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Reduce pinning by preloading superclasses #50091

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Reduce pinning by preloading superclasses #50091

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171362b
Reduce pinning by preloading superclasses
dmlloyd Sep 16, 2025
a55c3c9
Use a lookup table for constant sizes
dmlloyd Sep 17, 2025
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111 changes: 111 additions & 0 deletions ...rojects/bootstrap/runner/src/main/java/io/quarkus/bootstrap/runner/RunnerClassLoader.java
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,9 @@
import static io.quarkus.commons.classloading.ClassLoaderHelper.isInJdkPackage;

import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Enumeration;
import java.util.List;
Expand Down Expand Up @@ -146,11 +148,120 @@ private void definePackage(String pkgName, ClassLoadingResource[] resources) {
}
}

private static int u8(byte[] data, int offset) {
return Byte.toUnsignedInt(data[offset]);
}

private static int u16(byte[] data, int offset) {
return u8(data, offset) << 8 | u8(data, offset + 1);
}

private static String binaryName(byte[] data, int offset, int length) {
// maybe larger than needed
char[] ca = new char[length];
int j = 0;
for (int i = 0; i < length;) {
int lb = u8(data, offset + i);
if (lb < 0x80) {
if (lb == '/') {
lb = '.';
}
ca[j++] = (char) lb;
i++;
} else if (lb < 0xC0) {
throw new ClassFormatError("Illegal character in class name: " + lb);
} else if (lb < 0xE0) {
ca[j++] = (char) ((lb & 0x1F) << 6 | u8(data, offset + i + 1) & 0x3F);
i += 2;
} else if (lb < 0xF0) {
ca[j++] = (char) ((lb & 0x0F) << 12 | (u8(data, offset + i + 2) & 0x3F) << 6 | u8(data, offset + i + 2) & 0x3F);
i += 3;
} else {
throw new ClassFormatError("Illegal character in class name: " + lb);
}
}
return new String(ca, 0, j);
}

private static final int O_CP_COUNT = 8;
private static final int O_CP_START = 10;
private static final int O_SUPER_FROM_CP_END = 4;

private static final int CONSTANT_Utf8 = 1;
private static final int CONSTANT_Class = 7;

private static final byte[] javaLangObject = "java/lang/Object".getBytes(StandardCharsets.US_ASCII);
private static final int[] sizes = new int[] {
0, // unused
3, // [1] CONSTANT_Utf8 (special)
0, // unused
5, // [3] CONSTANT_Integer
5, // [4] CONSTANT_Float
9, // [5] CONSTANT_Long
9, // [6] CONSTANT_Double
3, // [7] CONSTANT_Class
3, // [8] CONSTANT_String
5, // [9] CONSTANT_Fieldref
5, // [10] CONSTANT_Methodref
5, // [11] CONSTANT_InterfaceMethodref
5, // [12] CONSTANT_NameAndType
0, // unused
0, // unused
0, // unused
4, // [15] CONSTANT_MethodHandle
3, // [16] CONSTANT_MethodType
5, // [17] CONSTANT_Dynamic
5, // [18] CONSTANT_InvokeDynamic
3, // [19] CONSTANT_Module
3, // [20] CONSTANT_Package
};

private Class<?> defineClass(String name, byte[] data, ClassLoadingResource resource) {
Class<?> loaded = findLoadedClass(name);
if (loaded != null) {
return loaded;
}
// scan class bytes and preload supertype(s)
try {
int cpCnt = u16(data, O_CP_COUNT);
int offs = O_CP_START;
int[] cpOffs = new int[cpCnt];
for (int i = 1; i < cpCnt; i++) {
int tag = u8(data, offs);
cpOffs[i] = offs;
if (tag == CONSTANT_Utf8) {
offs += u16(data, offs + 1);
}
offs += sizes[tag];
}
int superCp = u16(data, offs + O_SUPER_FROM_CP_END);
if (superCp != 0 && u8(data, cpOffs[superCp]) == CONSTANT_Class) {
int superCi = u16(data, cpOffs[superCp] + 1);
int superStrOffs = cpOffs[superCi];
if (superCi != 0 && u8(data, superStrOffs) == CONSTANT_Utf8) {
int superLen = u16(data, superStrOffs + 1);
// only load the class if it isn't java.lang.Object
int superStrStart = superStrOffs + 3;
if (!Arrays.equals(data, superStrStart, superStrStart + superLen, javaLangObject, 0,
javaLangObject.length)) {
String superName = binaryName(data, superStrStart, superLen);
try {
loadClass(superName);
} catch (ClassNotFoundException e) {
throw new LinkageError("Failed to load super class " + superName + " of class " + name, e);
}
loaded = findLoadedClass(name);
if (loaded != null) {
return loaded;
}
}
}
}
} catch (ArrayIndexOutOfBoundsException e) {
ClassFormatError error = new ClassFormatError("Failed to load class " + name);
error.initCause(e);
throw error;
}
try {
return defineClass(name, data, 0, data.length, resource.getProtectionDomain());
} catch (LinkageError e) {
Expand Down