objc4-781.tar.gz

[apple/objc4.git] / runtime / objc-zalloc.h

diff --git a/runtime/objc-zalloc.h b/runtime/objc-zalloc.h
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+/*
+ * Copyright (c) 2019 Apple Inc.  All Rights Reserved.
+ * 
+ * @APPLE_LICENSE_HEADER_START@
+ * 
+ * This file contains Original Code and/or Modifications of Original Code
+ * as defined in and that are subject to the Apple Public Source License
+ * Version 2.0 (the 'License'). You may not use this file except in
+ * compliance with the License. Please obtain a copy of the License at
+ * http://www.opensource.apple.com/apsl/ and read it before using this
+ * file.
+ * 
+ * The Original Code and all software distributed under the License are
+ * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
+ * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
+ * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
+ * Please see the License for the specific language governing rights and
+ * limitations under the License.
+ * 
+ * @APPLE_LICENSE_HEADER_END@
+ */
+
+/**
+ * @file objc-zalloc.h
+ *
+ * "zone allocator" for objc.
+ *
+ * Provides packed allocation for data structures the runtime
+ * almost never frees.
+ */
+
+#ifndef _OBJC_ZALLOC_H
+#define _OBJC_ZALLOC_H
+
+#include <cstdint>
+#include <atomic>
+#include <cstdlib>
+
+namespace objc {
+
+// Darwin malloc always aligns to 16 bytes
+#define MALLOC_ALIGNMENT 16
+
+class AtomicQueue {
+#if __LP64__
+    using pair_t = __int128_t;
+#else
+    using pair_t = uint64_t;
+#endif
+    static constexpr auto relaxed = std::memory_order_relaxed;
+    static constexpr auto release = std::memory_order_release;
+
+    struct Entry {
+        struct Entry *next;
+    };
+
+    union {
+        struct {
+            Entry        *head;
+            unsigned long gen;
+        };
+        std::atomic<pair_t> atomic_pair;
+        pair_t pair;
+    };
+
+public:
+    void *pop();
+    void push_list(void *_head, void *_tail);
+    inline void push(void *head)
+    {
+        push_list(head, head);
+    }
+};
+
+template<class T, bool useMalloc>
+class Zone {
+};
+
+template<class T>
+class Zone<T, false> {
+    struct Element {
+        Element *next;
+        char buf[sizeof(T) - sizeof(void *)];
+    } __attribute__((packed));
+
+    static AtomicQueue _freelist;
+    static T *alloc_slow();
+
+public:
+    static T *alloc();
+    static void free(T *);
+};
+
+template<class T>
+class Zone<T, true> {
+public:
+    static inline T *alloc() {
+        return reinterpret_cast<T *>(::calloc(sizeof(T), 1));
+    }
+    static inline void free(T *ptr) {
+        ::free(ptr);
+    }
+};
+
+/*
+ * This allocator returns always zeroed memory,
+ * and the template needs to be instantiated in objc-zalloc.mm
+ */
+
+template<class T>
+T *zalloc()
+{
+    return Zone<T, sizeof(T) % MALLOC_ALIGNMENT == 0>::alloc();
+}
+
+template<class T>
+void zfree(T *e)
+{
+    Zone<T, sizeof(T) % MALLOC_ALIGNMENT == 0>::free(e);
+}
+
+};
+
+#endif