In j.u.ServerLoader, use the platform classloader after the module system is initialized but before the VM initialization is completed. Don't use the system classloader to find resources if the loader is null when finding service provider.

There are two issues uncovered when FileSystemProvider.loadInstalledProviders() is called early during system startup before the VM is initialized. The VM is considered in booted state after System.initPhase3() completes.

1) In nextProviderClass(), when the loader is null, ClassLoader.getSystemResources() is called to find the service. The result can include service providers that can only be loaded by the system class loader, e.g. in JAR files on the -classpath. That can cause failure when the null classloader is trying to load the provider class.

This issue is addressed by changing to call 'BootLoader.findResources(fullName)' instead, if the 'loader' is null.

2) When trying to load installed FileSystemProvider during early start up before the VM is booted, it fails to find the 'jar' provider. That's because the boot loader (a.k.a. the null classloader) is used by ServiceLoader, which tries to only use the code in java.base at the time. The ZipFileSystemProvider and JarFileSystemProvider are in jdk.zipfs module.

The JavaHome is trying to use the JarFileSystem during initPhase3, which is after system module initialization. During that phase, it can use the platform classloader to load the installed provider, which would able to find the ZipFileSystemProvider and JarFileSystemProvider.

These issues are found by hermetic Java testing, however I think these are not specific to hermetic Java.

Author: jianglizhou

src/java.base/share/classes/java/util/ServiceLoader.java

@@ -516,8 +516,13 @@ private ServiceLoader(Class<?> caller, Class<S> svc, ClassLoader cl) {
                 fail(svc, "not accessible to " + callerModule + " during VM init");
             }
 
-            // restricted to boot loader during startup
-            cl = null;
+            // If the module system is not initialized yet, restrict to boot
+            // loader during startup.
+            if (!VM.isModuleSystemInited()) {
+                cl = null;
+            } else {
+                cl = ClassLoader.getPlatformClassLoader();
+            }
         }
 
         this.service = svc;
@@ -1186,7 +1191,10 @@ private Class<?> nextProviderClass() {
                 try {
                     String fullName = PREFIX + service.getName();
                     if (loader == null) {
-                        configs = ClassLoader.getSystemResources(fullName);
+                        // Find the resources using the boot loader. Don't use
+                        // the system class loader here since we will load the
+                        // provider class using the null loader below.
+                        configs = BootLoader.findResources(fullName);
                     } else if (loader == ClassLoaders.platformClassLoader()) {
                         // The platform classloader doesn't have a class path,
                         // but the boot loader might.