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8275950: Use only _thread_in_vm in ~ThreadBlockInVMPreprocess() #6120

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8275950: Use only _thread_in_vm in ~ThreadBlockInVMPreprocess() #6120

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313d242
v1
pchilano Oct 26, 2021
11da08b
remove assert in SS::block
pchilano Oct 27, 2021
068db83
fix comment in ~ThreadBlockInVMPreprocess()
pchilano Nov 1, 2021
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4 changes: 1 addition & 3 deletions src/hotspot/share/runtime/interfaceSupport.inline.hpp
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Expand Up @@ -229,14 +229,12 @@ class ThreadBlockInVMPreprocess : public ThreadStateTransition {
~ThreadBlockInVMPreprocess() {
assert(_thread->thread_state() == _thread_blocked, "coming from wrong thread state");
// Change to transition state and ensure it is seen by the VM thread.
_thread->set_thread_state_fence(_thread_blocked_trans);
_thread->set_thread_state_fence(_thread_in_vm);
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The comment on L231 is now wrong since you're no longer using
a "transition" state. Perhaps, "Change to an unsafe state..."

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Fixed.


if (SafepointMechanism::should_process(_thread, _allow_suspend)) {
_pr(_thread);
SafepointMechanism::process_if_requested(_thread, _allow_suspend);
}

_thread->set_thread_state(_thread_in_vm);
}

static void emptyOp(JavaThread* current) {}
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1 change: 0 additions & 1 deletion src/hotspot/share/runtime/safepoint.cpp
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Expand Up @@ -706,7 +706,6 @@ void SafepointSynchronize::block(JavaThread *thread) {
}

JavaThreadState state = thread->thread_state();
assert(is_a_block_safe_state(state), "Illegal threadstate encountered: %d", state);
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Getting rid of this assert makes me a bit nervous, but I have to
get used to the fact that @pchilano is making the safepointing
sub-system simpler and simpler...

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I thought about keeping it but not only we have a single caller(SafepointMechanism::process()) which already has that assert as a guarantee, but also there is no way to add new callers without basically copying all the logic from SafepointMechanism::process() since we cannot just call SS::block().

thread->frame_anchor()->make_walkable(thread);

uint64_t safepoint_id = SafepointSynchronize::safepoint_counter();
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9 changes: 1 addition & 8 deletions src/hotspot/share/runtime/safepoint.hpp
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Expand Up @@ -128,14 +128,7 @@ class SafepointSynchronize : AllStatic {

static bool is_a_block_safe_state(JavaThreadState state) {
// Check that we have a valid thread_state before blocking for safepoints
switch(state) {
case _thread_in_vm:
case _thread_in_Java: // From compiled code
case _thread_blocked_trans:
return true;
default:
return false;
}
return state == _thread_in_vm || state == _thread_in_Java;
}
// Called when a thread voluntarily blocks
static void block(JavaThread *thread);
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