8278241: Implement JVM SpinPause on linux-aarch64

Reviewed-by: aph, phh

src/hotspot/cpu/aarch64/stubGenerator_aarch64.cpp

@@ -6397,6 +6397,18 @@ class StubGenerator: public StubCodeGenerator {
     return start;
   }
 
+  // Support for spin waits.
+  address generate_spin_wait() {
+    __ align(CodeEntryAlignment);
+    StubCodeMark mark(this, "StubRoutines", "spin_wait");
+    address start = __ pc();
+
+    __ spin_wait();
+    __ ret(lr);
+
+    return start;
+  }
+
 #ifdef LINUX
 
   // ARMv8.1 LSE versions of the atomic stubs used by Atomic::PlatformXX.
@@ -7715,6 +7727,8 @@ class StubGenerator: public StubCodeGenerator {
       StubRoutines::_updateBytesAdler32 = generate_updateBytesAdler32();
     }
 
+    StubRoutines::aarch64::_spin_wait = generate_spin_wait();
+
 #ifdef LINUX
 
     generate_atomic_entry_points();

src/hotspot/cpu/aarch64/stubRoutines_aarch64.cpp

@@ -57,6 +57,10 @@ address StubRoutines::aarch64::_string_indexof_linear_uu = NULL;
 address StubRoutines::aarch64::_string_indexof_linear_ul = NULL;
 address StubRoutines::aarch64::_large_byte_array_inflate = NULL;
 address StubRoutines::aarch64::_method_entry_barrier = NULL;
+
+static void empty_spin_wait() { }
+address StubRoutines::aarch64::_spin_wait = CAST_FROM_FN_PTR(address, empty_spin_wait);
+
 bool StubRoutines::aarch64::_completed = false;
 
 /**

src/hotspot/cpu/aarch64/stubRoutines_aarch64.hpp

@@ -72,6 +72,8 @@ class aarch64 {
 
   static address _method_entry_barrier;
 
+  static address _spin_wait;
+
   static bool _completed;
 
  public:
@@ -177,6 +179,10 @@ class aarch64 {
     return _method_entry_barrier;
   }
 
+  static address spin_wait() {
+    return _spin_wait;
+  }
+
   static bool complete() {
     return _completed;
   }

src/hotspot/os_cpu/linux_aarch64/os_linux_aarch64.cpp

@@ -382,7 +382,20 @@ int os::extra_bang_size_in_bytes() {
 
 extern "C" {
   int SpinPause() {
-    return 0;
+    using spin_wait_func_ptr_t = void (*)();
+    spin_wait_func_ptr_t func = CAST_TO_FN_PTR(spin_wait_func_ptr_t, StubRoutines::aarch64::spin_wait());
+    assert(func != nullptr, "StubRoutines::aarch64::spin_wait must not be null.");
+    (*func)();
+    // If StubRoutines::aarch64::spin_wait consists of only a RET,
+    // SpinPause can be considered as implemented. There will be a sequence
+    // of instructions for:
+    // - call of SpinPause
+    // - load of StubRoutines::aarch64::spin_wait stub pointer
+    // - indirect call of the stub
+    // - return from the stub
+    // - return from SpinPause
+    // So '1' always is returned.
+    return 1;
   }
 
   void _Copy_conjoint_jshorts_atomic(const jshort* from, jshort* to, size_t count) {

test/hotspot/jtreg/runtime/Thread/TestSpinPause.java

@@ -0,0 +1,87 @@
+/*
+ * Copyright Amazon.com Inc. 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.
+ *
+ * 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.
+ */
+
+/**
+ * @test TestSpinPause
+ * @summary JVM runtime can use SpinPause function for synchronized statements.
+ *          Check different implementations of JVM SpinPause don't crash JVM.
+ * @bug 8278241
+ * @library /test/lib
+ *
+ * @requires os.arch=="aarch64"
+ *
+ * @run main/othervm TestSpinPause
+ * @run main/othervm -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=none TestSpinPause
+ * @run main/othervm -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=nop TestSpinPause
+ * @run main/othervm -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=isb TestSpinPause
+ * @run main/othervm -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=yield TestSpinPause
+ * @run main/othervm -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=nop -XX:OnSpinWaitInstCount=10 TestSpinPause
+ * @run main/othervm -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=isb -XX:OnSpinWaitInstCount=3 TestSpinPause
+ * @run main/othervm -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=yield -XX:OnSpinWaitInstCount=3 TestSpinPause
+ * @run main/othervm -Xint TestSpinPause
+ * @run main/othervm -Xint -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=none TestSpinPause
+ * @run main/othervm -Xint -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=nop TestSpinPause
+ * @run main/othervm -Xint -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=isb TestSpinPause
+ * @run main/othervm -Xint -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=yield TestSpinPause
+ * @run main/othervm -Xint -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=nop -XX:OnSpinWaitInstCount=10 TestSpinPause
+ * @run main/othervm -Xint -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=isb -XX:OnSpinWaitInstCount=3 TestSpinPause
+ * @run main/othervm -Xint -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=yield -XX:OnSpinWaitInstCount=3 TestSpinPause
+ * @run main/othervm -Xcomp TestSpinPause
+ * @run main/othervm -Xcomp -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=none TestSpinPause
+ * @run main/othervm -Xcomp -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=nop TestSpinPause
+ * @run main/othervm -Xcomp -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=isb TestSpinPause
+ * @run main/othervm -Xcomp -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=yield TestSpinPause
+ * @run main/othervm -Xcomp -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=nop -XX:OnSpinWaitInstCount=10 TestSpinPause
+ * @run main/othervm -Xcomp -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=isb -XX:OnSpinWaitInstCount=3 TestSpinPause
+ * @run main/othervm -Xcomp -XX:+UnlockDiagnosticVMOptions -XX:OnSpinWaitInst=yield -XX:OnSpinWaitInstCount=3 TestSpinPause
+ */
+
+public class TestSpinPause {
+    private Integer[] valueHolder;
+
+    private TestSpinPause () {
+        valueHolder = new Integer[] {Integer.valueOf(101)};
+    }
+
+    private void getSet() {
+        final int iterCount = 100;
+        for (int i = 0; i < iterCount; ++i) {
+           synchronized (valueHolder) {
+               Integer v = valueHolder[0];
+               valueHolder[0] = Integer.reverse(v);
+           }
+        }
+    }
+
+    public static void main(String[] args) throws Exception {
+        TestSpinPause test = new TestSpinPause();
+        Thread t1 = new Thread(test::getSet);
+        Thread t2 = new Thread(test::getSet);
+        t1.start();
+        t2.start();
+        t1.join();
+        t2.join();
+        System.out.println("Done: " + test.valueHolder[0]);
+    }
+}
+