1 files changed, 149 insertions, 0 deletions
diff --git a/runtime/atomic.cc b/runtime/atomic.cc
new file mode 100644
index 0000000000..f2a998289c
--- /dev/null
+++ b/runtime/atomic.cc
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+/*
+ * Copyright (C) 2010 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "atomic.h"
+
+#define NEED_SWAP_MUTEXES !defined(__arm__) && !defined(__i386__)
+
+#if NEED_SWAP_MUTEXES
+#include <vector>
+#include "base/mutex.h"
+#include "base/stl_util.h"
+#include "base/stringprintf.h"
+#include "thread.h"
+#endif
+
+namespace art {
+
+#if NEED_SWAP_MUTEXES
+// We stripe across a bunch of different mutexes to reduce contention.
+static const size_t kSwapMutexCount = 32;
+static std::vector<Mutex*>* gSwapMutexes;
+
+static Mutex& GetSwapMutex(const volatile int64_t* addr) {
+  return *(*gSwapMutexes)[((unsigned)(void*)(addr) >> 3U) % kSwapMutexCount];
+}
+#endif
+
+void QuasiAtomic::Startup() {
+#if NEED_SWAP_MUTEXES
+  gSwapMutexes = new std::vector<Mutex*>;
+  for (size_t i = 0; i < kSwapMutexCount; ++i) {
+    gSwapMutexes->push_back(new Mutex("QuasiAtomic stripe"));
+  }
+#endif
+}
+
+void QuasiAtomic::Shutdown() {
+#if NEED_SWAP_MUTEXES
+  STLDeleteElements(gSwapMutexes);
+  delete gSwapMutexes;
+#endif
+}
+
+int64_t QuasiAtomic::Read64(volatile const int64_t* addr) {
+  int64_t value;
+#if NEED_SWAP_MUTEXES
+  MutexLock mu(Thread::Current(), GetSwapMutex(addr));
+  value = *addr;
+#elif defined(__arm__)
+  // Exclusive loads are defined not to tear, clearing the exclusive state isn't necessary. If we
+  // have LPAE (such as Cortex-A15) then ldrd would suffice.
+  __asm__ __volatile__("@ QuasiAtomic::Read64\n"
+      "ldrexd     %0, %H0, [%1]"
+      : "=&r" (value)
+      : "r" (addr));
+#elif defined(__i386__)
+  __asm__ __volatile__(
+      "movq     %1, %0\n"
+      : "=x" (value)
+      : "m" (*addr));
+#else
+#error Unexpected architecture
+#endif
+  return value;
+}
+
+void QuasiAtomic::Write64(volatile int64_t* addr, int64_t value) {
+#if NEED_SWAP_MUTEXES
+  MutexLock mu(Thread::Current(), GetSwapMutex(addr));
+  *addr = value;
+#elif defined(__arm__)
+  // The write is done as a swap so that the cache-line is in the exclusive state for the store. If
+  // we know that ARM architecture has LPAE (such as Cortex-A15) this isn't necessary and strd will
+  // suffice.
+  int64_t prev;
+  int status;
+  do {
+    __asm__ __volatile__("@ QuasiAtomic::Write64\n"
+        "ldrexd     %0, %H0, [%3]\n"
+        "strexd     %1, %4, %H4, [%3]"
+        : "=&r" (prev), "=&r" (status), "+m"(*addr)
+        : "r" (addr), "r" (value)
+        : "cc");
+  } while (__builtin_expect(status != 0, 0));
+#elif defined(__i386__)
+  __asm__ __volatile__(
+      "movq     %1, %0"
+      : "=m" (*addr)
+      : "x" (value));
+#else
+#error Unexpected architecture
+#endif
+}
+
+
+bool QuasiAtomic::Cas64(int64_t old_value, int64_t new_value, volatile int64_t* addr) {
+#if NEED_SWAP_MUTEXES
+  MutexLock mu(Thread::Current(), GetSwapMutex(addr));
+  if (*addr == old_value) {
+    *addr = new_value;
+    return true;
+  }
+  return false;
+#elif defined(__arm__)
+  int64_t prev;
+  int status;
+  do {
+    __asm__ __volatile__("@ QuasiAtomic::Cas64\n"
+        "ldrexd     %0, %H0, [%3]\n"
+        "mov        %1, #0\n"
+        "teq        %0, %4\n"
+        "teqeq      %H0, %H4\n"
+        "strexdeq   %1, %5, %H5, [%3]"
+        : "=&r" (prev), "=&r" (status), "+m"(*addr)
+        : "r" (addr), "Ir" (old_value), "r" (new_value)
+        : "cc");
+  } while (__builtin_expect(status != 0, 0));
+  return prev == old_value;
+#elif defined(__i386__)
+  // The compiler does the right job and works better than inline assembly, especially with -O0
+  // compilation.
+  return __sync_bool_compare_and_swap(addr, old_value, new_value);
+#else
+#error Unexpected architecture
+#endif
+}
+
+bool QuasiAtomic::LongAtomicsUseMutexes() {
+#if NEED_SWAP_MUTEXES
+  return true;
+#else
+  return false;
+#endif
+}
+
+}  // namespace art