diff -r 7d5a4a48e876 src/java.base/share/classes/java/lang/System.java

--- a/src/java.base/share/classes/java/lang/System.java	Wed Mar 27 14:40:36 2019 -0700

+++ b/src/java.base/share/classes/java/lang/System.java	Wed Apr 03 09:46:50 2019 +0100

@@ -2172,6 +2172,12 @@

             public void blockedOn(Interruptible b) {

                 Thread.blockedOn(b);

             }

+            public void setNativeTid(long tid) {

+                Thread.setNativeTid(tid);

+            }

+            public long nativeTid() {

+                return Thread.nativeTid();

+            }

             public void registerShutdownHook(int slot, boolean registerShutdownInProgress, Runnable hook) {

                 Shutdown.add(slot, registerShutdownInProgress, hook);

             }

diff -r 7d5a4a48e876 src/java.base/share/classes/java/lang/Thread.java

--- a/src/java.base/share/classes/java/lang/Thread.java	Wed Mar 27 14:40:36 2019 -0700

+++ b/src/java.base/share/classes/java/lang/Thread.java	Wed Apr 03 09:46:50 2019 +0100

@@ -241,6 +241,18 @@

     }

     /**

+     * Native thread id, cached here for use for threads are blocked in I/O

+     * operations.

+     */

+    private long nativeTid;

+    static void setNativeTid(long tid) {

+        Thread.currentThread().nativeTid = tid;

+    }

+    static long nativeTid() {

+        return Thread.currentThread().nativeTid;

+    }

+

+    /**

      * The minimum priority that a thread can have.

      */

     public static final int MIN_PRIORITY = 1;

diff -r 7d5a4a48e876 src/java.base/share/classes/jdk/internal/access/JavaLangAccess.java

--- a/src/java.base/share/classes/jdk/internal/access/JavaLangAccess.java	Wed Mar 27 14:40:36 2019 -0700

+++ b/src/java.base/share/classes/jdk/internal/access/JavaLangAccess.java	Wed Apr 03 09:46:50 2019 +0100

@@ -107,6 +107,16 @@

     void blockedOn(Interruptible b);

     /**

+     * Set the current thread's native ID

+     */

+    void setNativeTid(long tid);

+

+    /**

+     * Returns the current thread's native ID

+     */

+    long nativeTid();

+

+    /**

      * Registers a shutdown hook.

      *

      * It is expected that this method with registerShutdownInProgress=true

diff -r 7d5a4a48e876 src/java.base/unix/classes/sun/nio/ch/NativeThread.java

--- a/src/java.base/unix/classes/sun/nio/ch/NativeThread.java	Wed Mar 27 14:40:36 2019 -0700

+++ b/src/java.base/unix/classes/sun/nio/ch/NativeThread.java	Wed Apr 03 09:46:50 2019 +0100

@@ -25,7 +25,6 @@

 package sun.nio.ch;

-

 // Signalling operations on native threads

 //

 // On some operating systems (e.g., Linux), closing a channel while another

@@ -33,23 +32,35 @@

 // thread to be released.  This class provides access to the native threads

 // upon which Java threads are built, and defines a simple signal mechanism

 // that can be used to release a native thread from a blocking I/O operation.

-// On systems that do not require this type of signalling, the current() method

-// always returns -1 and the signal(long) method has no effect.

+import jdk.internal.access.JavaLangAccess;

+import jdk.internal.access.SharedSecrets;

 public class NativeThread {

+    private static final JavaLangAccess JLA = SharedSecrets.getJavaLangAccess();

-    // Returns an opaque token representing the native thread underlying the

-    // invoking Java thread.  On systems that do not require signalling, this

-    // method always returns -1.

-    //

-    public static native long current();

+    /**

+     * Returns the current thread's ID.

+     */

+    public static long current() {

+        long tid = JLA.nativeTid();

+        if (tid == 0) {

+            tid = current0();

+            JLA.setNativeTid(tid);

+        }

+        return tid;

+    }

-    // Signals the given native thread so as to release it from a blocking I/O

-    // operation.  On systems that do not require signalling, this method has

-    // no effect.

-    //

-    public static native void signal(long nt);

+    /**

+     * Signals the given thread.

+     */

+    public static void signal(long tid) {

+        signal0(tid);

+    }

+

+    private static native long current0();

+

+    private static native void signal0(long tid);

     private static native void init();

diff -r 7d5a4a48e876 src/java.base/unix/native/libnio/ch/NativeThread.c

--- a/src/java.base/unix/native/libnio/ch/NativeThread.c	Wed Mar 27 14:40:36 2019 -0700

+++ b/src/java.base/unix/native/libnio/ch/NativeThread.c	Wed Apr 03 09:46:50 2019 +0100

@@ -77,7 +77,7 @@

 }

 JNIEXPORT jlong JNICALL

-Java_sun_nio_ch_NativeThread_current(JNIEnv *env, jclass cl)

+Java_sun_nio_ch_NativeThread_current0(JNIEnv *env, jclass cl)

 {

 #ifdef __solaris__

     return (jlong)thr_self();

@@ -87,7 +87,7 @@

 }

 JNIEXPORT void JNICALL

-Java_sun_nio_ch_NativeThread_signal(JNIEnv *env, jclass cl, jlong thread)

+Java_sun_nio_ch_NativeThread_signal0(JNIEnv *env, jclass cl, jlong thread)

 {

     int ret;

 #ifdef __solaris__