safepoint protocol. (We can't leave
// _thread_blocked with a safepoint in progress). However we can be
// here as _thread_in_native_trans so we can't use a normal transition
// constructor/destructor pair because they assert on that type of
// transition. We could do something like:
//
// JavaThreadState state = thread_state();
// set_thread_state(_thread_in_vm);
// {
// ThreadBlockInVM tbivm(this);
// java_suspend_self()
// }
// set_thread_state(_thread_in_vm_trans);
// if (safepoint) block;
// set_thread_state(state);
//
// but that is pretty messy. Instead we just go with the way the
// code has worked before and note that this is the only path to
// java_suspend_self that doesn't put the thread in _thread_blocked
// mode.
frame_anchor()->make_walkable(this);
java_suspend_self();
// We might be here for reasons in addition to the self-suspend request
// so check for other async requests.
java_suspend_self_with_safepoint_check();
}
// We might be here for reasons in addition to the self-suspend request
// so check for other async requests.
if (check_asyncs) {
check_and_handle_async_exceptions();
}
@ -2424,6 +2395,7 @@ void JavaThread::java_suspend() {
// to complete an external suspend request.
//
int JavaThread::java_suspend_self() {
assert(thread_state() == _thread_blocked, "wrong state for java_suspend_self()");
int ret = 0;
// we are in the process of exiting so don't suspend
@ -2471,6 +2443,36 @@ int JavaThread::java_suspend_self() {
return ret;
}
// Helper routine to set up the correct thread state before calling java_suspend_self.
// This is called when regular thread-state transition helpers can't be used because
// we can be in various states, in particular _thread_in_native_trans.
// Because this thread is external suspended the safepoint code will count it as at
// a safepoint, regardless of what its actual current thread-state is. But
// is_ext_suspend_completed() may be waiting to see a thread transition from
// _thread_in_native_trans to _thread_blocked. So we set the thread state directly
// to _thread_blocked. The problem with setting thread state directly is that a
// safepoint could happen just after java_suspend_self() returns after being resumed,
// and the VM thread will see the _thread_blocked state. So we must check for a safepoint
// after restoring the state to make sure we won't leave while a safepoint is in progress.
// However, not all initial-states are allowed when performing a safepoint check, as we
// should never be blocking at a safepoint whilst in those states. Of these 'bad' states
// only _thread_in_native is possible when executing this code (based on our two callers).
// A thread that is _thread_in_native is already safepoint-safe and so it doesn't matter
// whether the VMThread sees the _thread_blocked state, or the _thread_in_native state,
// and so we don't need the explicit safepoint check.
void JavaThread::java_suspend_self_with_safepoint_check() {
assert(this == Thread::current(), "invariant");
JavaThreadState state = thread_state();
set_thread_state(_thread_blocked);
java_suspend_self();
set_thread_state(state);
InterfaceSupport::serialize_thread_state_with_handler(this);
if (state != _thread_in_native) {
SafepointMechanism::block_if_requested(this);
}
}
#ifdef ASSERT
// Verify the JavaThread has not yet been published in the Threads::list, and
// hence doesn't need protection from concurrent access at this stage.
@ -2502,33 +2504,11 @@ void JavaThread::check_safepoint_and_suspend_for_native_trans(JavaThread *thread
// threads could call into the VM with another thread's JNIEnv so we
// can be here operating on behalf of a suspended thread (4432884).
if (do_self_suspend && (!AllowJNIEnvProxy || curJT == thread)) {
JavaThreadState state = thread->thread_state();
// We mark this thread_blocked state as a suspend-equivalent so
// that a caller to is_ext_suspend_completed() won't be confused.
// The suspend-equivalent state is cleared by java_suspend_self().
thread->set_suspend_equivalent();
// If the safepoint code sees the _thread_in_native_trans state, it will
// wait until the thread changes to other thread state. There is no
// guarantee on how soon we can obtain the SR_lock and complete the
// self-suspend request. It would be a bad idea to let safepoint wait for
// too long. Temporarily change the state to _thread_blocked to
// let the VM thread know that this thread is ready for GC. The problem
// of changing thread state is that safepoint could happen just after
// java_suspend_self() returns after being resumed, and VM thread will
// see the _thread_blocked state. We must check for safepoint
// after restoring the state and make sure we won't leave while a safepoint
// is in progress.
thread->set_thread_state(_thread_blocked);
thread->java_suspend_self();
thread->set_thread_state(state);
InterfaceSupport::serialize_thread_state_with_handler(thread);
thread->java_suspend_self_with_safepoint_check();
} else {
SafepointMechanism::block_if_requested(curJT);
}
SafepointMechanism::block_if_requested(curJT);
if (thread->is_deopt_suspend()) {
thread->clear_deopt_suspend();
RegisterMap map(thread, false);

View File

@ -1348,10 +1348,16 @@ class JavaThread: public Thread {
inline void clear_ext_suspended();
public:
void java_suspend();
void java_resume();
int java_suspend_self();
void java_suspend(); // higher-level suspension logic called by the public APIs
void java_resume(); // higher-level resume logic called by the public APIs
int java_suspend_self(); // low-level self-suspension mechanics
private:
// mid-level wrapper around java_suspend_self to set up correct state and
// check for a pending safepoint at the end
void java_suspend_self_with_safepoint_check();
public:
void check_and_wait_while_suspended() {
assert(JavaThread::current() == this, "sanity check");