/* * Copyright (c) 1999, 2016, 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. * * 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. * */ #ifndef SHARE_VM_RUNTIME_ATOMIC_HPP #define SHARE_VM_RUNTIME_ATOMIC_HPP #include "memory/allocation.hpp" #include "utilities/macros.hpp" enum cmpxchg_memory_order { memory_order_relaxed, // Use value which doesn't interfere with C++2011. We need to be more conservative. memory_order_conservative = 8 }; class Atomic : AllStatic { public: // Atomic operations on jlong types are not available on all 32-bit // platforms. If atomic ops on jlongs are defined here they must only // be used from code that verifies they are available at runtime and // can provide an alternative action if not - see supports_cx8() for // a means to test availability. // The memory operations that are mentioned with each of the atomic // function families come from src/share/vm/runtime/orderAccess.hpp, // e.g., is described in that file and is implemented by the // OrderAccess::fence() function. See that file for the gory details // on the Memory Access Ordering Model. // All of the atomic operations that imply a read-modify-write action // guarantee a two-way memory barrier across that operation. Historically // these semantics reflect the strength of atomic operations that are // provided on SPARC/X86. We assume that strength is necessary unless // we can prove that a weaker form is sufficiently safe. // Atomically store to a location inline static void store (jbyte store_value, jbyte* dest); inline static void store (jshort store_value, jshort* dest); inline static void store (jint store_value, jint* dest); // See comment above about using jlong atomics on 32-bit platforms inline static void store (jlong store_value, jlong* dest); inline static void store_ptr(intptr_t store_value, intptr_t* dest); inline static void store_ptr(void* store_value, void* dest); inline static void store (jbyte store_value, volatile jbyte* dest); inline static void store (jshort store_value, volatile jshort* dest); inline static void store (jint store_value, volatile jint* dest); // See comment above about using jlong atomics on 32-bit platforms inline static void store (jlong store_value, volatile jlong* dest); inline static void store_ptr(intptr_t store_value, volatile intptr_t* dest); inline static void store_ptr(void* store_value, volatile void* dest); // See comment above about using jlong atomics on 32-bit platforms inline static jlong load(volatile jlong* src); // Atomically add to a location. Returns updated value. add*() provide: // add-value-to-dest inline static jint add (jint add_value, volatile jint* dest); inline static size_t add (size_t add_value, volatile size_t* dest); inline static intptr_t add_ptr(intptr_t add_value, volatile intptr_t* dest); inline static void* add_ptr(intptr_t add_value, volatile void* dest); // See comment above about using jlong atomics on 32-bit platforms inline static jlong add (jlong add_value, volatile jlong* dest); // Atomically increment location. inc*() provide: // increment-dest inline static void inc (volatile jint* dest); inline static jint inc (volatile jshort* dest); inline static void inc (volatile size_t* dest); inline static void inc_ptr(volatile intptr_t* dest); inline static void inc_ptr(volatile void* dest); // Atomically decrement a location. dec*() provide: // decrement-dest inline static void dec (volatile jint* dest); inline static jint dec (volatile jshort* dest); inline static void dec (volatile size_t* dest); inline static void dec_ptr(volatile intptr_t* dest); inline static void dec_ptr(volatile void* dest); // Performs atomic exchange of *dest with exchange_value. Returns old // prior value of *dest. xchg*() provide: // exchange-value-with-dest inline static jint xchg (jint exchange_value, volatile jint* dest); inline static unsigned int xchg (unsigned int exchange_value, volatile unsigned int* dest); inline static intptr_t xchg_ptr(intptr_t exchange_value, volatile intptr_t* dest); inline static void* xchg_ptr(void* exchange_value, volatile void* dest); // Performs atomic compare of *dest and compare_value, and exchanges // *dest with exchange_value if the comparison succeeded. Returns prior // value of *dest. cmpxchg*() provide: // compare-and-exchange inline static jbyte cmpxchg (jbyte exchange_value, volatile jbyte* dest, jbyte compare_value, cmpxchg_memory_order order = memory_order_conservative); inline static jint cmpxchg (jint exchange_value, volatile jint* dest, jint compare_value, cmpxchg_memory_order order = memory_order_conservative); // See comment above about using jlong atomics on 32-bit platforms inline static jlong cmpxchg (jlong exchange_value, volatile jlong* dest, jlong compare_value, cmpxchg_memory_order order = memory_order_conservative); inline static unsigned int cmpxchg (unsigned int exchange_value, volatile unsigned int* dest, unsigned int compare_value, cmpxchg_memory_order order = memory_order_conservative); inline static intptr_t cmpxchg_ptr(intptr_t exchange_value, volatile intptr_t* dest, intptr_t compare_value, cmpxchg_memory_order order = memory_order_conservative); inline static void* cmpxchg_ptr(void* exchange_value, volatile void* dest, void* compare_value, cmpxchg_memory_order order = memory_order_conservative); }; // platform specific in-line definitions - must come before shared definitions #include OS_CPU_HEADER(atomic) // shared in-line definitions // size_t casts... #if (SIZE_MAX != UINTPTR_MAX) #error size_t is not WORD_SIZE, interesting platform, but missing implementation here #endif inline size_t Atomic::add(size_t add_value, volatile size_t* dest) { return (size_t) add_ptr((intptr_t) add_value, (volatile intptr_t*) dest); } inline void Atomic::inc(volatile size_t* dest) { inc_ptr((volatile intptr_t*) dest); } inline void Atomic::dec(volatile size_t* dest) { dec_ptr((volatile intptr_t*) dest); } #ifndef VM_HAS_SPECIALIZED_CMPXCHG_BYTE /* * This is the default implementation of byte-sized cmpxchg. It emulates jbyte-sized cmpxchg * in terms of jint-sized cmpxchg. Platforms may override this by defining their own inline definition * as well as defining VM_HAS_SPECIALIZED_CMPXCHG_BYTE. This will cause the platform specific * implementation to be used instead. */ inline jbyte Atomic::cmpxchg(jbyte exchange_value, volatile jbyte *dest, jbyte comparand, cmpxchg_memory_order order) { assert(sizeof(jbyte) == 1, "assumption."); uintptr_t dest_addr = (uintptr_t)dest; uintptr_t offset = dest_addr % sizeof(jint); volatile jint* dest_int = (volatile jint*)(dest_addr - offset); jint cur = *dest_int; jbyte* cur_as_bytes = (jbyte*)(&cur); jint new_val = cur; jbyte* new_val_as_bytes = (jbyte*)(&new_val); new_val_as_bytes[offset] = exchange_value; while (cur_as_bytes[offset] == comparand) { jint res = cmpxchg(new_val, dest_int, cur, order); if (res == cur) break; cur = res; new_val = cur; new_val_as_bytes[offset] = exchange_value; } return cur_as_bytes[offset]; } #endif // VM_HAS_SPECIALIZED_CMPXCHG_BYTE inline unsigned Atomic::xchg(unsigned int exchange_value, volatile unsigned int* dest) { assert(sizeof(unsigned int) == sizeof(jint), "more work to do"); return (unsigned int)Atomic::xchg((jint)exchange_value, (volatile jint*)dest); } inline unsigned Atomic::cmpxchg(unsigned int exchange_value, volatile unsigned int* dest, unsigned int compare_value, cmpxchg_memory_order order) { assert(sizeof(unsigned int) == sizeof(jint), "more work to do"); return (unsigned int)Atomic::cmpxchg((jint)exchange_value, (volatile jint*)dest, (jint)compare_value, order); } inline jlong Atomic::add(jlong add_value, volatile jlong* dest) { jlong old = load(dest); jlong new_value = old + add_value; while (old != cmpxchg(new_value, dest, old)) { old = load(dest); new_value = old + add_value; } return old; } inline jint Atomic::inc(volatile short* dest) { // Most platforms do not support atomic increment on a 2-byte value. However, // if the value occupies the most significant 16 bits of an aligned 32-bit // word, then we can do this with an atomic add of 0x10000 to the 32-bit word. // // The least significant parts of this 32-bit word will never be affected, even // in case of overflow/underflow. // // Use the ATOMIC_SHORT_PAIR macro (see macros.hpp) to get the desired alignment. #ifdef VM_LITTLE_ENDIAN assert((intx(dest) & 0x03) == 0x02, "wrong alignment"); jint new_value = Atomic::add(0x10000, (volatile int*)(dest-1)); #else assert((intx(dest) & 0x03) == 0x00, "wrong alignment"); jint new_value = Atomic::add(0x10000, (volatile int*)(dest)); #endif return new_value >> 16; // preserves sign } inline jint Atomic::dec(volatile short* dest) { #ifdef VM_LITTLE_ENDIAN assert((intx(dest) & 0x03) == 0x02, "wrong alignment"); jint new_value = Atomic::add(-0x10000, (volatile int*)(dest-1)); #else assert((intx(dest) & 0x03) == 0x00, "wrong alignment"); jint new_value = Atomic::add(-0x10000, (volatile int*)(dest)); #endif return new_value >> 16; // preserves sign } #endif // SHARE_VM_RUNTIME_ATOMIC_HPP