1 /*
   2  * Copyright (c) 2017, 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 "memory/allocation.inline.hpp"
  27 #include "runtime/thread.inline.hpp"
  28 #include "runtime/threadSMR.hpp"
  29 #include "services/threadService.hpp"
  30 
  31 // 'entries + 1' so we always have at least one entry.
  32 ThreadsList::ThreadsList(int entries) : _length(entries), _threads(NEW_C_HEAP_ARRAY(JavaThread*, entries + 1, mtGC)), _next_list(NULL) {
  33   *(JavaThread**)(_threads + entries) = NULL;  // Make sure the extra entry is NULL.
  34 }
  35 
  36 ThreadsList::~ThreadsList() {
  37   FREE_C_HEAP_ARRAY(JavaThread*, _threads);
  38 }
  39 
  40 ThreadsListSetter::~ThreadsListSetter() {
  41   if (_target_needs_release) {
  42     // The hazard ptr in the target needs to be released.
  43     Threads::release_stable_list(_target);
  44   }
  45 }
  46 
  47 void ThreadsListSetter::set() {
  48   assert(_target->get_threads_hazard_ptr() == NULL, "hazard ptr should not already be set");
  49   (void) Threads::acquire_stable_list(_target, /* is_ThreadsListSetter */ true);
  50   _target_needs_release = true;
  51 }
  52 
  53 ThreadsListHandle::ThreadsListHandle(Thread *self) : _list(Threads::acquire_stable_list(self, /* is_ThreadsListSetter */ false)), _self(self) {
  54   assert(self == Thread::current(), "sanity check");
  55   if (EnableThreadSMRStatistics) {
  56     _timer.start();
  57   }
  58 }
  59 
  60 ThreadsListHandle::~ThreadsListHandle() {
  61   Threads::release_stable_list(_self);
  62   if (EnableThreadSMRStatistics) {
  63     _timer.stop();
  64     jint millis = (jint)_timer.milliseconds();
  65     Threads::inc_smr_tlh_cnt();
  66     Threads::add_smr_tlh_times(millis);
  67     Threads::update_smr_tlh_time_max(millis);
  68   }
  69 }
  70 
  71 // Convert an internal thread reference to a JavaThread found on the
  72 // associated ThreadsList. This ThreadsListHandle "protects" the
  73 // returned JavaThread *.
  74 //
  75 // If thread_oop_p is not NULL, then the caller wants to use the oop
  76 // after this call so the oop is returned. On success, *jt_pp is set
  77 // to the converted JavaThread * and true is returned. On error,
  78 // returns false.
  79 //
  80 bool ThreadsListHandle::cv_internal_thread_to_JavaThread(jobject jthread,
  81                                                          JavaThread ** jt_pp,
  82                                                          oop * thread_oop_p) {
  83   assert(this->list() != NULL, "must have a ThreadsList");
  84   assert(jt_pp != NULL, "must have a return JavaThread pointer");
  85   // thread_oop_p is optional so no assert()
  86 
  87   // The JVM_* interfaces don't allow a NULL thread parameter; JVM/TI
  88   // allows a NULL thread parameter to signify "current thread" which
  89   // allows us to avoid calling cv_external_thread_to_JavaThread().
  90   // The JVM_* interfaces have no such leeway.
  91 
  92   oop thread_oop = JNIHandles::resolve_non_null(jthread);
  93   // Looks like an oop at this point.
  94   if (thread_oop_p != NULL) {
  95     // Return the oop to the caller; the caller may still want
  96     // the oop even if this function returns false.
  97     *thread_oop_p = thread_oop;
  98   }
  99 
 100   JavaThread *java_thread = java_lang_Thread::thread(thread_oop);
 101   if (java_thread == NULL) {
 102     // The java.lang.Thread does not contain a JavaThread * so it has
 103     // not yet run or it has died.
 104     return false;
 105   }
 106   // Looks like a live JavaThread at this point.
 107 
 108   if (java_thread != JavaThread::current()) {
 109     // jthread is not for the current JavaThread so have to verify
 110     // the JavaThread * against the ThreadsList.
 111     if (EnableThreadSMRExtraValidityChecks && !includes(java_thread)) {
 112       // Not on the JavaThreads list so it is not alive.
 113       return false;
 114     }
 115   }
 116 
 117   // Return a live JavaThread that is "protected" by the
 118   // ThreadsListHandle in the caller.
 119   *jt_pp = java_thread;
 120   return true;
 121 }