C++ Generation::should_allocate方法代码示例

HeapWord* GenCollectorPolicy::expand_heap_and_allocate(size_t size,
                                                       bool   is_tlab) {
  GenCollectedHeap *gch = GenCollectedHeap::heap();
  HeapWord* result = NULL;
  Generation *old = gch->old_gen();
  if (old->should_allocate(size, is_tlab)) {
    result = old->expand_and_allocate(size, is_tlab);
  }
  if (result == NULL) {
    Generation *young = gch->young_gen();
    if (young->should_allocate(size, is_tlab)) {
      result = young->expand_and_allocate(size, is_tlab);
    }
  }
  assert(result == NULL || gch->is_in_reserved(result), "result not in heap");
  return result;
}

HeapWord* GenCollectorPolicy::expand_heap_and_allocate(size_t size,
                                                       bool   is_tlab) {
  GenCollectedHeap *gch = GenCollectedHeap::heap();
  HeapWord* result = NULL;
  for (int i = number_of_generations() - 1; i >= 0 && result == NULL; i--) {
    Generation *gen = gch->get_gen(i);
    if (gen->should_allocate(size, is_tlab)) {
      result = gen->expand_and_allocate(size, is_tlab);
    }
  }
  assert(result == NULL || gch->is_in_reserved(result), "result not in heap");
  return result;
}

HeapWord* TwoGenerationCollectorPolicy::satisfy_failed_allocation(size_t size,
                                                                  bool   is_large_noref,
                                                                  bool   is_tlab,
                                                                  bool*  notify_ref_lock) {
  GenCollectedHeap *gch = GenCollectedHeap::heap();
  GCCauseSetter x(gch, GCCause::_allocation_failure);
  HeapWord* result = NULL;
  
  // The gc_prologues have not executed yet.  The value
  // for incremental_collection_will_fail() is the remanent 
  // of the last collection.
  if (!gch->incremental_collection_will_fail()) {
    // Do an incremental collection.
    gch->do_collection(false            /* full */,
                       false            /* clear_all_soft_refs */,
                       size             /* size */,
                       is_large_noref   /* is_large_noref */,
                       is_tlab          /* is_tlab */,
                       number_of_generations() - 1 /* max_level */,
                       notify_ref_lock  /* notify_ref_lock */);
  } else {
    // The incremental_collection_will_fail flag is set if the
    // next incremental collection will not succeed (e.g., the
    // DefNewGeneration didn't think it had space to promote all
    // its objects). However, that last incremental collection
    // continued, allowing all older generations to collect (and
    // perhaps change the state of the flag).
    // 
    // If we reach here, we know that an incremental collection of
    // all generations left us in the state where incremental collections
    // will fail, so we just try allocating the requested space. 
    // If the allocation fails everywhere, force a full collection.
    // We're probably very close to being out of memory, so forcing many
    // collections now probably won't help.
    if (PrintGC && Verbose) {
      gclog_or_tty->print_cr("TwoGenerationCollectorPolicy::satisfy_failed_allocation:"
                    " attempting allocation anywhere before full collection");
    }
    result = gch->attempt_allocation(size, 
                                     is_large_noref, 
                                     is_tlab, 
                                     false /* first_only */);
    if (result != NULL) {
      assert(gch->is_in(result), "result not in heap");
      return result;
    }

    // Allocation request hasn't yet been met; try a full collection.
    gch->do_collection(true             /* full */, 
                       false            /* clear_all_soft_refs */, 
                       size             /* size */, 
                       is_large_noref   /* is_large_noref */,
                       is_tlab          /* is_tlab */,
                       number_of_generations() - 1 /* max_level */, 
                       notify_ref_lock  /* notify_ref_lock */);
  }
  
  result = gch->attempt_allocation(size, is_large_noref, is_tlab, false /*first_only*/);
  
  if (result != NULL) {
    assert(gch->is_in(result), "result not in heap");
    return result;
  }
  
  // OK, collection failed, try expansion.
  for (int i = number_of_generations() - 1 ; i>= 0; i--) {
    Generation *gen = gch->get_gen(i);
    if (gen->should_allocate(size, is_large_noref, is_tlab)) {
      result = gen->expand_and_allocate(size, is_large_noref, is_tlab);
      if (result != NULL) {
        assert(gch->is_in(result), "result not in heap");
        return result;
      }
    }
  }
  
  // If we reach this point, we're really out of memory. Try every trick
  // we can to reclaim memory. Force collection of soft references. Force
  // a complete compaction of the heap. Any additional methods for finding
  // free memory should be here, especially if they are expensive. If this
  // attempt fails, an OOM exception will be thrown.
  {
    IntFlagSetting flag_change(MarkSweepAlwaysCompactCount, 1); // Make sure the heap is fully compacted

    gch->do_collection(true             /* full */,
                       true             /* clear_all_soft_refs */,
                       size             /* size */,
                       is_large_noref   /* is_large_noref */,
                       is_tlab          /* is_tlab */,
                       number_of_generations() - 1 /* max_level */,
                       notify_ref_lock  /* notify_ref_lock */);
  }

  result = gch->attempt_allocation(size, is_large_noref, is_tlab, false /* first_only */);
  if (result != NULL) {
    assert(gch->is_in(result), "result not in heap");
    return result;
  }
  
  // What else?  We might try synchronous finalization later.  If the total
//.........这里部分代码省略.........

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.........