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24 
25 #ifndef SHARE_GC_CMS_CONCURRENTMARKSWEEPTHREAD_HPP
26 #define SHARE_GC_CMS_CONCURRENTMARKSWEEPTHREAD_HPP
27 
28 #include "gc/cms/concurrentMarkSweepGeneration.hpp"
29 #include "gc/shared/concurrentGCThread.hpp"
30 #include "runtime/thread.hpp"
31 
32 class ConcurrentMarkSweepGeneration;
33 class CMSCollector;
34 
35 // The Concurrent Mark Sweep GC Thread
36 class ConcurrentMarkSweepThread: public ConcurrentGCThread {
37   friend class VMStructs;
38   friend class ConcurrentMarkSweepGeneration;   // XXX should remove friendship
39   friend class CMSCollector;
40 
41  private:
42   static ConcurrentMarkSweepThread* _cmst;
43   static CMSCollector*              _collector;
44 
45   enum CMS_flag_type {
46     CMS_nil             = NoBits,
47     CMS_cms_wants_token = nth_bit(0),
48     CMS_cms_has_token   = nth_bit(1),
49     CMS_vm_wants_token  = nth_bit(2),
50     CMS_vm_has_token    = nth_bit(3)
51   };
52 
53   static int _CMS_flag;
54 
CMS_flag_is_set(int b)55   static bool CMS_flag_is_set(int b)        { return (_CMS_flag & b) != 0;   }
set_CMS_flag(int b)56   static bool set_CMS_flag(int b)           { return (_CMS_flag |= b) != 0;  }
clear_CMS_flag(int b)57   static bool clear_CMS_flag(int b)         { return (_CMS_flag &= ~b) != 0; }
58   void sleepBeforeNextCycle();
59 
60   // CMS thread should yield for a young gen collection and direct allocations
61   static char _pad_1[64 - sizeof(jint)];    // prevent cache-line sharing
62   static volatile jint _pending_yields;
63   static char _pad_2[64 - sizeof(jint)];    // prevent cache-line sharing
64 
65   // debugging
66   void verify_ok_to_terminate() const PRODUCT_RETURN;
67 
68   void run_service();
69   void stop_service();
70 
71  public:
72   // Constructor
73   ConcurrentMarkSweepThread(CMSCollector* collector);
74 
75   static void threads_do(ThreadClosure* tc);
76 
77   // Printing
78   static void print_all_on(outputStream* st);
print_all()79   static void print_all()                             { print_all_on(tty); }
80 
81   // Returns the CMS Thread
cmst()82   static ConcurrentMarkSweepThread* cmst()    { return _cmst; }
collector()83   static CMSCollector*         collector()    { return _collector;  }
84 
85   // Create and start the CMS Thread, or stop it on shutdown
86   static ConcurrentMarkSweepThread* start(CMSCollector* collector);
87 
88   // Synchronization using CMS token
89   static void synchronize(bool is_cms_thread);
90   static void desynchronize(bool is_cms_thread);
vm_thread_has_cms_token()91   static bool vm_thread_has_cms_token() {
92     return CMS_flag_is_set(CMS_vm_has_token);
93   }
cms_thread_has_cms_token()94   static bool cms_thread_has_cms_token() {
95     return CMS_flag_is_set(CMS_cms_has_token);
96   }
vm_thread_wants_cms_token()97   static bool vm_thread_wants_cms_token() {
98     return CMS_flag_is_set(CMS_vm_wants_token);
99   }
cms_thread_wants_cms_token()100   static bool cms_thread_wants_cms_token() {
101     return CMS_flag_is_set(CMS_cms_wants_token);
102   }
103 
104   // Wait on CMS lock until the next synchronous GC
105   // or given timeout, whichever is earlier. A timeout value
106   // of 0 indicates that there is no upper bound on the wait time.
107   // A concurrent full gc request terminates the wait.
108   void wait_on_cms_lock(long t_millis);
109 
110   // Wait on CMS lock until the next synchronous GC
111   // or given timeout, whichever is earlier. A timeout value
112   // of 0 indicates that there is no upper bound on the wait time.
113   // A concurrent full gc request terminates the wait.
114   void wait_on_cms_lock_for_scavenge(long t_millis);
115 
116   // The CMS thread will yield during the work portion of its cycle
117   // only when requested to.
118   // A synchronous request is used for young gen collections and
119   // for direct allocations.  The requesting thread increments
120   // _pending_yields at the beginning of an operation, and decrements
121   // _pending_yields when that operation is completed.
122   // In turn, the CMS thread yields when _pending_yields is positive,
123   // and continues to yield until the value reverts to 0.
124 
increment_pending_yields()125   static void increment_pending_yields()   {
126     Atomic::inc(&_pending_yields);
127     assert(_pending_yields >= 0, "can't be negative");
128   }
decrement_pending_yields()129   static void decrement_pending_yields()   {
130     Atomic::dec(&_pending_yields);
131     assert(_pending_yields >= 0, "can't be negative");
132   }
should_yield()133   static bool should_yield()   { return _pending_yields > 0; }
134 };
135 
136 // For scoped increment/decrement of (synchronous) yield requests
137 class CMSSynchronousYieldRequest: public StackObj {
138  public:
CMSSynchronousYieldRequest()139   CMSSynchronousYieldRequest() {
140     ConcurrentMarkSweepThread::increment_pending_yields();
141   }
~CMSSynchronousYieldRequest()142   ~CMSSynchronousYieldRequest() {
143     ConcurrentMarkSweepThread::decrement_pending_yields();
144   }
145 };
146 
147 // Used to emit a warning in case of unexpectedly excessive
148 // looping (in "apparently endless loops") in CMS code.
149 class CMSLoopCountWarn: public StackObj {
150  private:
151   const char* _src;
152   const char* _msg;
153   const intx  _threshold;
154   intx        _ticks;
155 
156  public:
CMSLoopCountWarn(const char * src,const char * msg,const intx threshold)157   inline CMSLoopCountWarn(const char* src, const char* msg,
158                           const intx threshold) :
159     _src(src), _msg(msg), _threshold(threshold), _ticks(0) { }
160 
tick()161   inline void tick() {
162     _ticks++;
163     if (CMSLoopWarn && _ticks % _threshold == 0) {
164       log_warning(gc)("%s has looped " INTX_FORMAT " times %s", _src, _ticks, _msg);
165     }
166   }
167 };
168 
169 #endif // SHARE_GC_CMS_CONCURRENTMARKSWEEPTHREAD_HPP
170