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 
  40 import jdk.internal.misc.Strands;
  41 
  42 public class NativeThread {
  43     private static final long FIBER_ID = -1L;
  44 
  45     /**
  46      * Returns a token representing the current thread or -1 if called in the
  47      * context of a Fiber.
  48      */
  49     public static long current() {
  50         Object s = Strands.currentStrand();
  51         if (s instanceof Fiber) {
  52             return FIBER_ID;
  53         } else {
  54             return current0();
  55         }
  56     }
  57 
  58     /**
  59      * Returns a token representing the current kernel thread
  60      */
  61     static long currentKernelThread() {
  62         return current0();
  63     }
  64 
  65     /**
  66      * Signals the given thread.
  67      *
  68      * @throws IllegalArgumentException if tid is not a token to a kernel thread
  69      */
  70     public static void signal(long tid) {
  71         if (tid == 0 || tid == FIBER_ID)
  72             throw new IllegalArgumentException();
  73         signal0(tid);
  74     }
  75 
  76     /**
  77      * Returns true if the token presents a fiber rather than a thread
  78      */
  79     static boolean isFiber(long tid) {
  80         return (tid == FIBER_ID);
  81     }
  82 
  83     /**
  84      * Returns true if the token presents a kernel thread
  85      */
  86     static boolean isKernelThread(long tid) {
  87         return (tid != 0 && tid != FIBER_ID);
  88     }
  89 
  90     // Returns an opaque token representing the native thread underlying the
  91     // invoking Java thread.  On systems that do not require signalling, this
  92     // method always returns 0.
  93     //
  94     private static native long current0();
  95 
  96     // Signals the given native thread so as to release it from a blocking I/O
  97     // operation.  On systems that do not require signalling, this method has
  98     // no effect.
  99     //
 100     private static native void signal0(long tid);
 101 
 102     private static native void init();
 103 
 104     static {
 105         IOUtil.load();
 106         init();
 107     }
 108 
 109 }