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Truffle is a multi-language framework for executing dynamic languages that achieves high performance when combined with Graal.
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/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * person obtaining a copy of this software, associated documentation and/or
 * data (collectively the "Software"), free of charge and under any and all
 * copyright rights in the Software, and any and all patent rights owned or
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 * unmodified Software as contributed to or provided by such licensor, or (ii)
 * the Larger Works (as defined below), to deal in both
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 * (a) the Software, and
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 * (b) any piece of software and/or hardware listed in the lrgrwrks.txt file if
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package com.oracle.truffle.api.debug;

import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
import com.oracle.truffle.api.debug.Breakpoint.SessionList;
import com.oracle.truffle.api.debug.DebuggerSession.ThreadSuspension;
import com.oracle.truffle.api.dsl.Cached;
import com.oracle.truffle.api.dsl.Specialization;
import com.oracle.truffle.api.nodes.ExplodeLoop;
import com.oracle.truffle.api.nodes.Node;

/**
 * This node sets thread-local enabled suspension flag. It uses {@link DebuggerSession}'s
 * {@link ThreadLocal} field, which is cached in 10 threads for fast access.
 */
abstract class SetThreadSuspensionEnabledNode extends Node {

    static final int CACHE_LIMIT = 10;

    public final void execute(boolean suspensionEnabled, SessionList sessions) {
        execute(suspensionEnabled, sessions, Thread.currentThread().getId());
    }

    protected abstract void execute(boolean suspensionEnabled, SessionList sessions, long threadId);

    @Specialization(guards = {"sessions.next == null", "threadId == currentThreadId"}, limit = "CACHE_LIMIT")
    protected void executeCached(boolean suspensionEnabled,
                    @SuppressWarnings("unused") SessionList sessions,
                    @SuppressWarnings("unused") long threadId,
                    @SuppressWarnings("unused") @Cached("currentThreadId()") long currentThreadId,
                    @Cached("getThreadSuspension(sessions)") ThreadSuspension threadSuspension) {
        threadSuspension.enabled = suspensionEnabled;
    }

    @ExplodeLoop
    @Specialization(replaces = "executeCached")
    protected void executeGeneric(boolean suspensionEnabled,
                    SessionList sessions,
                    @SuppressWarnings("unused") long threadId) {
        SessionList current = sessions;
        while (current != null) {
            current.session.setThreadSuspendEnabled(suspensionEnabled);
            current = current.next;
        }

    }

    static long currentThreadId() {
        return Thread.currentThread().getId();
    }

    @TruffleBoundary
    protected ThreadSuspension getThreadSuspension(SessionList sessions) {
        assert sessions.next == null;
        ThreadSuspension threadSuspension = new ThreadSuspension(true);
        sessions.session.threadSuspensions.set(threadSuspension);
        return threadSuspension;
    }

}