jdk-sandbox: comparison hotspot/src/share/vm/runtime/jniHandles.hpp

equal deleted inserted replaced

-:5bc48f22b149
+:a46a6c4d1dd9
 /*
-* Copyright (c) 1998, 2014, Oracle and/or its affiliates. All rights reserved.
+* Copyright (c) 1998, 2017, 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.
 private:
 static JNIHandleBlock* _global_handles;             // First global handle block
 static JNIHandleBlock* _weak_global_handles;        // First weak global handle block
 static oop _deleted_handle;                         // Sentinel marking deleted handles
+inline static bool is_jweak(jobject handle);
+inline static oop& jobject_ref(jobject handle); // NOT jweak!
+inline static oop& jweak_ref(jobject handle);
+template<bool external_guard> inline static oop guard_value(oop value);
+template<bool external_guard> inline static oop resolve_impl(jobject handle);
+template<bool external_guard> static oop resolve_jweak(jweak handle);
 public:
+// Low tag bit in jobject used to distinguish a jweak.  jweak is
+// type equivalent to jobject, but there are places where we need to
+// be able to distinguish jweak values from other jobjects, and
+// is_weak_global_handle is unsuitable for performance reasons.  To
+// provide such a test we add weak_tag_value to the (aligned) byte
+// address designated by the jobject to produce the corresponding
+// jweak.  Accessing the value of a jobject must account for it
+// being a possibly offset jweak.
+static const uintptr_t weak_tag_size = 1;
+static const uintptr_t weak_tag_alignment = (1u << weak_tag_size);
+static const uintptr_t weak_tag_mask = weak_tag_alignment - 1;
+static const int weak_tag_value = 1;
 // Resolve handle into oop
 inline static oop resolve(jobject handle);
 // Resolve externally provided handle into oop with some guards
 inline static oop resolve_external_guard(jobject handle);
 // Resolve handle into oop, result guaranteed not to be null
 static bool any_contains(jobject handle);     // Does any block currently in use contain handle
 static void print_statistics();
 #endif
 };
+inline bool JNIHandles::is_jweak(jobject handle) {
+STATIC_ASSERT(weak_tag_size == 1);
+STATIC_ASSERT(weak_tag_value == 1);
+return (reinterpret_cast<uintptr_t>(handle) & weak_tag_mask) != 0;
+}
+inline oop& JNIHandles::jobject_ref(jobject handle) {
+assert(!is_jweak(handle), "precondition");
+return *reinterpret_cast<oop*>(handle);
+}
+inline oop& JNIHandles::jweak_ref(jobject handle) {
+assert(is_jweak(handle), "precondition");
+char* ptr = reinterpret_cast<char*>(handle) - weak_tag_value;
+return *reinterpret_cast<oop*>(ptr);
+}
+// external_guard is true if called from resolve_external_guard.
+// Treat deleted (and possibly zapped) as NULL for external_guard,
+// else as (asserted) error.
+template<bool external_guard>
+inline oop JNIHandles::guard_value(oop value) {
+if (!external_guard) {
+assert(value != badJNIHandle, "Pointing to zapped jni handle area");
+assert(value != deleted_handle(), "Used a deleted global handle");
+} else if ((value == badJNIHandle) || (value == deleted_handle())) {
+value = NULL;
+}
+return value;
+}
+// external_guard is true if called from resolve_external_guard.
+template<bool external_guard>
+inline oop JNIHandles::resolve_impl(jobject handle) {
+assert(handle != NULL, "precondition");
+oop result;
+if (is_jweak(handle)) {       // Unlikely
+result = resolve_jweak<external_guard>(handle);
+} else {
+result = jobject_ref(handle);
+// Construction of jobjects canonicalize a null value into a null
+// jobject, so for non-jweak the pointee should never be null.
+assert(external_guard || result != NULL,
+"Invalid value read from jni handle");
+result = guard_value<external_guard>(result);
+}
+return result;
+}
 inline oop JNIHandles::resolve(jobject handle) {
-oop result = (handle == NULL ? (oop)NULL : *(oop*)handle);
+oop result = NULL;
-assert(result != NULL || (handle == NULL || !CheckJNICalls || is_weak_global_handle(handle)), "Invalid value read from jni handle");
+if (handle != NULL) {
-assert(result != badJNIHandle, "Pointing to zapped jni handle area");
+result = resolve_impl<false /* external_guard */ >(handle);
-return result;
+}
-};
+return result;
+}
+// Resolve some erroneous cases to NULL, rather than treating them as
+// possibly unchecked errors.  In particular, deleted handles are
+// treated as NULL (though a deleted and later reallocated handle
+// isn't detected).
 inline oop JNIHandles::resolve_external_guard(jobject handle) {
-if (handle == NULL) return NULL;
+oop result = NULL;
-oop result = *(oop*)handle;
+if (handle != NULL) {
-if (result == NULL || result == badJNIHandle) return NULL;
+result = resolve_impl<true /* external_guard */ >(handle);
-return result;
+}
-};
+return result;
+}
 inline oop JNIHandles::resolve_non_null(jobject handle) {
 assert(handle != NULL, "JNI handle should not be null");
-oop result = *(oop*)handle;
+oop result = resolve_impl<false /* external_guard */ >(handle);
-assert(result != NULL, "Invalid value read from jni handle");
+assert(result != NULL, "NULL read from jni handle");
-assert(result != badJNIHandle, "Pointing to zapped jni handle area");
+return result;
-// Don't let that private _deleted_handle object escape into the wild.
+}
-assert(result != deleted_handle(), "Used a deleted global handle.");
-return result;
-};
 inline void JNIHandles::destroy_local(jobject handle) {
 if (handle != NULL) {
-*((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
+jobject_ref(handle) = deleted_handle();
 }
 }
 #endif // SHARE_VM_RUNTIME_JNIHANDLES_HPP

changeset 44406	a46a6c4d1dd9
parent 44093	e22e0d071bf9
child 46703	f152b500376e