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 import jdk.internal.access.JavaLangAccess;
29 import jdk.internal.access.SharedSecrets;
30
31
32 // Signalling operations on native threads
33 //
34 // On some operating systems (e.g., Linux), closing a channel while another
35 // thread is blocked in an I/O operation upon that channel does not cause that
36 // thread to be released. This class provides access to the native threads
37 // upon which Java threads are built, and defines a simple signal mechanism
38 // that can be used to release a native thread from a blocking I/O operation.
39 // On systems that do not require this type of signalling, the current() method
40 // always returns -1 and the signal(long) method has no effect.
41
42 public class NativeThread {
43 private static final JavaLangAccess JLA = SharedSecrets.getJavaLangAccess();
44 private static final long VIRTUAL_THREAD_ID = -1L;
45
46 private final Thread thread;
47 private final long tid;
48
49 private NativeThread(Thread thread, long tid) {
50 this.thread = thread;
51 this.tid = tid;
52 }
53
54 Thread thread() {
55 return thread;
56 }
57
58 /**
59 * Return a NativeThread for the current thread.
60 */
61 public static NativeThread current() {
62 Thread t = Thread.currentThread();
63 if (t.isVirtual()) {
64 // return new object for now
65 return new NativeThread(t, VIRTUAL_THREAD_ID);
66 } else {
67 NativeThread nt = JLA.nativeThread(t);
68 if (nt == null) {
69 nt = new NativeThread(t, current0());
70 JLA.setNativeThread(nt);
71 }
72 return nt;
73 }
74 }
75
76 /**
77 * Return a NativeThread for the current platform thread. Returns null if called
78 * from a virtual thread.
79 */
80 public static NativeThread currentNativeThread() {
81 Thread t = Thread.currentThread();
82 if (t.isVirtual()) {
83 return null;
84 } else {
85 NativeThread nt = JLA.nativeThread(t);
86 if (nt == null) {
87 nt = new NativeThread(t, current0());
88 JLA.setNativeThread(nt);
89 }
90 return nt;
91 }
92 }
93
94 /**
95 * Return true if the given NativeThread is a platform thread.
96 */
97 public static boolean isNativeThread(NativeThread nt) {
98 return nt != null && nt.tid != VIRTUAL_THREAD_ID;
99 }
100
101 /**
102 * Return true if the given NativeThread is a virtual thread.
103 */
104 public static boolean isVirtualThread(NativeThread nt) {
105 return nt != null && nt.tid == VIRTUAL_THREAD_ID;
106 }
107
108 /**
109 * Signals this native thread.
110 * @throws UnsupportedOperationException if virtual thread
111 */
112 public void signal() {
113 if (tid == VIRTUAL_THREAD_ID)
114 throw new UnsupportedOperationException();
115 signal0(tid);
116 }
117
118 /**
119 * Return true if the operating system supports pending signals. If a signal is sent
120 * to a thread but cannot be delivered immediately then it will be delivered when the
121 * thread is in the appropriate state.
122 */
123 static boolean supportPendingSignals() {
124 return supportPendingSignals0();
125 }
126
127 private static native boolean supportPendingSignals0();
128
129 // Returns an opaque token representing the native thread underlying the
130 // invoking Java thread. On systems that do not require signalling, this
131 // method always returns 0.
132 //
133 private static native long current0();
134
135 // Signals the given native thread so as to release it from a blocking I/O
136 // operation. On systems that do not require signalling, this method has
137 // no effect.
138 //
139 private static native void signal0(long tid);
140
141 private static native void init();
142
143 static {
144 IOUtil.load();
145 init();
146 }
147
148 }