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/*
* Copyright (c) 2017, 2022, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/
#include "precompiled.hpp"
#include "classfile/javaClasses.hpp"
#include "classfile/vmSymbols.hpp"
#include "jvm_io.h"
#include "logging/log.hpp"
#include "logging/logStream.hpp"
#include "memory/resourceArea.hpp"
#include "runtime/atomic.hpp"
#include "runtime/globals.hpp"
#include "runtime/handshake.hpp"
#include "runtime/interfaceSupport.inline.hpp"
#include "runtime/javaThread.inline.hpp"
#include "runtime/os.hpp"
#include "runtime/osThread.hpp"
#include "runtime/stackWatermarkSet.hpp"
#include "runtime/task.hpp"
#include "runtime/threadSMR.hpp"
#include "runtime/vmThread.hpp"
#include "utilities/formatBuffer.hpp"
#include "utilities/filterQueue.inline.hpp"
#include "utilities/globalDefinitions.hpp"
#include "utilities/preserveException.hpp"
#include "utilities/systemMemoryBarrier.hpp"
class HandshakeOperation : public CHeapObj<mtThread> {
friend class HandshakeState;
protected:
HandshakeClosure* _handshake_cl;
// Keeps track of emitted and completed handshake operations.
// Once it reaches zero all handshake operations have been performed.
int32_t _pending_threads;
JavaThread* _target;
Thread* _requester;
// Must use AsyncHandshakeOperation when using AsyncHandshakeClosure.
HandshakeOperation(AsyncHandshakeClosure* cl, JavaThread* target, Thread* requester) :
_handshake_cl(cl),
_pending_threads(1),
_target(target),
_requester(requester) {}
public:
HandshakeOperation(HandshakeClosure* cl, JavaThread* target, Thread* requester) :
_handshake_cl(cl),
_pending_threads(1),
_target(target),
_requester(requester) {}
virtual ~HandshakeOperation() {}
void prepare(JavaThread* current_target, Thread* executing_thread);
void do_handshake(JavaThread* thread);
bool is_completed() {
int32_t val = Atomic::load(&_pending_threads);
assert(val >= 0, "_pending_threads=%d cannot be negative", val);
return val == 0;
}
void add_target_count(int count) { Atomic::add(&_pending_threads, count); }
int32_t pending_threads() { return Atomic::load(&_pending_threads); }
const char* name() { return _handshake_cl->name(); }
bool is_async() { return _handshake_cl->is_async(); }
bool is_suspend() { return _handshake_cl->is_suspend(); }
bool is_async_exception() { return _handshake_cl->is_async_exception(); }
};
class AsyncHandshakeOperation : public HandshakeOperation {
private:
jlong _start_time_ns;
public:
AsyncHandshakeOperation(AsyncHandshakeClosure* cl, JavaThread* target, jlong start_ns)
: HandshakeOperation(cl, target, NULL), _start_time_ns(start_ns) {}
virtual ~AsyncHandshakeOperation() { delete _handshake_cl; }
jlong start_time() const { return _start_time_ns; }
};
// Performing handshakes requires a custom yielding strategy because without it
// there is a clear performance regression vs plain spinning. We keep track of
// when we last saw progress by looking at why each targeted thread has not yet
// completed its handshake. After spinning for a while with no progress we will
// yield, but as long as there is progress, we keep spinning. Thus we avoid
// yielding when there is potential work to be done or the handshake is close
// to being finished.
class HandshakeSpinYield : public StackObj {
private:
jlong _start_time_ns;
jlong _last_spin_start_ns;
jlong _spin_time_ns;
int _result_count[2][HandshakeState::_number_states];
int _prev_result_pos;
int current_result_pos() { return (_prev_result_pos + 1) & 0x1; }
void wait_raw(jlong now) {
// We start with fine-grained nanosleeping until a millisecond has
// passed, at which point we resort to plain naked_short_sleep.
if (now - _start_time_ns < NANOSECS_PER_MILLISEC) {
os::naked_short_nanosleep(10 * (NANOUNITS / MICROUNITS));
} else {
os::naked_short_sleep(1);
}
}
void wait_blocked(JavaThread* self, jlong now) {
ThreadBlockInVM tbivm(self);
wait_raw(now);
}
bool state_changed() {
for (int i = 0; i < HandshakeState::_number_states; i++) {
if (_result_count[0][i] != _result_count[1][i]) {
return true;
}
}
return false;
}
void reset_state() {
_prev_result_pos++;
for (int i = 0; i < HandshakeState::_number_states; i++) {
_result_count[current_result_pos()][i] = 0;
}
}
public:
HandshakeSpinYield(jlong start_time) :
_start_time_ns(start_time), _last_spin_start_ns(start_time),
_spin_time_ns(0), _result_count(), _prev_result_pos(0) {
const jlong max_spin_time_ns = 100 /* us */ * (NANOUNITS / MICROUNITS);
int free_cpus = os::active_processor_count() - 1;
_spin_time_ns = (5 /* us */ * (NANOUNITS / MICROUNITS)) * free_cpus; // zero on UP
_spin_time_ns = _spin_time_ns > max_spin_time_ns ? max_spin_time_ns : _spin_time_ns;
}
void add_result(HandshakeState::ProcessResult pr) {
_result_count[current_result_pos()][pr]++;
}
void process() {
jlong now = os::javaTimeNanos();
if (state_changed()) {
reset_state();
// We spin for x amount of time since last state change.
_last_spin_start_ns = now;
return;
}
jlong wait_target = _last_spin_start_ns + _spin_time_ns;
if (wait_target < now) {
// On UP this is always true.
Thread* self = Thread::current();
if (self->is_Java_thread()) {
wait_blocked(JavaThread::cast(self), now);
} else {
wait_raw(now);
}
_last_spin_start_ns = os::javaTimeNanos();
}
reset_state();
}
};
static void handle_timeout(HandshakeOperation* op, JavaThread* target) {
JavaThreadIteratorWithHandle jtiwh;
log_error(handshake)("Handshake timeout: %s(" INTPTR_FORMAT "), pending threads: " INT32_FORMAT,
op->name(), p2i(op), op->pending_threads());
if (target == NULL) {
for ( ; JavaThread* thr = jtiwh.next(); ) {
if (thr->handshake_state()->operation_pending(op)) {
log_error(handshake)("JavaThread " INTPTR_FORMAT " has not cleared handshake op: " INTPTR_FORMAT, p2i(thr), p2i(op));
// Remember the last one found for more diagnostics below.
target = thr;
}
}
} else {
log_error(handshake)("JavaThread " INTPTR_FORMAT " has not cleared handshake op: " INTPTR_FORMAT, p2i(target), p2i(op));
}
if (target != NULL) {
if (os::signal_thread(target, SIGILL, "cannot be handshaked")) {
// Give target a chance to report the error and terminate the VM.
os::naked_sleep(3000);
}
} else {
log_error(handshake)("No thread with an unfinished handshake op(" INTPTR_FORMAT ") found.", p2i(op));
}
fatal("Handshake timeout");
}
static void check_handshake_timeout(jlong start_time, HandshakeOperation* op, JavaThread* target = NULL) {
// Check if handshake operation has timed out
jlong timeout_ns = millis_to_nanos(HandshakeTimeout);
if (timeout_ns > 0) {
if (os::javaTimeNanos() >= (start_time + timeout_ns)) {
handle_timeout(op, target);
}
}
}
static void log_handshake_info(jlong start_time_ns, const char* name, int targets, int emitted_handshakes_executed, const char* extra = NULL) {
if (log_is_enabled(Info, handshake)) {
jlong completion_time = os::javaTimeNanos() - start_time_ns;
log_info(handshake)("Handshake \"%s\", Targeted threads: %d, Executed by requesting thread: %d, Total completion time: " JLONG_FORMAT " ns%s%s",
name, targets,
emitted_handshakes_executed,
completion_time,
extra != NULL ? ", " : "",
extra != NULL ? extra : "");
}
}
class VM_HandshakeAllThreads: public VM_Operation {
HandshakeOperation* const _op;
public:
VM_HandshakeAllThreads(HandshakeOperation* op) : _op(op) {}
bool evaluate_at_safepoint() const { return false; }
void doit() {
jlong start_time_ns = os::javaTimeNanos();
JavaThreadIteratorWithHandle jtiwh;
int number_of_threads_issued = 0;
for (JavaThread* thr = jtiwh.next(); thr != NULL; thr = jtiwh.next()) {
thr->handshake_state()->add_operation(_op);
number_of_threads_issued++;
}
if (UseSystemMemoryBarrier) {
SystemMemoryBarrier::emit();
}
if (number_of_threads_issued < 1) {
log_handshake_info(start_time_ns, _op->name(), 0, 0, "no threads alive");
return;
}
// _op was created with a count == 1 so don't double count.
_op->add_target_count(number_of_threads_issued - 1);
log_trace(handshake)("Threads signaled, begin processing blocked threads by VMThread");
HandshakeSpinYield hsy(start_time_ns);
// Keeps count on how many of own emitted handshakes
// this thread execute.
int emitted_handshakes_executed = 0;
do {
// Check if handshake operation has timed out
check_handshake_timeout(start_time_ns, _op);
// Have VM thread perform the handshake operation for blocked threads.
// Observing a blocked state may of course be transient but the processing is guarded
// by mutexes and we optimistically begin by working on the blocked threads
jtiwh.rewind();
for (JavaThread* thr = jtiwh.next(); thr != NULL; thr = jtiwh.next()) {
// A new thread on the ThreadsList will not have an operation,
// hence it is skipped in handshake_try_process.
HandshakeState::ProcessResult pr = thr->handshake_state()->try_process(_op);
hsy.add_result(pr);
if (pr == HandshakeState::_succeeded) {
emitted_handshakes_executed++;
}
}
hsy.process();
} while (!_op->is_completed());
// This pairs up with the release store in do_handshake(). It prevents future
// loads from floating above the load of _pending_threads in is_completed()
// and thus prevents reading stale data modified in the handshake closure
// by the Handshakee.
OrderAccess::acquire();
log_handshake_info(start_time_ns, _op->name(), number_of_threads_issued, emitted_handshakes_executed);
}
VMOp_Type type() const { return VMOp_HandshakeAllThreads; }
};
void HandshakeOperation::prepare(JavaThread* current_target, Thread* executing_thread) {
if (current_target->is_terminated()) {
// Will never execute any handshakes on this thread.
return;
}
if (current_target != executing_thread) {
// Only when the target is not executing the handshake itself.
StackWatermarkSet::start_processing(current_target, StackWatermarkKind::gc);
}
if (_requester != NULL && _requester != executing_thread && _requester->is_Java_thread()) {
// The handshake closure may contain oop Handles from the _requester.
// We must make sure we can use them.
StackWatermarkSet::start_processing(JavaThread::cast(_requester), StackWatermarkKind::gc);
}
}
void HandshakeOperation::do_handshake(JavaThread* thread) {
jlong start_time_ns = 0;
if (log_is_enabled(Debug, handshake, task)) {
start_time_ns = os::javaTimeNanos();
}
// Only actually execute the operation for non terminated threads.
if (!thread->is_terminated()) {
_handshake_cl->do_thread(thread);
}
if (start_time_ns != 0) {
jlong completion_time = os::javaTimeNanos() - start_time_ns;
log_debug(handshake, task)("Operation: %s for thread " PTR_FORMAT ", is_vm_thread: %s, completed in " JLONG_FORMAT " ns",
name(), p2i(thread), BOOL_TO_STR(Thread::current()->is_VM_thread()), completion_time);
}
// Inform VMThread/Handshaker that we have completed the operation.
// When this is executed by the Handshakee we need a release store
// here to make sure memory operations executed in the handshake
// closure are visible to the VMThread/Handshaker after it reads
// that the operation has completed.
Atomic::dec(&_pending_threads);
// Trailing fence, used to make sure removal of the operation strictly
// happened after we completed the operation.
// It is no longer safe to refer to 'this' as the VMThread/Handshaker may have destroyed this operation
}
void Handshake::execute(HandshakeClosure* hs_cl) {
HandshakeOperation cto(hs_cl, NULL, Thread::current());
VM_HandshakeAllThreads handshake(&cto);
VMThread::execute(&handshake);
}
void Handshake::execute(HandshakeClosure* hs_cl, JavaThread* target) {
// tlh == nullptr means we rely on a ThreadsListHandle somewhere
// in the caller's context (and we sanity check for that).
Handshake::execute(hs_cl, nullptr, target);
}
void Handshake::execute(HandshakeClosure* hs_cl, ThreadsListHandle* tlh, JavaThread* target) {
JavaThread* self = JavaThread::current();
HandshakeOperation op(hs_cl, target, Thread::current());
jlong start_time_ns = os::javaTimeNanos();
guarantee(target != nullptr, "must be");
if (tlh == nullptr) {
guarantee(Thread::is_JavaThread_protected_by_TLH(target),
"missing ThreadsListHandle in calling context.");
target->handshake_state()->add_operation(&op);
} else if (tlh->includes(target)) {
target->handshake_state()->add_operation(&op);
} else {
char buf[128];
jio_snprintf(buf, sizeof(buf), "(thread= " INTPTR_FORMAT " dead)", p2i(target));
log_handshake_info(start_time_ns, op.name(), 0, 0, buf);
return;
}
// Separate the arming of the poll in add_operation() above from
// the read of JavaThread state in the try_process() call below.
if (UseSystemMemoryBarrier) {
SystemMemoryBarrier::emit();
}
// Keeps count on how many of own emitted handshakes
// this thread execute.
int emitted_handshakes_executed = 0;
HandshakeSpinYield hsy(start_time_ns);
while (!op.is_completed()) {
HandshakeState::ProcessResult pr = target->handshake_state()->try_process(&op);
if (pr == HandshakeState::_succeeded) {
emitted_handshakes_executed++;
}
if (op.is_completed()) {
break;
}
// Check if handshake operation has timed out
check_handshake_timeout(start_time_ns, &op, target);
hsy.add_result(pr);
// Check for pending handshakes to avoid possible deadlocks where our
// target is trying to handshake us.
if (SafepointMechanism::should_process(self)) {
// Will not suspend here.
ThreadBlockInVM tbivm(self);
}
hsy.process();
}
// This pairs up with the release store in do_handshake(). It prevents future
// loads from floating above the load of _pending_threads in is_completed()
// and thus prevents reading stale data modified in the handshake closure
// by the Handshakee.
OrderAccess::acquire();
log_handshake_info(start_time_ns, op.name(), 1, emitted_handshakes_executed);
}
void Handshake::execute(AsyncHandshakeClosure* hs_cl, JavaThread* target) {
jlong start_time_ns = os::javaTimeNanos();
AsyncHandshakeOperation* op = new AsyncHandshakeOperation(hs_cl, target, start_time_ns);
guarantee(target != nullptr, "must be");
Thread* current = Thread::current();
if (current != target) {
// Another thread is handling the request and it must be protecting
// the target.
guarantee(Thread::is_JavaThread_protected_by_TLH(target),
"missing ThreadsListHandle in calling context.");
}
// Implied else:
// The target is handling the request itself so it can't be dead.
target->handshake_state()->add_operation(op);
}
// Filters
static bool non_self_executable_filter(HandshakeOperation* op) {
return !op->is_async();
}
static bool no_async_exception_filter(HandshakeOperation* op) {
return !op->is_async_exception();
}
static bool async_exception_filter(HandshakeOperation* op) {
return op->is_async_exception();
}
static bool no_suspend_no_async_exception_filter(HandshakeOperation* op) {
return !op->is_suspend() && !op->is_async_exception();
}
static bool all_ops_filter(HandshakeOperation* op) {
return true;
}
HandshakeState::HandshakeState(JavaThread* target) :
_handshakee(target),
_queue(),
_lock(Monitor::nosafepoint, "HandshakeState_lock"),
_active_handshaker(),
_async_exceptions_blocked(false),
_suspended(false),
_async_suspend_handshake(false) {
}
HandshakeState::~HandshakeState() {
while (has_operation()) {
HandshakeOperation* op = _queue.pop(all_ops_filter);
guarantee(op->is_async(), "Only async operations may still be present on queue");
delete op;
}
}
void HandshakeState::add_operation(HandshakeOperation* op) {
// Adds are done lock free and so is arming.
_queue.push(op);
SafepointMechanism::arm_local_poll_release(_handshakee);
}
bool HandshakeState::operation_pending(HandshakeOperation* op) {
MutexLocker ml(&_lock, Mutex::_no_safepoint_check_flag);
MatchOp mo(op);
return _queue.contains(mo);
}
HandshakeOperation* HandshakeState::get_op_for_self(bool allow_suspend, bool check_async_exception) {
assert(_handshakee == Thread::current(), "Must be called by self");
assert(_lock.owned_by_self(), "Lock must be held");
assert(allow_suspend || !check_async_exception, "invalid case");
if (!allow_suspend) {
return _queue.peek(no_suspend_no_async_exception_filter);
} else if (check_async_exception && !_async_exceptions_blocked) {
return _queue.peek();
} else {
return _queue.peek(no_async_exception_filter);
}
}
bool HandshakeState::has_operation(bool allow_suspend, bool check_async_exception) {
MutexLocker ml(&_lock, Mutex::_no_safepoint_check_flag);
return get_op_for_self(allow_suspend, check_async_exception) != NULL;
}
bool HandshakeState::has_async_exception_operation() {
if (!has_operation()) return false;
MutexLocker ml(_lock.owned_by_self() ? NULL : &_lock, Mutex::_no_safepoint_check_flag);
return _queue.peek(async_exception_filter) != NULL;
}
void HandshakeState::clean_async_exception_operation() {
while (has_async_exception_operation()) {
MutexLocker ml(&_lock, Mutex::_no_safepoint_check_flag);
HandshakeOperation* op;
op = _queue.peek(async_exception_filter);
remove_op(op);
delete op;
}
}
bool HandshakeState::have_non_self_executable_operation() {
assert(_handshakee != Thread::current(), "Must not be called by self");
assert(_lock.owned_by_self(), "Lock must be held");
return _queue.contains(non_self_executable_filter);
}
HandshakeOperation* HandshakeState::get_op() {
assert(_handshakee != Thread::current(), "Must not be called by self");
assert(_lock.owned_by_self(), "Lock must be held");
return _queue.peek(non_self_executable_filter);
};
void HandshakeState::remove_op(HandshakeOperation* op) {
assert(_lock.owned_by_self(), "Lock must be held");
MatchOp mo(op);
HandshakeOperation* ret = _queue.pop(mo);
assert(ret == op, "Popped op must match requested op");
};
bool HandshakeState::process_by_self(bool allow_suspend, bool check_async_exception) {
assert(Thread::current() == _handshakee, "should call from _handshakee");
assert(!_handshakee->is_terminated(), "should not be a terminated thread");
_handshakee->frame_anchor()->make_walkable();
// Threads shouldn't block if they are in the middle of printing, but...
ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
while (has_operation()) {
// Handshakes cannot safely safepoint. The exceptions to this rule are
// the asynchronous suspension and unsafe access error handshakes.
MutexLocker ml(&_lock, Mutex::_no_safepoint_check_flag);
HandshakeOperation* op = get_op_for_self(allow_suspend, check_async_exception);
if (op != NULL) {
assert(op->_target == NULL || op->_target == Thread::current(), "Wrong thread");
bool async = op->is_async();
log_trace(handshake)("Proc handshake %s " INTPTR_FORMAT " on " INTPTR_FORMAT " by self",
async ? "asynchronous" : "synchronous", p2i(op), p2i(_handshakee));
op->prepare(_handshakee, _handshakee);
if (!async) {
HandleMark hm(_handshakee);
PreserveExceptionMark pem(_handshakee);
op->do_handshake(_handshakee); // acquire, op removed after
remove_op(op);
} else {
// An asynchronous handshake may put the JavaThread in blocked state (safepoint safe).
// The destructor ~PreserveExceptionMark touches the exception oop so it must not be executed,
// since a safepoint may be in-progress when returning from the async handshake.
remove_op(op);
op->do_handshake(_handshakee);
log_handshake_info(((AsyncHandshakeOperation*)op)->start_time(), op->name(), 1, 0, "asynchronous");
delete op;
return true; // Must check for safepoints
}
} else {
return false;
}
}
return false;
}
bool HandshakeState::can_process_handshake() {
// handshake_safe may only be called with polls armed.
// Handshaker controls this by first claiming the handshake via claim_handshake().
return SafepointSynchronize::handshake_safe(_handshakee);
}
bool HandshakeState::possibly_can_process_handshake() {
// Note that this method is allowed to produce false positives.
if (_handshakee->is_terminated()) {
return true;
}
switch (_handshakee->thread_state()) {
case _thread_in_native:
// native threads are safe if they have no java stack or have walkable stack
return !_handshakee->has_last_Java_frame() || _handshakee->frame_anchor()->walkable();
case _thread_blocked:
return true;
default:
return false;
}
}
bool HandshakeState::claim_handshake() {
if (!_lock.try_lock()) {
return false;
}
// Operations are added lock free and then the poll is armed.
// If all handshake operations for the handshakee are finished and someone
// just adds an operation we may see it here. But if the handshakee is not
// armed yet it is not safe to proceed.
if (have_non_self_executable_operation()) {
OrderAccess::loadload(); // Matches the implicit storestore in add_operation()
if (SafepointMechanism::local_poll_armed(_handshakee)) {
return true;
}
}
_lock.unlock();
return false;
}
HandshakeState::ProcessResult HandshakeState::try_process(HandshakeOperation* match_op) {
if (!has_operation()) {
// JT has already cleared its handshake
return HandshakeState::_no_operation;
}
if (!possibly_can_process_handshake()) {
// JT is observed in an unsafe state, it must notice the handshake itself
return HandshakeState::_not_safe;
}
// Claim the mutex if there still an operation to be executed.
if (!claim_handshake()) {
return HandshakeState::_claim_failed;
}
// If we own the mutex at this point and while owning the mutex we
// can observe a safe state the thread cannot possibly continue without
// getting caught by the mutex.
if (!can_process_handshake()) {
_lock.unlock();
return HandshakeState::_not_safe;
}
Thread* current_thread = Thread::current();
HandshakeOperation* op = get_op();
assert(op != NULL, "Must have an op");
assert(SafepointMechanism::local_poll_armed(_handshakee), "Must be");
assert(op->_target == NULL || _handshakee == op->_target, "Wrong thread");
log_trace(handshake)("Processing handshake " INTPTR_FORMAT " by %s(%s)", p2i(op),
op == match_op ? "handshaker" : "cooperative",
current_thread->is_VM_thread() ? "VM Thread" : "JavaThread");
op->prepare(_handshakee, current_thread);
set_active_handshaker(current_thread);
op->do_handshake(_handshakee); // acquire, op removed after
set_active_handshaker(NULL);
remove_op(op);
_lock.unlock();
log_trace(handshake)("%s(" INTPTR_FORMAT ") executed an op for JavaThread: " INTPTR_FORMAT " %s target op: " INTPTR_FORMAT,
current_thread->is_VM_thread() ? "VM Thread" : "JavaThread",
p2i(current_thread), p2i(_handshakee),
op == match_op ? "including" : "excluding", p2i(match_op));
return op == match_op ? HandshakeState::_succeeded : HandshakeState::_processed;
}
void HandshakeState::do_self_suspend() {
assert(Thread::current() == _handshakee, "should call from _handshakee");
assert(_lock.owned_by_self(), "Lock must be held");
assert(!_handshakee->has_last_Java_frame() || _handshakee->frame_anchor()->walkable(), "should have walkable stack");
assert(_handshakee->thread_state() == _thread_blocked, "Caller should have transitioned to _thread_blocked");
while (is_suspended()) {
log_trace(thread, suspend)("JavaThread:" INTPTR_FORMAT " suspended", p2i(_handshakee));
_lock.wait_without_safepoint_check();
}
log_trace(thread, suspend)("JavaThread:" INTPTR_FORMAT " resumed", p2i(_handshakee));
}
// This is the closure that prevents a suspended JavaThread from
// escaping the suspend request.
class ThreadSelfSuspensionHandshake : public AsyncHandshakeClosure {
public:
ThreadSelfSuspensionHandshake() : AsyncHandshakeClosure("ThreadSelfSuspensionHandshake") {}
void do_thread(Thread* thr) {
JavaThread* current = JavaThread::cast(thr);
assert(current == Thread::current(), "Must be self executed.");
JavaThreadState jts = current->thread_state();
current->set_thread_state(_thread_blocked);
current->handshake_state()->do_self_suspend();
current->set_thread_state(jts);
current->handshake_state()->set_async_suspend_handshake(false);
}
virtual bool is_suspend() { return true; }
};
bool HandshakeState::suspend_with_handshake() {
assert(_handshakee->threadObj() != NULL, "cannot suspend with a NULL threadObj");
if (_handshakee->is_exiting()) {
log_trace(thread, suspend)("JavaThread:" INTPTR_FORMAT " exiting", p2i(_handshakee));
return false;
}
if (has_async_suspend_handshake()) {
if (is_suspended()) {
// Target is already suspended.
log_trace(thread, suspend)("JavaThread:" INTPTR_FORMAT " already suspended", p2i(_handshakee));
return false;
} else {
// Target is going to wake up and leave suspension.
// Let's just stop the thread from doing that.
log_trace(thread, suspend)("JavaThread:" INTPTR_FORMAT " re-suspended", p2i(_handshakee));
set_suspended(true);
return true;
}
}
// no suspend request
assert(!is_suspended(), "cannot be suspended without a suspend request");
// Thread is safe, so it must execute the request, thus we can count it as suspended
// from this point.
set_suspended(true);
set_async_suspend_handshake(true);
log_trace(thread, suspend)("JavaThread:" INTPTR_FORMAT " suspended, arming ThreadSuspension", p2i(_handshakee));
ThreadSelfSuspensionHandshake* ts = new ThreadSelfSuspensionHandshake();
Handshake::execute(ts, _handshakee);
return true;
}
// This is the closure that synchronously honors the suspend request.
class SuspendThreadHandshake : public HandshakeClosure {
bool _did_suspend;
public:
SuspendThreadHandshake() : HandshakeClosure("SuspendThread"), _did_suspend(false) {}
void do_thread(Thread* thr) {
JavaThread* target = JavaThread::cast(thr);
_did_suspend = target->handshake_state()->suspend_with_handshake();
}
bool did_suspend() { return _did_suspend; }
};
bool HandshakeState::suspend() {
JVMTI_ONLY(assert(!_handshakee->is_in_VTMS_transition(), "no suspend allowed in VTMS transition");)
JavaThread* self = JavaThread::current();
if (_handshakee == self) {
// If target is the current thread we can bypass the handshake machinery
// and just suspend directly
ThreadBlockInVM tbivm(self);
MutexLocker ml(&_lock, Mutex::_no_safepoint_check_flag);
set_suspended(true);
do_self_suspend();
return true;
} else {
SuspendThreadHandshake st;
Handshake::execute(&st, _handshakee);
return st.did_suspend();
}
}
bool HandshakeState::resume() {
if (!is_suspended()) {
return false;
}
MutexLocker ml(&_lock, Mutex::_no_safepoint_check_flag);
if (!is_suspended()) {
assert(!_handshakee->is_suspended(), "cannot be suspended without a suspend request");
return false;
}
// Resume the thread.
set_suspended(false);
_lock.notify();
return true;
}
void HandshakeState::handle_unsafe_access_error() {
if (is_suspended()) {
// A suspend handshake was added to the queue after the
// unsafe access error. Since the suspender has already
// considered this JT as suspended and assumes it won't go
// back to Java until resumed we cannot create the exception
// object yet. Add a new unsafe access error operation to
// the end of the queue and try again in the next attempt.
Handshake::execute(new UnsafeAccessErrorHandshake(), _handshakee);
log_info(handshake)("JavaThread " INTPTR_FORMAT " skipping unsafe access processing due to suspend.", p2i(_handshakee));
return;
}
// Release the handshake lock before constructing the oop to
// avoid deadlocks since that can block. This will allow the
// JavaThread to execute normally as if it was outside a handshake.
// We will reacquire the handshake lock at return from ~MutexUnlocker.
MutexUnlocker ml(&_lock, Mutex::_no_safepoint_check_flag);
// We may be at method entry which requires we save the do-not-unlock flag.
UnlockFlagSaver fs(_handshakee);
Handle h_exception = Exceptions::new_exception(_handshakee, vmSymbols::java_lang_InternalError(), "a fault occurred in an unsafe memory access operation");
if (h_exception()->is_a(vmClasses::InternalError_klass())) {
java_lang_InternalError::set_during_unsafe_access(h_exception());
}
_handshakee->handle_async_exception(h_exception());
}
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