1 /*
  2  * Copyright (c) 2002, 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.  Oracle designates this
  8  * particular file as subject to the "Classpath" exception as provided
  9  * by Oracle in the LICENSE file that accompanied this code.
 10  *
 11  * This code is distributed in the hope that it will be useful, but WITHOUT
 12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 14  * version 2 for more details (a copy is included in the LICENSE file that
 15  * accompanied this code).
 16  *
 17  * You should have received a copy of the GNU General Public License version
 18  * 2 along with this work; if not, write to the Free Software Foundation,
 19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 20  *
 21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 22  * or visit www.oracle.com if you need additional information or have any
 23  * questions.
 24  */
 25 
 26 package sun.nio.ch;
 27 
 28 
 29 // Signalling operations on native threads
 30 //
 31 // On some operating systems (e.g., Linux), closing a channel while another
 32 // thread is blocked in an I/O operation upon that channel does not cause that
 33 // thread to be released.  This class provides access to the native threads
 34 // upon which Java threads are built, and defines a simple signal mechanism
 35 // that can be used to release a native thread from a blocking I/O operation.
 36 // On systems that do not require this type of signalling, the current() method
 37 // always returns -1 and the signal(long) method has no effect.
 38 
 39 public class NativeThread {
 40     private static final long VIRTUAL_THREAD_ID = -1L;
 41 
 42     /**
 43      * Returns a token representing the current thread or -1 if called in the
 44      * context of a virtual thread
 45      */
 46     public static long current() {
 47         if (Thread.currentThread().isVirtual()) {
 48             return VIRTUAL_THREAD_ID;
 49         } else {
 50             return current0();
 51         }
 52     }
 53 
 54     /**
 55      * Returns a token representing the current kernel thread
 56      */
 57     static long currentKernelThread() {
 58         return current0();
 59     }
 60 
 61     /**
 62      * Signals the given thread.
 63      *
 64      * @throws IllegalArgumentException if tid is not a token to a kernel thread
 65      */
 66     public static void signal(long tid) {
 67         if (tid == 0 || tid == VIRTUAL_THREAD_ID)
 68             throw new IllegalArgumentException();
 69         signal0(tid);
 70     }
 71 
 72     /**
 73      * Returns true if the token presents a virtual thread
 74      */
 75     static boolean isVirtualThread(long tid) {
 76         return (tid == VIRTUAL_THREAD_ID);
 77     }
 78 
 79     /**
 80      * Returns true if the token presents a kernel thread
 81      */
 82     static boolean isKernelThread(long tid) {
 83         return (tid != 0 && tid != VIRTUAL_THREAD_ID);
 84     }
 85 
 86     // Returns an opaque token representing the native thread underlying the
 87     // invoking Java thread.  On systems that do not require signalling, this
 88     // method always returns 0.
 89     //
 90     private static native long current0();
 91 
 92     // Signals the given native thread so as to release it from a blocking I/O
 93     // operation.  On systems that do not require signalling, this method has
 94     // no effect.
 95     //
 96     private static native void signal0(long tid);
 97 
 98     private static native void init();
 99 
100     static {
101         IOUtil.load();
102         init();
103     }
104 
105 }