C++ GenCollectedHeap::total_collections方法代码示例

// VM operation to invoke a concurrent collection of a
// GenCollectedHeap heap.
void VM_GenCollectFullConcurrent::doit() {
  assert(Thread::current()->is_VM_thread(), "Should be VM thread");
  assert(GCLockerInvokesConcurrent || ExplicitGCInvokesConcurrent, "Unexpected");

  GenCollectedHeap* gch = GenCollectedHeap::heap();
  if (_gc_count_before == gch->total_collections()) {
    // The "full" of do_full_collection call below "forces"
    // a collection; the second arg, 0, below ensures that
    // only the young gen is collected. XXX In the future,
    // we'll probably need to have something in this interface
    // to say do this only if we are sure we will not bail
    // out to a full collection in this attempt, but that's
    // for the future.
    assert(SafepointSynchronize::is_at_safepoint(),
      "We can only be executing this arm of if at a safepoint");
    GCCauseSetter gccs(gch, _gc_cause);
    gch->do_full_collection(gch->must_clear_all_soft_refs(), GenCollectedHeap::YoungGen);
  } // Else no need for a foreground young gc
  assert((_gc_count_before < gch->total_collections()) ||
         (GCLocker::is_active() /* gc may have been skipped */
          && (_gc_count_before == gch->total_collections())),
         "total_collections() should be monotonically increasing");

  MutexLockerEx x(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
  assert(_full_gc_count_before <= gch->total_full_collections(), "Error");
  if (gch->total_full_collections() == _full_gc_count_before) {
    // Nudge the CMS thread to start a concurrent collection.
    CMSCollector::request_full_gc(_full_gc_count_before, _gc_cause);
  } else {
    assert(_full_gc_count_before < gch->total_full_collections(), "Error");
    FullGCCount_lock->notify_all();  // Inform the Java thread its work is done
  }
}

bool VM_GenCollectFullConcurrent::evaluate_at_safepoint() const {
  Thread* thr = Thread::current();
  assert(thr != NULL, "Unexpected tid");
  if (!thr->is_Java_thread()) {
    assert(thr->is_VM_thread(), "Expected to be evaluated by VM thread");
    GenCollectedHeap* gch = GenCollectedHeap::heap();
    if (_gc_count_before != gch->total_collections()) {
      // No need to do a young gc, we'll just nudge the CMS thread
      // in the doit() method above, to be executed soon.
      assert(_gc_count_before < gch->total_collections(),
             "total_collections() should be monotonically increasing");
      return false;  // no need for foreground young gc
    }
  }
  return true;       // may still need foreground young gc
}

// Wait until the next synchronous GC, a concurrent full gc request,
// or a timeout, whichever is earlier.
void ConcurrentMarkSweepThread::wait_on_cms_lock_for_scavenge(long t_millis) {
  // Wait time in millis or 0 value representing infinite wait for a scavenge
  assert(t_millis >= 0, "Wait time for scavenge should be 0 or positive");

  GenCollectedHeap* gch = GenCollectedHeap::heap();
  double start_time_secs = os::elapsedTime();
  double end_time_secs = start_time_secs + (t_millis / ((double) MILLIUNITS));

  // Total collections count before waiting loop
  unsigned int before_count;
  {
    MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
    before_count = gch->total_collections();
  }

  unsigned int loop_count = 0;

  while(!_should_terminate) {
    double now_time = os::elapsedTime();
    long wait_time_millis;

    if(t_millis != 0) {
      // New wait limit
      wait_time_millis = (long) ((end_time_secs - now_time) * MILLIUNITS);
      if(wait_time_millis <= 0) {
        // Wait time is over
        break;
      }
    } else {
      // No wait limit, wait if necessary forever
      wait_time_millis = 0;
    }

    // Wait until the next event or the remaining timeout
    {
      MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);

      if (_should_terminate || _collector->_full_gc_requested) {
        return;
      }
      set_CMS_flag(CMS_cms_wants_token);   // to provoke notifies
      assert(t_millis == 0 || wait_time_millis > 0, "Sanity");
      CGC_lock->wait(Mutex::_no_safepoint_check_flag, wait_time_millis);
      clear_CMS_flag(CMS_cms_wants_token);
      assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
             "Should not be set");
    }

    // Extra wait time check before entering the heap lock to get the collection count
    if(t_millis != 0 && os::elapsedTime() >= end_time_secs) {
      // Wait time is over
      break;
    }

    // Total collections count after the event
    unsigned int after_count;
    {
      MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
      after_count = gch->total_collections();
    }

    if(before_count != after_count) {
      // There was a collection - success
      break;
    }

    // Too many loops warning
    if(++loop_count == 0) {
      warning("wait_on_cms_lock_for_scavenge() has looped %u times", loop_count - 1);
    }
  }
}

//.........这里部分代码省略.........
    }

    // eden_end may have moved so again make sure
    // the to-space and eden don't overlap.
    to_start = MAX2(eden_end, to_start);

    // from-space
    size_t from_used = from()->used();
    if (requested_survivor_size > from_used) {
      if (from_start + requested_survivor_size >= from_start) {
        from_end = from_start + requested_survivor_size;
      }
      if (from_end > virtual_space()->high()) {
        from_end = virtual_space()->high();
      }
    }

    assert(to_start >= eden_end, "to-space should be above eden");
    if (PrintAdaptiveSizePolicy && Verbose) {
      gclog_or_tty->print_cr("    [eden_start .. eden_end): "
                    "[" PTR_FORMAT " .. " PTR_FORMAT ") " SIZE_FORMAT,
                    eden_start,
                    eden_end,
                    pointer_delta(eden_end, eden_start, sizeof(char)));
      gclog_or_tty->print_cr("    [  to_start ..   to_end): "
                    "[" PTR_FORMAT " .. " PTR_FORMAT ") " SIZE_FORMAT,
                    to_start,
                    to_end,
                    pointer_delta(  to_end,   to_start, sizeof(char)));
      gclog_or_tty->print_cr("    [from_start .. from_end): "
                    "[" PTR_FORMAT " .. " PTR_FORMAT ") " SIZE_FORMAT,
                    from_start,
                    from_end,
                    pointer_delta(from_end, from_start, sizeof(char)));
    }
  }


  guarantee((HeapWord*)from_start <= from()->bottom(),
            "from start moved to the right");
  guarantee((HeapWord*)from_end >= from()->top(),
            "from end moved into live data");
  assert(is_object_aligned((intptr_t)eden_start), "checking alignment");
  assert(is_object_aligned((intptr_t)from_start), "checking alignment");
  assert(is_object_aligned((intptr_t)to_start), "checking alignment");

  MemRegion edenMR((HeapWord*)eden_start, (HeapWord*)eden_end);
  MemRegion toMR  ((HeapWord*)to_start,   (HeapWord*)to_end);
  MemRegion fromMR((HeapWord*)from_start, (HeapWord*)from_end);

  // Let's make sure the call to initialize doesn't reset "top"!
  HeapWord* old_from_top = from()->top();

  // For PrintAdaptiveSizePolicy block  below
  size_t old_from = from()->capacity();
  size_t old_to   = to()->capacity();

  // If not clearing the spaces, do some checking to verify that
  // the spaces are already mangled.

  // Must check mangling before the spaces are reshaped.  Otherwise,
  // the bottom or end of one space may have moved into another
  // a failure of the check may not correctly indicate which space
  // is not properly mangled.
  if (ZapUnusedHeapArea) {
    HeapWord* limit = (HeapWord*) virtual_space()->high();
    eden()->check_mangled_unused_area(limit);
    from()->check_mangled_unused_area(limit);
      to()->check_mangled_unused_area(limit);
  }

  // The call to initialize NULL's the next compaction space
  eden()->initialize(edenMR,
                     SpaceDecorator::Clear,
                     SpaceDecorator::DontMangle);
  eden()->set_next_compaction_space(from());
    to()->initialize(toMR  ,
                     SpaceDecorator::Clear,
                     SpaceDecorator::DontMangle);
  from()->initialize(fromMR,
                     SpaceDecorator::DontClear,
                     SpaceDecorator::DontMangle);

  assert(from()->top() == old_from_top, "from top changed!");

  if (PrintAdaptiveSizePolicy) {
    GenCollectedHeap* gch = GenCollectedHeap::heap();
    assert(gch->kind() == CollectedHeap::GenCollectedHeap, "Sanity");

    gclog_or_tty->print("AdaptiveSizePolicy::survivor space sizes: "
                  "collection: %d "
                  "(" SIZE_FORMAT ", " SIZE_FORMAT ") -> "
                  "(" SIZE_FORMAT ", " SIZE_FORMAT ") ",
                  gch->total_collections(),
                  old_from, old_to,
                  from()->capacity(),
                  to()->capacity());
    gclog_or_tty->cr();
  }
}

HeapWord* GenCollectorPolicy::mem_allocate_work(size_t size,
                                        bool is_tlab,
                                        bool* gc_overhead_limit_was_exceeded) {
  GenCollectedHeap *gch = GenCollectedHeap::heap();

  debug_only(gch->check_for_valid_allocation_state());
  assert(gch->no_gc_in_progress(), "Allocation during gc not allowed");

  // In general gc_overhead_limit_was_exceeded should be false so
  // set it so here and reset it to true only if the gc time
  // limit is being exceeded as checked below.
  *gc_overhead_limit_was_exceeded = false;

  HeapWord* result = NULL;

  // Loop until the allocation is satisfied, or unsatisfied after GC.
  for (uint try_count = 1, gclocker_stalled_count = 0; /* return or throw */; try_count += 1) {
    HandleMark hm; // Discard any handles allocated in each iteration.

    // First allocation attempt is lock-free.
    Generation *young = gch->young_gen();
    assert(young->supports_inline_contig_alloc(),
      "Otherwise, must do alloc within heap lock");
    if (young->should_allocate(size, is_tlab)) {
      result = young->par_allocate(size, is_tlab);
      if (result != NULL) {
        assert(gch->is_in_reserved(result), "result not in heap");
        return result;
      }
    }
    uint gc_count_before;  // Read inside the Heap_lock locked region.
    {
      MutexLocker ml(Heap_lock);
      log_trace(gc, alloc)("GenCollectorPolicy::mem_allocate_work: attempting locked slow path allocation");
      // Note that only large objects get a shot at being
      // allocated in later generations.
      bool first_only = ! should_try_older_generation_allocation(size);

      result = gch->attempt_allocation(size, is_tlab, first_only);
      if (result != NULL) {
        assert(gch->is_in_reserved(result), "result not in heap");
        return result;
      }

      if (GCLocker::is_active_and_needs_gc()) {
        if (is_tlab) {
          return NULL;  // Caller will retry allocating individual object.
        }
        if (!gch->is_maximal_no_gc()) {
          // Try and expand heap to satisfy request.
          result = expand_heap_and_allocate(size, is_tlab);
          // Result could be null if we are out of space.
          if (result != NULL) {
            return result;
          }
        }

        if (gclocker_stalled_count > GCLockerRetryAllocationCount) {
          return NULL; // We didn't get to do a GC and we didn't get any memory.
        }

        // If this thread is not in a jni critical section, we stall
        // the requestor until the critical section has cleared and
        // GC allowed. When the critical section clears, a GC is
        // initiated by the last thread exiting the critical section; so
        // we retry the allocation sequence from the beginning of the loop,
        // rather than causing more, now probably unnecessary, GC attempts.
        JavaThread* jthr = JavaThread::current();
        if (!jthr->in_critical()) {
          MutexUnlocker mul(Heap_lock);
          // Wait for JNI critical section to be exited
          GCLocker::stall_until_clear();
          gclocker_stalled_count += 1;
          continue;
        } else {
          if (CheckJNICalls) {
            fatal("Possible deadlock due to allocating while"
                  " in jni critical section");
          }
          return NULL;
        }
      }

      // Read the gc count while the heap lock is held.
      gc_count_before = gch->total_collections();
    }

    VM_GenCollectForAllocation op(size, is_tlab, gc_count_before);
    VMThread::execute(&op);
    if (op.prologue_succeeded()) {
      result = op.result();
      if (op.gc_locked()) {
         assert(result == NULL, "must be NULL if gc_locked() is true");
         continue;  // Retry and/or stall as necessary.
      }

      // Allocation has failed and a collection
      // has been done.  If the gc time limit was exceeded the
      // this time, return NULL so that an out-of-memory
      // will be thrown.  Clear gc_overhead_limit_exceeded
//.........这里部分代码省略.........