1 /*
  2  * Copyright (c) 2002, 2022, 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 the id of the current native thread if the platform can signal
 44      * native threads, 0 if the platform can not signal native threads, or
 45      * -1L if the current thread is a virtual thread.
 46      */
 47     public static long current() {
 48         if (Thread.currentThread().isVirtual()) {
 49             return VIRTUAL_THREAD_ID;
 50         } else {
 51             return current0();
 52         }
 53     }
 54 
 55     /**
 56      * Returns the id of the current native thread if the platform can signal
 57      * native threads, 0 if the platform can not signal native threads.
 58      */
 59     static long currentNativeThread() {
 60         return current0();
 61     }
 62 
 63     /**
 64      * Signals the given native thread.
 65      *
 66      * @throws IllegalArgumentException if tid is not a token to a native thread
 67      */
 68     public static void signal(long tid) {
 69         if (tid == 0 || tid == VIRTUAL_THREAD_ID)
 70             throw new IllegalArgumentException();
 71         signal0(tid);
 72     }
 73 
 74     /**
 75      * Returns true the tid is the id of a native thread.
 76      */
 77     static boolean isNativeThread(long tid) {
 78         return (tid != 0 && tid != VIRTUAL_THREAD_ID);
 79     }
 80 
 81     /**
 82      * Returns true if tid is -1L.
 83      * @see #current()
 84      */
 85     static boolean isVirtualThread(long tid) {
 86         return (tid == VIRTUAL_THREAD_ID);
 87     }
 88 
 89     // Returns an opaque token representing the native thread underlying the
 90     // invoking Java thread.  On systems that do not require signalling, this
 91     // method always returns 0.
 92     //
 93     private static native long current0();
 94 
 95     // Signals the given native thread so as to release it from a blocking I/O
 96     // operation.  On systems that do not require signalling, this method has
 97     // no effect.
 98     //
 99     private static native void signal0(long tid);
100 
101     private static native void init();
102 
103     static {
104         IOUtil.load();
105         init();
106     }
107 
108 }