1/*
2 * Copyright (c) 2017, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25#include "precompiled.hpp"
26#include "logging/log.hpp"
27#include "logging/logStream.hpp"
28#include "memory/resourceArea.hpp"
29#include "runtime/handshake.hpp"
30#include "runtime/interfaceSupport.inline.hpp"
31#include "runtime/orderAccess.hpp"
32#include "runtime/osThread.hpp"
33#include "runtime/semaphore.inline.hpp"
34#include "runtime/task.hpp"
35#include "runtime/timerTrace.hpp"
36#include "runtime/thread.hpp"
37#include "runtime/vmThread.hpp"
38#include "utilities/formatBuffer.hpp"
39#include "utilities/preserveException.hpp"
40
41class HandshakeOperation: public StackObj {
42public:
43 virtual void do_handshake(JavaThread* thread) = 0;
44};
45
46class HandshakeThreadsOperation: public HandshakeOperation {
47 static Semaphore _done;
48 ThreadClosure* _thread_cl;
49
50public:
51 HandshakeThreadsOperation(ThreadClosure* cl) : _thread_cl(cl) {}
52 void do_handshake(JavaThread* thread);
53 bool thread_has_completed() { return _done.trywait(); }
54
55#ifdef ASSERT
56 void check_state() {
57 assert(!_done.trywait(), "Must be zero");
58 }
59#endif
60};
61
62Semaphore HandshakeThreadsOperation::_done(0);
63
64class VM_Handshake: public VM_Operation {
65 const jlong _handshake_timeout;
66 public:
67 bool evaluate_at_safepoint() const { return false; }
68
69 bool evaluate_concurrently() const { return false; }
70
71 protected:
72 HandshakeThreadsOperation* const _op;
73
74 VM_Handshake(HandshakeThreadsOperation* op) :
75 _handshake_timeout(TimeHelper::millis_to_counter(HandshakeTimeout)), _op(op) {}
76
77 void set_handshake(JavaThread* target) {
78 target->set_handshake_operation(_op);
79 }
80
81 // This method returns true for threads completed their operation
82 // and true for threads canceled their operation.
83 // A cancellation can happen if the thread is exiting.
84 bool poll_for_completed_thread() { return _op->thread_has_completed(); }
85
86 bool handshake_has_timed_out(jlong start_time);
87 static void handle_timeout();
88};
89
90bool VM_Handshake::handshake_has_timed_out(jlong start_time) {
91 // Check if handshake operation has timed out
92 if (_handshake_timeout > 0) {
93 return os::elapsed_counter() >= (start_time + _handshake_timeout);
94 }
95 return false;
96}
97
98void VM_Handshake::handle_timeout() {
99 LogStreamHandle(Warning, handshake) log_stream;
100 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
101 if (thr->has_handshake()) {
102 log_stream.print("Thread " PTR_FORMAT " has not cleared its handshake op", p2i(thr));
103 thr->print_thread_state_on(&log_stream);
104 }
105 }
106 log_stream.flush();
107 fatal("Handshake operation timed out");
108}
109
110class VM_HandshakeOneThread: public VM_Handshake {
111 JavaThread* _target;
112 bool _thread_alive;
113 public:
114 VM_HandshakeOneThread(HandshakeThreadsOperation* op, JavaThread* target) :
115 VM_Handshake(op), _target(target), _thread_alive(false) {}
116
117 void doit() {
118 DEBUG_ONLY(_op->check_state();)
119 TraceTime timer("Performing single-target operation (vmoperation doit)", TRACETIME_LOG(Info, handshake));
120
121 ThreadsListHandle tlh;
122 if (tlh.includes(_target)) {
123 set_handshake(_target);
124 _thread_alive = true;
125 } else {
126 return;
127 }
128
129 log_trace(handshake)("Thread signaled, begin processing by VMThtread");
130 jlong start_time = os::elapsed_counter();
131 do {
132 if (handshake_has_timed_out(start_time)) {
133 handle_timeout();
134 }
135
136 // We need to re-think this with SMR ThreadsList.
137 // There is an assumption in the code that the Threads_lock should be
138 // locked during certain phases.
139 {
140 MutexLocker ml(Threads_lock, Mutex::_no_safepoint_check_flag);
141 _target->handshake_process_by_vmthread();
142 }
143 } while (!poll_for_completed_thread());
144 DEBUG_ONLY(_op->check_state();)
145 }
146
147 VMOp_Type type() const { return VMOp_HandshakeOneThread; }
148
149 bool thread_alive() const { return _thread_alive; }
150};
151
152class VM_HandshakeAllThreads: public VM_Handshake {
153 public:
154 VM_HandshakeAllThreads(HandshakeThreadsOperation* op) : VM_Handshake(op) {}
155
156 void doit() {
157 DEBUG_ONLY(_op->check_state();)
158 TraceTime timer("Performing operation (vmoperation doit)", TRACETIME_LOG(Info, handshake));
159
160 JavaThreadIteratorWithHandle jtiwh;
161 int number_of_threads_issued = 0;
162 for (JavaThread *thr = jtiwh.next(); thr != NULL; thr = jtiwh.next()) {
163 set_handshake(thr);
164 number_of_threads_issued++;
165 }
166
167 if (number_of_threads_issued < 1) {
168 log_debug(handshake)("No threads to handshake.");
169 return;
170 }
171
172 log_debug(handshake)("Threads signaled, begin processing blocked threads by VMThtread");
173 const jlong start_time = os::elapsed_counter();
174 int number_of_threads_completed = 0;
175 do {
176 // Check if handshake operation has timed out
177 if (handshake_has_timed_out(start_time)) {
178 handle_timeout();
179 }
180
181 // Have VM thread perform the handshake operation for blocked threads.
182 // Observing a blocked state may of course be transient but the processing is guarded
183 // by semaphores and we optimistically begin by working on the blocked threads
184 {
185 // We need to re-think this with SMR ThreadsList.
186 // There is an assumption in the code that the Threads_lock should
187 // be locked during certain phases.
188 jtiwh.rewind();
189 MutexLocker ml(Threads_lock, Mutex::_no_safepoint_check_flag);
190 for (JavaThread *thr = jtiwh.next(); thr != NULL; thr = jtiwh.next()) {
191 // A new thread on the ThreadsList will not have an operation,
192 // hence it is skipped in handshake_process_by_vmthread.
193 thr->handshake_process_by_vmthread();
194 }
195 }
196
197 while (poll_for_completed_thread()) {
198 // Includes canceled operations by exiting threads.
199 number_of_threads_completed++;
200 }
201
202 } while (number_of_threads_issued > number_of_threads_completed);
203 assert(number_of_threads_issued == number_of_threads_completed, "Must be the same");
204 DEBUG_ONLY(_op->check_state();)
205 }
206
207 VMOp_Type type() const { return VMOp_HandshakeAllThreads; }
208};
209
210class VM_HandshakeFallbackOperation : public VM_Operation {
211 ThreadClosure* _thread_cl;
212 Thread* _target_thread;
213 bool _all_threads;
214 bool _thread_alive;
215public:
216 VM_HandshakeFallbackOperation(ThreadClosure* cl) :
217 _thread_cl(cl), _target_thread(NULL), _all_threads(true), _thread_alive(true) {}
218 VM_HandshakeFallbackOperation(ThreadClosure* cl, Thread* target) :
219 _thread_cl(cl), _target_thread(target), _all_threads(false), _thread_alive(false) {}
220
221 void doit() {
222 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
223 if (_all_threads || t == _target_thread) {
224 if (t == _target_thread) {
225 _thread_alive = true;
226 }
227 _thread_cl->do_thread(t);
228 }
229 }
230 }
231
232 VMOp_Type type() const { return VMOp_HandshakeFallback; }
233 bool thread_alive() const { return _thread_alive; }
234};
235
236void HandshakeThreadsOperation::do_handshake(JavaThread* thread) {
237 ResourceMark rm;
238 FormatBufferResource message("Operation for thread " PTR_FORMAT ", is_vm_thread: %s",
239 p2i(thread), BOOL_TO_STR(Thread::current()->is_VM_thread()));
240 TraceTime timer(message, TRACETIME_LOG(Debug, handshake, task));
241
242 // Only actually execute the operation for non terminated threads.
243 if (!thread->is_terminated()) {
244 _thread_cl->do_thread(thread);
245 }
246
247 // Use the semaphore to inform the VM thread that we have completed the operation
248 _done.signal();
249}
250
251void Handshake::execute(ThreadClosure* thread_cl) {
252 if (ThreadLocalHandshakes) {
253 HandshakeThreadsOperation cto(thread_cl);
254 VM_HandshakeAllThreads handshake(&cto);
255 VMThread::execute(&handshake);
256 } else {
257 VM_HandshakeFallbackOperation op(thread_cl);
258 VMThread::execute(&op);
259 }
260}
261
262bool Handshake::execute(ThreadClosure* thread_cl, JavaThread* target) {
263 if (ThreadLocalHandshakes) {
264 HandshakeThreadsOperation cto(thread_cl);
265 VM_HandshakeOneThread handshake(&cto, target);
266 VMThread::execute(&handshake);
267 return handshake.thread_alive();
268 } else {
269 VM_HandshakeFallbackOperation op(thread_cl, target);
270 VMThread::execute(&op);
271 return op.thread_alive();
272 }
273}
274
275HandshakeState::HandshakeState() : _operation(NULL), _semaphore(1), _thread_in_process_handshake(false) {}
276
277void HandshakeState::set_operation(JavaThread* target, HandshakeOperation* op) {
278 _operation = op;
279 SafepointMechanism::arm_local_poll_release(target);
280}
281
282void HandshakeState::clear_handshake(JavaThread* target) {
283 _operation = NULL;
284 SafepointMechanism::disarm_if_needed(target, true /* release */);
285}
286
287void HandshakeState::process_self_inner(JavaThread* thread) {
288 assert(Thread::current() == thread, "should call from thread");
289 assert(!thread->is_terminated(), "should not be a terminated thread");
290
291 ThreadInVMForHandshake tivm(thread);
292 if (!_semaphore.trywait()) {
293 _semaphore.wait_with_safepoint_check(thread);
294 }
295 HandshakeOperation* op = OrderAccess::load_acquire(&_operation);
296 if (op != NULL) {
297 HandleMark hm(thread);
298 CautiouslyPreserveExceptionMark pem(thread);
299 // Disarm before execute the operation
300 clear_handshake(thread);
301 op->do_handshake(thread);
302 }
303 _semaphore.signal();
304}
305
306bool HandshakeState::vmthread_can_process_handshake(JavaThread* target) {
307 // handshake_safe may only be called with polls armed.
308 // VM thread controls this by first claiming the handshake via claim_handshake_for_vmthread.
309 return SafepointSynchronize::handshake_safe(target);
310}
311
312static bool possibly_vmthread_can_process_handshake(JavaThread* target) {
313 // An externally suspended thread cannot be resumed while the
314 // Threads_lock is held so it is safe.
315 // Note that this method is allowed to produce false positives.
316 assert(Threads_lock->owned_by_self(), "Not holding Threads_lock.");
317 if (target->is_ext_suspended()) {
318 return true;
319 }
320 if (target->is_terminated()) {
321 return true;
322 }
323 switch (target->thread_state()) {
324 case _thread_in_native:
325 // native threads are safe if they have no java stack or have walkable stack
326 return !target->has_last_Java_frame() || target->frame_anchor()->walkable();
327
328 case _thread_blocked:
329 return true;
330
331 default:
332 return false;
333 }
334}
335
336bool HandshakeState::claim_handshake_for_vmthread() {
337 if (!_semaphore.trywait()) {
338 return false;
339 }
340 if (has_operation()) {
341 return true;
342 }
343 _semaphore.signal();
344 return false;
345}
346
347void HandshakeState::process_by_vmthread(JavaThread* target) {
348 assert(Thread::current()->is_VM_thread(), "should call from vm thread");
349 // Threads_lock must be held here, but that is assert()ed in
350 // possibly_vmthread_can_process_handshake().
351
352 if (!has_operation()) {
353 // JT has already cleared its handshake
354 return;
355 }
356
357 if (!possibly_vmthread_can_process_handshake(target)) {
358 // JT is observed in an unsafe state, it must notice the handshake itself
359 return;
360 }
361
362 // Claim the semaphore if there still an operation to be executed.
363 if (!claim_handshake_for_vmthread()) {
364 return;
365 }
366
367 // If we own the semaphore at this point and while owning the semaphore
368 // can observe a safe state the thread cannot possibly continue without
369 // getting caught by the semaphore.
370 if (vmthread_can_process_handshake(target)) {
371 guarantee(!_semaphore.trywait(), "we should already own the semaphore");
372 _operation->do_handshake(target);
373 // Disarm after VM thread have executed the operation.
374 clear_handshake(target);
375 // Release the thread
376 }
377
378 _semaphore.signal();
379}
380