/* * Copyright 1998-2010 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, * CA 95054 USA or visit www.sun.com if you need additional information or * have any questions. * */ class JNIHandleBlock; // Interface for creating and resolving local/global JNI handles class JNIHandles : AllStatic { friend class VMStructs; 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 public: // 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 inline static oop resolve_non_null(jobject handle); // Local handles static jobject make_local(oop obj); static jobject make_local(JNIEnv* env, oop obj); // Fast version when env is known static jobject make_local(Thread* thread, oop obj); // Even faster version when current thread is known inline static void destroy_local(jobject handle); // Global handles static jobject make_global(Handle obj); static void destroy_global(jobject handle); // Weak global handles static jobject make_weak_global(Handle obj); static void destroy_weak_global(jobject handle); // jmethodID handling (as Weak global handles). // Because the useful life-span of a jmethodID cannot be determined, once created they are // never reclaimed. The methods to which they refer, however, can be GC'ed away if the class // is unloaded or if the method is made obsolete or deleted -- in these cases, the jmethodID // refers to NULL (as is the case for any weak reference). static jmethodID make_jmethod_id(methodHandle mh); static void destroy_jmethod_id(jmethodID mid); // Use resolve_jmethod_id() in situations where the caller is expected // to provide a valid jmethodID; the only sanity checks are in asserts; // result guaranteed not to be NULL. inline static methodOop resolve_jmethod_id(jmethodID mid); // Use checked_resolve_jmethod_id() in situations where the caller // should provide a valid jmethodID, but might not. NULL is returned // when the jmethodID does not refer to a valid method. inline static methodOop checked_resolve_jmethod_id(jmethodID mid); static void change_method_associated_with_jmethod_id(jmethodID jmid, methodHandle mh); // Sentinel marking deleted handles in block. Note that we cannot store NULL as // the sentinel, since clearing weak global JNI refs are done by storing NULL in // the handle. The handle may not be reused before destroy_weak_global is called. static oop deleted_handle() { return _deleted_handle; } // Initialization static void initialize(); // Debugging static void print_on(outputStream* st); static void print() { print_on(tty); } static void verify(); static bool is_local_handle(Thread* thread, jobject handle); static bool is_frame_handle(JavaThread* thr, jobject obj); static bool is_global_handle(jobject handle); static bool is_weak_global_handle(jobject handle); static long global_handle_memory_usage(); static long weak_global_handle_memory_usage(); // Garbage collection support(global handles only, local handles are traversed from thread) // Traversal of regular global handles static void oops_do(OopClosure* f); // Traversal of weak global handles. Unreachable oops are cleared. static void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f); }; // JNI handle blocks holding local/global JNI handles class JNIHandleBlock : public CHeapObj { friend class VMStructs; private: enum SomeConstants { block_size_in_oops = 32 // Number of handles per handle block }; oop _handles[block_size_in_oops]; // The handles int _top; // Index of next unused handle JNIHandleBlock* _next; // Link to next block // The following instance variables are only used by the first block in a chain. // Having two types of blocks complicates the code and the space overhead in negligble. JNIHandleBlock* _last; // Last block in use JNIHandleBlock* _pop_frame_link; // Block to restore on PopLocalFrame call oop* _free_list; // Handle free list int _allocate_before_rebuild; // Number of blocks to allocate before rebuilding free list #ifndef PRODUCT JNIHandleBlock* _block_list_link; // Link for list below static JNIHandleBlock* _block_list; // List of all allocated blocks (for debugging only) #endif static JNIHandleBlock* _block_free_list; // Free list of currently unused blocks static int _blocks_allocated; // For debugging/printing // Fill block with bad_handle values void zap(); // No more handles in the both the current and following blocks void clear() { _top = 0; } // Free list computation void rebuild_free_list(); public: // Handle allocation jobject allocate_handle(oop obj); // Block allocation and block free list management static JNIHandleBlock* allocate_block(Thread* thread = NULL); static void release_block(JNIHandleBlock* block, Thread* thread = NULL); // JNI PushLocalFrame/PopLocalFrame support JNIHandleBlock* pop_frame_link() const { return _pop_frame_link; } void set_pop_frame_link(JNIHandleBlock* block) { _pop_frame_link = block; } // Stub generator support static int top_offset_in_bytes() { return offset_of(JNIHandleBlock, _top); } // Garbage collection support // Traversal of regular handles void oops_do(OopClosure* f); // Traversal of weak handles. Unreachable oops are cleared. void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f); // Debugging bool chain_contains(jobject handle) const; // Does this block or following blocks contain handle bool contains(jobject handle) const; // Does this block contain handle int length() const; // Length of chain starting with this block long memory_usage() const; #ifndef PRODUCT static bool any_contains(jobject handle); // Does any block currently in use contain handle static void print_statistics(); #endif }; inline oop JNIHandles::resolve(jobject handle) { oop result = (handle == NULL ? (oop)NULL : *(oop*)handle); assert(result != NULL || (handle == NULL || !CheckJNICalls || is_weak_global_handle(handle)), "Invalid value read from jni handle"); assert(result != badJNIHandle, "Pointing to zapped jni handle area"); return result; }; inline oop JNIHandles::resolve_external_guard(jobject handle) { if (handle == NULL) return NULL; oop result = *(oop*)handle; if (result == NULL || result == badJNIHandle) return NULL; return result; }; inline oop JNIHandles::resolve_non_null(jobject handle) { assert(handle != NULL, "JNI handle should not be null"); oop result = *(oop*)handle; assert(result != NULL, "Invalid value read from jni handle"); assert(result != badJNIHandle, "Pointing to zapped jni handle area"); // Don't let that private _deleted_handle object escape into the wild. assert(result != deleted_handle(), "Used a deleted global handle."); return result; }; inline methodOop JNIHandles::resolve_jmethod_id(jmethodID mid) { return (methodOop) resolve_non_null((jobject)mid); }; inline methodOop JNIHandles::checked_resolve_jmethod_id(jmethodID mid) { oop o = resolve_external_guard((jobject) mid); if (o == NULL || !o->is_method()) { return (methodOop) NULL; } return (methodOop) o; }; inline void JNIHandles::destroy_local(jobject handle) { if (handle != NULL) { *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it } }