1 /*
2 * Copyright (c) 2002, 2025, 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 * Signals the given native thread.
57 *
58 * @throws IllegalArgumentException if tid is not a token to a native thread
59 */
60 public static void signal(long tid) {
61 if (tid == 0 || tid == VIRTUAL_THREAD_ID)
62 throw new IllegalArgumentException();
63 signal0(tid);
64 }
65
66 /**
67 * Returns true the tid is the id of a native thread.
68 */
69 static boolean isNativeThread(long tid) {
70 return (tid != 0 && tid != VIRTUAL_THREAD_ID);
71 }
72
73 /**
74 * Returns true if tid is -1L.
75 * @see #current()
76 */
77 static boolean isVirtualThread(long tid) {
78 return (tid == VIRTUAL_THREAD_ID);
79 }
80
81 /**
82 * Return true if the operating system supports pending signals. If a signal is sent
83 * to a thread but cannot be delivered immediately then it will be delivered when the
84 * thread is in the appropriate state.
85 */
86 static boolean supportPendingSignals() {
87 return supportPendingSignals0();
88 }
89
90 private static native boolean supportPendingSignals0();
91
92 // Returns an opaque token representing the native thread underlying the
93 // invoking Java thread. On systems that do not require signalling, this
94 // method always returns 0.
95 //
96 private static native long current0();
97
98 // Signals the given native thread so as to release it from a blocking I/O
99 // operation. On systems that do not require signalling, this method has
100 // no effect.
101 //
102 private static native void signal0(long tid);
103
104 private static native void init();
105
106 static {
107 IOUtil.load();
108 init();
109 }
110
111 }