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[GR-51330] Support per-thread suspend/resume.
PullRequest: graal/16838
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substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/ThreadSuspendSupport.java
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| /* | ||
| * Copyright (c) 2024, 2024, Oracle and/or its affiliates. All rights reserved. | ||
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| * | ||
| * This code is free software; you can redistribute it and/or modify it | ||
| * under the terms of the GNU General Public License version 2 only, as | ||
| * published by the Free Software Foundation. Oracle designates this | ||
| * particular file as subject to the "Classpath" exception as provided | ||
| * by Oracle in the LICENSE file that accompanied this code. | ||
| * | ||
| * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| * version 2 for more details (a copy is included in the LICENSE file that | ||
| * accompanied this code). | ||
| * | ||
| * You should have received a copy of the GNU General Public License version | ||
| * 2 along with this work; if not, write to the Free Software Foundation, | ||
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| * | ||
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| * or visit www.oracle.com if you need additional information or have any | ||
| * questions. | ||
| */ | ||
| package com.oracle.svm.core.thread; | ||
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| import org.graalvm.nativeimage.IsolateThread; | ||
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| import com.oracle.svm.core.heap.VMOperationInfos; | ||
| import com.oracle.svm.core.thread.VMThreads.StatusSupport; | ||
| import com.oracle.svm.core.util.VMError; | ||
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| /** | ||
| * Support for suspending and resuming threads. | ||
| * <p> | ||
| * Once a thread is suspended, we guarantee that it won't execute any Java code until it is resumed | ||
| * explicitly. However, suspended threads may still execute native code (including uninterruptible | ||
| * AOT-compiled Native Image code). Such threads will get blocked when they try to change their | ||
| * thread status to {@link StatusSupport#STATUS_IN_JAVA} (forced safepoint slow-path). | ||
| * <p> | ||
| * After a safepoint, suspended threads remain in {@link StatusSupport#STATUS_IN_SAFEPOINT}, even | ||
| * though there is no global safepoint at the moment. The suspends and resumes are counted. A thread | ||
| * needs to be resumed the same number of times it was suspended to continue again. | ||
| * <p> | ||
| * Note that there are races possible, for example: | ||
| * <ul> | ||
| * <li>Thread A starts detaching.</li> | ||
| * <li>Thread B suspends thread A.</li> | ||
| * <li>Thread A exits without ever being suspended because it is already in uninterruptible code and | ||
| * does not enter the safepoint slowpath anymore.</li> | ||
| * </ul> | ||
| * | ||
| * or | ||
| * | ||
| * <ul> | ||
| * <li>Thread A wants to suspend thread B and requests a VM operation.</li> | ||
| * <li>Thread B exits before the VM operation starts.</li> | ||
| * </ul> | ||
| */ | ||
| public final class ThreadSuspendSupport { | ||
| private ThreadSuspendSupport() { | ||
| } | ||
|
|
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| /** | ||
| * Suspends a thread. If the thread was already suspended, only the suspension counter will be | ||
| * incremented. | ||
| */ | ||
| public static void suspend(Thread thread) { | ||
| VMError.guarantee(!thread.isVirtual(), "must not be called for virtual threads"); | ||
| ThreadSuspendOperation op = new ThreadSuspendOperation(thread); | ||
| op.enqueue(); | ||
| } | ||
|
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| /** | ||
| * Decrements the suspension counter of the thread and resumes the thread if the counter reaches | ||
| * 0. | ||
| */ | ||
| public static void resume(Thread thread) { | ||
| VMError.guarantee(!thread.isVirtual(), "must not be called for virtual threads"); | ||
| ThreadResumeOperation op = new ThreadResumeOperation(thread); | ||
| op.enqueue(); | ||
| } | ||
|
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| private static void suspend(IsolateThread isolateThread) { | ||
| VMThreads.guaranteeOwnsThreadMutex("Must own the THREAD_MUTEX to prevent races."); | ||
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| int newValue = Safepoint.suspendedTL.get(isolateThread) + 1; | ||
| VMError.guarantee(newValue > 0, "Too many thread suspends."); | ||
| Safepoint.suspendedTL.set(isolateThread, newValue); | ||
| } | ||
|
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| private static void resume(IsolateThread isolateThread) { | ||
| VMThreads.guaranteeOwnsThreadMutex("Must own the THREAD_MUTEX to prevent races."); | ||
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| int newValue = Safepoint.suspendedTL.get(isolateThread) - 1; | ||
| VMError.guarantee(newValue >= 0, "Only a suspended thread can be resumed."); | ||
| Safepoint.suspendedTL.set(isolateThread, newValue); | ||
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| if (newValue == 0) { | ||
| Safepoint.COND_SUSPEND.broadcast(); | ||
| } | ||
| } | ||
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| private static class ThreadSuspendOperation extends JavaVMOperation { | ||
| private final Thread thread; | ||
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| ThreadSuspendOperation(Thread thread) { | ||
| super(VMOperationInfos.get(ThreadSuspendOperation.class, "Thread Suspend", SystemEffect.SAFEPOINT)); | ||
| this.thread = thread; | ||
| } | ||
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| @Override | ||
| protected void operate() { | ||
| IsolateThread isolateThread = PlatformThreads.getIsolateThread(thread); | ||
| if (isolateThread.isNonNull()) { | ||
| ThreadSuspendSupport.suspend(isolateThread); | ||
| } | ||
| } | ||
| } | ||
|
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| private static class ThreadResumeOperation extends JavaVMOperation { | ||
| private final Thread thread; | ||
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| ThreadResumeOperation(Thread thread) { | ||
| super(VMOperationInfos.get(ThreadResumeOperation.class, "Thread Resume", SystemEffect.SAFEPOINT)); | ||
| this.thread = thread; | ||
| } | ||
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| @Override | ||
| protected void operate() { | ||
| IsolateThread isolateThread = PlatformThreads.getIsolateThread(thread); | ||
| if (isolateThread.isNonNull()) { | ||
| ThreadSuspendSupport.resume(isolateThread); | ||
| } | ||
| } | ||
| } | ||
| } |
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