Not call java methods from within JNI init code to prevent class loading deadlocks.

Motivation:

We used NetUtil.isIpV4StackPreferred() when loading JNI code which tries to load NetworkInterface in its static initializer. Unfortunally a lock on the NetworkInterface class init may be already hold somewhere else which may cause a loader deadlock.

Modifications:

Add a new Socket.initialize() method that will be called when init the library and pass everything needed to the JNI level so we not need to call back to java.

Result:

Fixes [#7458].

transport-native-epoll/src/main/c/netty_unix_socket.c

@@ -40,9 +40,7 @@ static jmethodID datagramSocketAddrMethodId = NULL;
 static jmethodID inetSocketAddrMethodId = NULL;
 static jmethodID peerCredentialsMethodId = NULL;
 static jclass inetSocketAddressClass = NULL;
-static jclass netUtilClass = NULL;
-static jmethodID netUtilClassIpv4PreferredMethodId = NULL;
-static int socketType;
+static int socketType = AF_INET;
 static const char* ip4prefix = "::ffff:";
 static const unsigned char wildcardAddress[] = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
 static const unsigned char ipv4MappedWildcardAddress[] = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00 };
@@ -155,30 +153,26 @@ static jbyteArray createInetSocketAddressArray(JNIEnv* env, const struct sockadd
     return bArray;
 }
 
-static int socket_type(JNIEnv* env) {
-    jboolean ipv4Preferred = (*env)->CallStaticBooleanMethod(env, netUtilClass, netUtilClassIpv4PreferredMethodId);
-
+static void netty_unix_socket_initialize(JNIEnv* env, jclass clazz, jboolean ipv4Preferred) {
     if (ipv4Preferred) {
         // User asked to use ipv4 explicitly.
-        return AF_INET;
-    }
-    int fd = socket(AF_INET6, SOCK_STREAM | SOCK_NONBLOCK, 0);
-    if (fd == -1) {
-        if (errno == EAFNOSUPPORT) {
-            return AF_INET;
-        }
-        return AF_INET6;
+        socketType = AF_INET;
     } else {
-        // Explicitly try to bind to ::1 to ensure IPV6 can really be used.
-        // See https://github.com/netty/netty/issues/7021.
-        struct sockaddr_in6 addr;
-        memset(&addr, 0, sizeof(addr));
-        addr.sin6_family = AF_INET6;
-        addr.sin6_addr.s6_addr[15] = 1; /* [::1]:0 */
-        int res = bind(fd, (struct sockaddr *)&addr, sizeof(addr));
+        int fd = socket(AF_INET6, SOCK_STREAM | SOCK_NONBLOCK, 0);
+        if (fd == -1) {
+            socketType = errno == EAFNOSUPPORT ? AF_INET : AF_INET6;
+        } else {
+            // Explicitly try to bind to ::1 to ensure IPV6 can really be used.
+            // See https://github.com/netty/netty/issues/7021.
+            struct sockaddr_in6 addr;
+            memset(&addr, 0, sizeof(addr));
+            addr.sin6_family = AF_INET6;
+            addr.sin6_addr.s6_addr[15] = 1; /* [::1]:0 */
+            int res = bind(fd, (struct sockaddr *)&addr, sizeof(addr));
 
-        close(fd);
-        return res == 0 ? AF_INET6 : AF_INET;
+            close(fd);
+            socketType = res == 0 ? AF_INET6 : AF_INET;
+        }
     }
 }
 
@@ -746,7 +740,8 @@ static const JNINativeMethod fixed_method_table[] = {
   { "getSoLinger", "(I)I", (void *) netty_unix_socket_getSoLinger },
   { "getSoError", "(I)I", (void *) netty_unix_socket_getSoError },
   { "getTcpDeferAccept", "(I)I", (void *) netty_unix_socket_getTcpDeferAccept },
-  { "isTcpQuickAck", "(I)I", (void *) netty_unix_socket_isTcpQuickAck }
+  { "isTcpQuickAck", "(I)I", (void *) netty_unix_socket_isTcpQuickAck },
+  { "initialize", "(Z)V", (void *) netty_unix_socket_initialize }
 };
 static const jint fixed_method_table_size = sizeof(fixed_method_table) / sizeof(fixed_method_table[0]);
 
@@ -835,26 +830,6 @@ jint netty_unix_socket_JNI_OnLoad(JNIEnv* env, const char* packagePrefix) {
         netty_unix_errors_throwRuntimeException(env, "failed to get method ID: InetSocketAddress.<init>(String, int)");
         return JNI_ERR;
     }
-    nettyClassName = netty_unix_util_prepend(packagePrefix, "io/netty/util/NetUtil");
-    jclass localNetUtilClass = (*env)->FindClass(env, nettyClassName);
-    free(nettyClassName);
-    nettyClassName = NULL;
-    if (localNetUtilClass == NULL) {
-        // pending exception...
-        return JNI_ERR;
-    }
-    netUtilClass = (jclass) (*env)->NewGlobalRef(env, localNetUtilClass);
-    if (netUtilClass == NULL) {
-        // out-of-memory!
-        netty_unix_errors_throwOutOfMemoryError(env);
-        return JNI_ERR;
-    }
-    netUtilClassIpv4PreferredMethodId = (*env)->GetStaticMethodID(env, netUtilClass, "isIpV4StackPreferred", "()Z" );
-    if (netUtilClassIpv4PreferredMethodId == NULL) {
-        // position method was not found.. something is wrong so bail out
-        netty_unix_errors_throwRuntimeException(env, "failed to get method ID: NetUild.isIpV4StackPreferred()");
-        return JNI_ERR;
-    }
     
     nettyClassName = netty_unix_util_prepend(packagePrefix, "io/netty/channel/unix/PeerCredentials");
     jclass localPeerCredsClass = (*env)->FindClass(env, nettyClassName);
@@ -896,7 +871,6 @@ jint netty_unix_socket_JNI_OnLoad(JNIEnv* env, const char* packagePrefix) {
     }
     free(mem);
 
-    socketType = socket_type(env);
     return JNI_VERSION_1_6;
 }
 
@@ -909,10 +883,6 @@ void netty_unix_socket_JNI_OnUnLoad(JNIEnv* env) {
         (*env)->DeleteGlobalRef(env, inetSocketAddressClass);
         inetSocketAddressClass = NULL;
     }
-    if (netUtilClass != NULL) {
-        (*env)->DeleteGlobalRef(env, netUtilClass);
-        netUtilClass = NULL;
-    }
     if (peerCredentialsClass != NULL) {
         (*env)->DeleteGlobalRef(env, peerCredentialsClass);
         peerCredentialsClass = NULL;

transport-native-epoll/src/main/java/io/netty/channel/epoll/Native.java

@@ -17,11 +17,12 @@ package io.netty.channel.epoll;
 
 import io.netty.channel.DefaultFileRegion;
 import io.netty.channel.unix.Errors.NativeIoException;
+import io.netty.channel.unix.NativeInetAddress;
+import io.netty.channel.unix.Socket;
 import io.netty.util.internal.NativeLibraryLoader;
 import io.netty.util.internal.PlatformDependent;
 import io.netty.util.internal.SystemPropertyUtil;
 import io.netty.channel.unix.FileDescriptor;
-import io.netty.channel.unix.NativeInetAddress;
 import io.netty.util.internal.ThrowableUtil;
 import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
@@ -67,6 +68,7 @@ public final class Native {
             // The library was not previously loaded, load it now.
             loadNativeLibrary();
         }
+        Socket.initialize();
     }
 
     // EventLoop operations and constants

transport-native-epoll/src/main/java/io/netty/channel/unix/Socket.java

@@ -17,6 +17,7 @@ package io.netty.channel.unix;
 
 import io.netty.channel.ChannelException;
 import io.netty.util.CharsetUtil;
+import io.netty.util.NetUtil;
 
 import java.io.IOException;
 import java.net.Inet6Address;
@@ -26,6 +27,7 @@ import java.net.PortUnreachableException;
 import java.net.SocketAddress;
 import java.nio.ByteBuffer;
 import java.nio.channels.ClosedChannelException;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 import static io.netty.channel.unix.Errors.ERRNO_EAGAIN_NEGATIVE;
 import static io.netty.channel.unix.Errors.ERROR_ECONNREFUSED_NEGATIVE;
@@ -381,6 +383,14 @@ public final class Socket extends FileDescriptor {
                 '}';
     }
 
+    private static final AtomicBoolean INITIALIZED = new AtomicBoolean();
+
+    public static void initialize() {
+        if (INITIALIZED.compareAndSet(false, true)) {
+            initialize(NetUtil.isIpV4StackPreferred());
+        }
+    }
+
     public static Socket newSocketStream() {
         int res = newSocketStreamFd();
         if (res < 0) {
@@ -453,4 +463,5 @@ public final class Socket extends FileDescriptor {
     private static native void setSoLinger(int fd, int soLinger) throws IOException;
     private static native void setTcpDeferAccept(int fd, int deferAccept) throws IOException;
     private static native void setTcpQuickAck(int fd, int quickAck) throws IOException;
+    private static native void initialize(boolean ipv4Preferred);
 }