HeapWord* PermGen::mem_allocate_in_gen(size_t size, Generation* gen) {

  MutexLocker ml(Heap_lock);

  GCCause::Cause next_cause = GCCause::_permanent_generation_full;

  GCCause::Cause prev_cause = GCCause::_no_gc;

  for (;;) {

    HeapWord* obj = gen->allocate(size, false);

    if (obj != NULL) {

      return obj;

    }

    if (gen->capacity() < _capacity_expansion_limit ||

        prev_cause != GCCause::_no_gc) {

      obj = gen->expand_and_allocate(size, false);

    }

    if (obj == NULL && prev_cause != GCCause::_last_ditch_collection) {

      if (GC_locker::is_active_and_needs_gc()) {

        // 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

          GC_locker::stall_until_clear();

          continue;

        } else {

          if (CheckJNICalls) {

            fatal("Possible deadlock due to allocating while"

                  " in jni critical section");

          }

          return NULL;

        }

      }

      // Read the GC count while holding the Heap_lock

      unsigned int gc_count_before      = SharedHeap::heap()->total_collections();

      unsigned int full_gc_count_before = SharedHeap::heap()->total_full_collections();

      {

        MutexUnlocker mu(Heap_lock);  // give up heap lock, execute gets it back

        VM_GenCollectForPermanentAllocation op(size, gc_count_before, full_gc_count_before,

                                               next_cause);

        VMThread::execute(&op);

        if (!op.prologue_succeeded() || op.gc_locked()) {

          assert(op.result() == NULL, "must be NULL if gc_locked() is true");

          continue;  // retry and/or stall as necessary

        }

        obj = op.result();

        assert(obj == NULL || SharedHeap::heap()->is_in_reserved(obj),

               "result not in heap");

        if (obj != NULL) {

          return obj;

        }

      }

      prev_cause = next_cause;

      next_cause = GCCause::_last_ditch_collection;

    } else {

      return obj;

    }

  }

}

  return mem_allocate_in_gen(size, _gen);