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@tommyettinger
Created April 26, 2023 04:17
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-XstartOnFirstThread (Magic)
/*
* Copyright 2020 damios
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at:
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
// package copy.me.into.your.lwjgl3.project;
import org.lwjgl.system.macosx.LibC;
import java.io.BufferedReader;
import java.io.File;
import java.io.InputStreamReader;
import java.lang.management.ManagementFactory;
import java.util.ArrayList;
/**
* Adds some utilities to ensure that the JVM was started with the
* {@code -XstartOnFirstThread} argument, which is required on macOS for LWJGL 3
* to function. Also helps on Windows when users have names with characters from
* outside the Latin alphabet, a common cause of startup crashes.
*
* @author damios
* @see <a href="https://jvm-gaming.org/t/starting-jvm-on-mac-with-xstartonfirstthread-programmatically/57547">Based on this java-gaming.org post by kappa</a>
*/
public class StartOnFirstThreadHelper {
private static final String JVM_RESTARTED_ARG = "jvmIsRestarted";
private StartOnFirstThreadHelper() {
throw new UnsupportedOperationException();
}
/**
* Starts a new JVM if the application was started on macOS without the
* {@code -XstartOnFirstThread} argument. This also includes some code for
* Windows, for the case where the user's home directory includes certain
* non-Latin-alphabet characters (without this code, most LWJGL3 apps fail
* immediately for those users). Returns whether a new JVM was started and
* thus no code should be executed.
* <p>
* <u>Usage:</u>
*
* <pre><code>
* public static void main(String... args) {
* if (StartOnFirstThreadHelper.startNewJvmIfRequired()) return; // don't execute any code
* // after this is the actual main method code
* }
* </code></pre>
*
* @param redirectOutput
* whether the output of the new JVM should be rerouted to the
* old JVM, so it can be accessed in the same place; keeps the
* old JVM running if enabled
* @return whether a new JVM was started and thus no code should be executed
* in this one
*/
public static boolean startNewJvmIfRequired(boolean redirectOutput) {
String osName = System.getProperty("os.name").toLowerCase();
if (!osName.contains("mac")) {
if (osName.contains("windows")) {
// Here, we are trying to work around an issue with how LWJGL3 loads its extracted .dll files.
// By default, LWJGL3 extracts to the directory specified by "java.io.tmpdir", which is usually the user's home.
// If the user's name has non-ASCII (or some non-alphanumeric) characters in it, that would fail.
// By extracting to the relevant "ProgramData" folder, which is usually "C:\ProgramData", we avoid this.
System.setProperty("java.io.tmpdir", System.getenv("ProgramData") + "/libGDX-temp");
}
return false;
}
long pid = LibC.getpid();
// check whether -XstartOnFirstThread is enabled
if ("1".equals(System.getenv("JAVA_STARTED_ON_FIRST_THREAD_" + pid))) {
return false;
}
// check whether the JVM was previously restarted
// avoids looping, but most certainly leads to a crash
if ("true".equals(System.getProperty(JVM_RESTARTED_ARG))) {
System.err.println(
"There was a problem evaluating whether the JVM was started with the -XstartOnFirstThread argument.");
return false;
}
// Restart the JVM with -XstartOnFirstThread
ArrayList<String> jvmArgs = new ArrayList<String>();
String separator = System.getProperty("file.separator");
// TODO Java 9: ProcessHandle.current().info().command();
String javaExecPath = System.getProperty("java.home") + separator
+ "bin" + separator + "java";
if (!(new File(javaExecPath)).exists()) {
System.err.println(
"A Java installation could not be found. If you are distributing this app with a bundled JRE, be sure to set the -XstartOnFirstThread argument manually!");
return false;
}
jvmArgs.add(javaExecPath);
jvmArgs.add("-XstartOnFirstThread");
jvmArgs.add("-D" + JVM_RESTARTED_ARG + "=true");
jvmArgs.addAll(ManagementFactory.getRuntimeMXBean().getInputArguments());
jvmArgs.add("-cp");
jvmArgs.add(System.getProperty("java.class.path"));
String mainClass = System.getenv("JAVA_MAIN_CLASS_" + pid);
if (mainClass == null) {
StackTraceElement[] trace = Thread.currentThread().getStackTrace();
if (trace.length > 0) {
mainClass = trace[trace.length - 1].getClassName();
} else {
System.err.println("The main class could not be determined.");
return false;
}
}
jvmArgs.add(mainClass);
try {
if (!redirectOutput) {
ProcessBuilder processBuilder = new ProcessBuilder(jvmArgs);
processBuilder.start();
} else {
Process process = (new ProcessBuilder(jvmArgs))
.redirectErrorStream(true).start();
BufferedReader processOutput = new BufferedReader(
new InputStreamReader(process.getInputStream()));
String line;
while ((line = processOutput.readLine()) != null) {
System.out.println(line);
}
process.waitFor();
}
} catch (Exception e) {
System.err.println("There was a problem restarting the JVM");
e.printStackTrace();
}
return true;
}
/**
* Starts a new JVM if the application was started on macOS without the
* {@code -XstartOnFirstThread} argument. Returns whether a new JVM was
* started and thus no code should be executed. Redirects the output of the
* new JVM to the old one.
* <p>
* <u>Usage:</u>
*
* <pre>
* public static void main(String... args) {
* if (StartOnFirstThreadHelper.startNewJvmIfRequired()) return; // don't execute any code
* // the actual main method code
* }
* </pre>
*
* @return whether a new JVM was started and thus no code should be executed
* in this one
*/
public static boolean startNewJvmIfRequired() {
return startNewJvmIfRequired(true);
}
}
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