1 /*
 2  * Copyright (c) 2018, 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 #ifndef SHARE_GC_SHARED_GCTHREADLOCALDATA_HPP
25 #define SHARE_GC_SHARED_GCTHREADLOCALDATA_HPP
26 
27 #include "utilities/globalDefinitions.hpp"
28 
29 // Thread local data area for GC-specific information. Each GC
30 // is free to decide the internal structure and contents of this
31 // area. It is represented as a 64-bit aligned opaque blob to
32 // avoid circular dependencies between Thread and all GCs. For
33 // the same reason, the size of the data area is hard coded to
34 // provide enough space for all current GCs. Adjust the size if
35 // needed, but avoid making it excessively large as it adds to
36 // the memory overhead of creating a thread.
37 //
38 // Use Thread::gc_data<T>() to access the data, where T is the
39 // GC-specific type describing the structure of the data. GCs
40 // should consider placing frequently accessed fields first in
41 // T, so that field offsets relative to Thread are small, which
42 // often allows for a more compact instruction encoding.
43 typedef uint64_t GCThreadLocalData[18]; // 144 bytes
44 
45 #endif // SHARE_GC_SHARED_GCTHREADLOCALDATA_HPP