1 /*
   2  * Copyright (c) 1998, 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 #ifndef SHARE_RUNTIME_VMTHREAD_HPP
  26 #define SHARE_RUNTIME_VMTHREAD_HPP
  27 
  28 #include "runtime/perfData.hpp"
  29 #include "runtime/thread.hpp"
  30 #include "runtime/task.hpp"
  31 #include "runtime/vmOperations.hpp"
  32 
  33 //
  34 // Prioritized queue of VM operations.
  35 //
  36 // Encapsulates both queue management and
  37 // and priority policy
  38 //
  39 class VMOperationQueue : public CHeapObj<mtInternal> {
  40  private:
  41   enum Priorities {
  42      SafepointPriority, // Highest priority (operation executed at a safepoint)
  43      MediumPriority,    // Medium priority
  44      nof_priorities
  45   };
  46 
  47   // We maintain a doubled linked list, with explicit count.
  48   int           _queue_length[nof_priorities];
  49   int           _queue_counter;
  50   VM_Operation* _queue       [nof_priorities];
  51   // we also allow the vmThread to register the ops it has drained so we
  52   // can scan them from oops_do
  53   VM_Operation* _drain_list;
  54 
  55   // Double-linked non-empty list insert.
  56   void insert(VM_Operation* q,VM_Operation* n);
  57   void unlink(VM_Operation* q);
  58 
  59   // Basic queue manipulation
  60   bool queue_empty                (int prio);
  61   void queue_add_front            (int prio, VM_Operation *op);
  62   void queue_add_back             (int prio, VM_Operation *op);
  63   VM_Operation* queue_remove_front(int prio);
  64   void queue_oops_do(int queue, OopClosure* f);
  65   void drain_list_oops_do(OopClosure* f);
  66   VM_Operation* queue_drain(int prio);
  67   // lock-free query: may return the wrong answer but must not break
  68   bool queue_peek(int prio) { return _queue_length[prio] > 0; }
  69 
  70  public:
  71   VMOperationQueue();
  72 
  73   // Highlevel operations. Encapsulates policy
  74   bool add(VM_Operation *op);
  75   VM_Operation* remove_next();                        // Returns next or null
  76   VM_Operation* remove_next_at_safepoint_priority()   { return queue_remove_front(SafepointPriority); }
  77   VM_Operation* drain_at_safepoint_priority() { return queue_drain(SafepointPriority); }
  78   void set_drain_list(VM_Operation* list) { _drain_list = list; }
  79   bool peek_at_safepoint_priority() { return queue_peek(SafepointPriority); }
  80 
  81   // GC support
  82   void oops_do(OopClosure* f);
  83 
  84   void verify_queue(int prio) PRODUCT_RETURN;
  85 };
  86 
  87 
  88 // VM operation timeout handling: warn or abort the VM when VM operation takes
  89 // too long. Periodic tasks do not participate in safepoint protocol, and therefore
  90 // can fire when application threads are stopped.
  91 
  92 class VMOperationTimeoutTask : public PeriodicTask {
  93 private:
  94   volatile int _armed;
  95   jlong _arm_time;
  96 
  97 public:
  98   VMOperationTimeoutTask(size_t interval_time) :
  99           PeriodicTask(interval_time), _armed(0), _arm_time(0) {}
 100 
 101   virtual void task();
 102 
 103   bool is_armed();
 104   void arm();
 105   void disarm();
 106 };
 107 
 108 //
 109 // A single VMThread (the primordial thread) spawns all other threads
 110 // and is itself used by other threads to offload heavy vm operations
 111 // like scavenge, garbage_collect etc.
 112 //
 113 
 114 class VMThread: public NamedThread {
 115  private:
 116   static ThreadPriority _current_priority;
 117 
 118   static bool _should_terminate;
 119   static bool _terminated;
 120   static Monitor * _terminate_lock;
 121   static PerfCounter* _perf_accumulated_vm_operation_time;
 122   static uint64_t _coalesced_count;
 123 
 124   static VMOperationTimeoutTask* _timeout_task;
 125 
 126   static VM_Operation* no_op_safepoint();
 127 
 128   void evaluate_operation(VM_Operation* op);
 129 
 130  public:
 131   // Constructor
 132   VMThread();
 133 
 134   // No destruction allowed
 135   ~VMThread() {
 136     guarantee(false, "VMThread deletion must fix the race with VM termination");
 137   }
 138 
 139 
 140   // Tester
 141   bool is_VM_thread() const                      { return true; }
 142   bool is_GC_thread() const                      { return true; }
 143 
 144   // The ever running loop for the VMThread
 145   void loop();
 146 
 147   // Called to stop the VM thread
 148   static void wait_for_vm_thread_exit();
 149   static bool should_terminate()                  { return _should_terminate; }
 150   static bool is_terminated()                     { return _terminated == true; }
 151 
 152   // Execution of vm operation
 153   static void execute(VM_Operation* op);
 154 
 155   // Returns the current vm operation if any.
 156   static VM_Operation* vm_operation()             { return _cur_vm_operation; }
 157   static VM_Operation::VMOp_Type vm_op_type()     { return _cur_vm_operation->type(); }
 158   static uint64_t get_coalesced_count()           { return _coalesced_count; }
 159 
 160   // Returns the single instance of VMThread.
 161   static VMThread* vm_thread()                    { return _vm_thread; }
 162 
 163   // GC support
 164   void oops_do(OopClosure* f, CodeBlobClosure* cf);
 165 
 166   void verify();
 167 
 168   // Performance measurement
 169   static PerfCounter* perf_accumulated_vm_operation_time()               { return _perf_accumulated_vm_operation_time; }
 170 
 171   // Entry for starting vm thread
 172   virtual void run();
 173 
 174   // Creations/Destructions
 175   static void create();
 176   static void destroy();
 177 
 178  private:
 179   // VM_Operation support
 180   static VM_Operation*     _cur_vm_operation;   // Current VM operation
 181   static VMOperationQueue* _vm_queue;           // Queue (w/ policy) of VM operations
 182 
 183   // Pointer to single-instance of VM thread
 184   static VMThread*     _vm_thread;
 185 };
 186 
 187 #endif // SHARE_RUNTIME_VMTHREAD_HPP