8295803: Console should be usable in jshell and other environments

Reviewed-by: jlaskey, alanb

src/java.base/share/classes/java/io/Console.java

@@ -25,10 +25,13 @@
 
 package java.io;
 
+import java.security.AccessController;
+import java.security.PrivilegedAction;
 import java.util.*;
 import java.nio.charset.Charset;
 import jdk.internal.access.JavaIOAccess;
 import jdk.internal.access.SharedSecrets;
+import jdk.internal.io.JdkConsoleProvider;
 import jdk.internal.util.StaticProperty;
 import sun.nio.cs.StreamDecoder;
 import sun.nio.cs.StreamEncoder;
@@ -45,7 +48,7 @@ import sun.security.action.GetPropertyAction;
  * output streams then its console will exist and will typically be
  * connected to the keyboard and display from which the virtual machine
  * was launched.  If the virtual machine is started automatically, for
- * example by a background job scheduler, then it will typically not
+ * example by a background job scheduler, then it may not
  * have a console.
  * <p>
  * If this virtual machine has a console then it is represented by a
@@ -93,7 +96,7 @@ import sun.security.action.GetPropertyAction;
  * @since   1.6
  */
 
-public final class Console implements Flushable
+public class Console implements Flushable
 {
    /**
     * Retrieves the unique {@link java.io.PrintWriter PrintWriter} object
@@ -592,25 +595,43 @@ public final class Console implements Flushable
 
         CHARSET = cs;
 
+        cons = instantiateConsole(istty);
+
         // Set up JavaIOAccess in SharedSecrets
         SharedSecrets.setJavaIOAccess(new JavaIOAccess() {
             public Console console() {
-                if (istty) {
-                    if (cons == null)
-                        cons = new Console();
-                    return cons;
-                }
-                return null;
-            }
-
-            public Charset charset() {
-                return CHARSET;
+                return cons;
             }
         });
     }
-    private static Console cons;
+
+    @SuppressWarnings("removal")
+    private static Console instantiateConsole(boolean istty) {
+        try {
+            // Try loading providers
+            PrivilegedAction<Console> pa = () -> {
+                var consModName = System.getProperty("jdk.console",
+                        JdkConsoleProvider.DEFAULT_PROVIDER_MODULE_NAME);
+                return ServiceLoader.load(ModuleLayer.boot(), JdkConsoleProvider.class).stream()
+                        .map(ServiceLoader.Provider::get)
+                        .filter(jcp -> consModName.equals(jcp.getClass().getModule().getName()))
+                        .map(jcp -> jcp.console(istty, CHARSET))
+                        .filter(Objects::nonNull)
+                        .findAny()
+                        .map(jc -> (Console) new ProxyingConsole(jc))
+                        .orElse(istty ? new Console() : null);
+            };
+            return AccessController.doPrivileged(pa);
+        } catch (ServiceConfigurationError ignore) {
+            // default to built-in Console
+            return istty ? new Console() : null;
+        }
+    }
+
+    private static final Console cons;
     private static native boolean istty();
-    private Console() {
+
+    Console() {
         readLock = new Object();
         writeLock = new Object();
         out = StreamEncoder.forOutputStreamWriter(

src/java.base/share/classes/java/io/PrintWriter.java

@@ -208,6 +208,15 @@ public class PrintWriter extends Writer {
              false);
     }
 
+    /* Package private constructor, using the specified lock
+     * for synchronization.
+     */
+    PrintWriter(Writer out, Object lock) {
+        super(lock);
+        this.out = out;
+        this.autoFlush = false;
+    }
+
     /* Private constructor */
     private PrintWriter(Charset charset, File file)
         throws FileNotFoundException

src/java.base/share/classes/java/io/ProxyingConsole.java

@@ -0,0 +1,198 @@
+/*
+ * Copyright (c) 2022, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.io;
+
+import java.nio.charset.Charset;
+import jdk.internal.io.JdkConsole;
+
+/**
+ * Console implementation for internal use. Custom Console delegate may be
+ * provided with jdk.internal.io.JdkConsoleProvider.
+ */
+final class ProxyingConsole extends Console {
+    private final JdkConsole delegate;
+    private final Object readLock;
+    private final Object writeLock;
+    private final Reader reader;
+    private final PrintWriter printWriter;
+
+    ProxyingConsole(JdkConsole delegate) {
+        this.delegate = delegate;
+        readLock = new Object();
+        writeLock = new Object();
+        reader = new WrappingReader(delegate.reader(), readLock);
+        printWriter = new WrappingWriter(delegate.writer(), writeLock);
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public PrintWriter writer() {
+        return printWriter;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public Reader reader() {
+        return reader;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public Console format(String fmt, Object ... args) {
+        synchronized (writeLock) {
+            delegate.format(fmt, args);
+        }
+        return this;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public Console printf(String format, Object ... args) {
+        synchronized (writeLock) {
+            delegate.printf(format, args);
+        }
+        return this;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public String readLine(String fmt, Object ... args) {
+        synchronized (writeLock) {
+            synchronized (readLock) {
+                return delegate.readLine(fmt, args);
+            }
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public String readLine() {
+        synchronized (readLock) {
+            return delegate.readLine();
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public char[] readPassword(String fmt, Object ... args) {
+        synchronized (writeLock) {
+            synchronized (readLock) {
+                return delegate.readPassword(fmt, args);
+            }
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public char[] readPassword() {
+        synchronized (readLock) {
+            return delegate.readPassword();
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void flush() {
+        delegate.flush();
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public Charset charset() {
+        return delegate.charset();
+    }
+
+    private static class WrappingReader extends Reader {
+        private final Reader r;
+        private final Object lock;
+
+        WrappingReader(Reader r, Object lock) {
+            super(lock);
+            this.r = r;
+            this.lock = lock;
+        }
+
+        @Override
+        public int read(char[] cbuf, int off, int len) throws IOException {
+            synchronized (lock) {
+                return r.read(cbuf, off, len);
+            }
+        }
+
+        @Override
+        public void close() {
+            // no-op, per Console's spec
+        }
+    }
+
+    private static class WrappingWriter extends PrintWriter {
+        private final PrintWriter pw;
+        private final Object lock;
+
+        public WrappingWriter(PrintWriter pw, Object lock) {
+            super(pw, lock);
+            this.pw = pw;
+            this.lock = lock;
+        }
+
+        @Override
+        public void write(char[] cbuf, int off, int len) {
+            synchronized (lock) {
+                pw.write(cbuf, off, len);
+            }
+        }
+
+        @Override
+        public void flush() {
+            pw.flush();
+        }
+
+        @Override
+        public void close() {
+            // no-op, per Console's spec
+        }
+    }
+}