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 java.util.concurrent.locks.LockSupport;
29 import jdk.internal.access.JavaLangAccess;
30 import jdk.internal.access.SharedSecrets;
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
45 private NativeThread() { }
46
47 /**
48 * Returns the Thread to signal the current thread.
49 *
50 * The first use of this method on a platform thread will capture the thread's
51 * native thread ID.
52 */
53 public static Thread threadToSignal() {
54 Thread t = Thread.currentThread();
55 if (!t.isVirtual() && JLA.nativeThreadID(t) == 0) {
56 JLA.setThreadNativeID(current0());
57 }
58 return t;
59 }
60
61 /**
62 * Signals the given thread. For a platform thread it sends a signal to the thread.
63 * For a virtual thread it just unparks it.
64 * @throws IllegalStateException if the thread is a platform thread that hasn't set its native ID
65 */
66 public static void signal(Thread thread) {
67 if (thread.isVirtual()) {
68 LockSupport.unpark(thread);
69 } else {
70 long id = JLA.nativeThreadID(thread);
71 if (id == 0)
72 throw new IllegalStateException("Native thread ID not set");
73 signal0(id);
74 }
75 }
76
77 /**
78 * Return true if the operating system supports pending signals. If a signal is sent
79 * to a thread but cannot be delivered immediately then it will be delivered when the
80 * thread is in the appropriate state.
81 */
82 static boolean supportPendingSignals() {
83 return supportPendingSignals0();
84 }
85
86 private static native boolean supportPendingSignals0();
87
88 // Returns an opaque token representing the native thread underlying the
89 // invoking Java thread. On systems that do not require signalling, this
90 // method always returns 0.
91 //
92 private static native long current0();
93
94 // Signals the given native thread so as to release it from a blocking I/O
95 // operation. On systems that do not require signalling, this method has
96 // no effect.
97 //
98 private static native void signal0(long tid);
99
100 private static native void init();
101
102 static {
103 IOUtil.load();
104 init();
105 }
106
107 }