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127 lines
4.6 KiB
127 lines
4.6 KiB
// Copyright 2017 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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#ifndef ABSL_BASE_INTERNAL_LOW_LEVEL_ALLOC_H_
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#define ABSL_BASE_INTERNAL_LOW_LEVEL_ALLOC_H_
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// A simple thread-safe memory allocator that does not depend on
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// mutexes or thread-specific data. It is intended to be used
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// sparingly, and only when malloc() would introduce an unwanted
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// dependency, such as inside the heap-checker, or the Mutex
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// implementation.
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// IWYU pragma: private, include "base/low_level_alloc.h"
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#include <sys/types.h>
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#include <cstdint>
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#include "absl/base/attributes.h"
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#include "absl/base/config.h"
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// LowLevelAlloc requires that the platform support low-level
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// allocation of virtual memory. Platforms lacking this cannot use
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// LowLevelAlloc.
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#ifdef ABSL_LOW_LEVEL_ALLOC_MISSING
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#error ABSL_LOW_LEVEL_ALLOC_MISSING cannot be directly set
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#elif !defined(ABSL_HAVE_MMAP) && !defined(_WIN32)
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#define ABSL_LOW_LEVEL_ALLOC_MISSING 1
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#endif
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// Using LowLevelAlloc with kAsyncSignalSafe isn't supported on Windows or
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// asm.js / WebAssembly.
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// See https://kripken.github.io/emscripten-site/docs/porting/pthreads.html
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// for more information.
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#ifdef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
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#error ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING cannot be directly set
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#elif defined(_WIN32) || defined(__asmjs__) || defined(__wasm__)
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#define ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING 1
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#endif
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#include <cstddef>
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#include "absl/base/port.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace base_internal {
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class LowLevelAlloc {
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public:
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struct Arena; // an arena from which memory may be allocated
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// Returns a pointer to a block of at least "request" bytes
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// that have been newly allocated from the specific arena.
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// for Alloc() call the DefaultArena() is used.
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// Returns 0 if passed request==0.
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// Does not return 0 under other circumstances; it crashes if memory
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// is not available.
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static void *Alloc(size_t request) ABSL_ATTRIBUTE_SECTION(malloc_hook);
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static void *AllocWithArena(size_t request, Arena *arena)
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ABSL_ATTRIBUTE_SECTION(malloc_hook);
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// Deallocates a region of memory that was previously allocated with
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// Alloc(). Does nothing if passed 0. "s" must be either 0,
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// or must have been returned from a call to Alloc() and not yet passed to
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// Free() since that call to Alloc(). The space is returned to the arena
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// from which it was allocated.
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static void Free(void *s) ABSL_ATTRIBUTE_SECTION(malloc_hook);
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// ABSL_ATTRIBUTE_SECTION(malloc_hook) for Alloc* and Free
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// are to put all callers of MallocHook::Invoke* in this module
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// into special section,
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// so that MallocHook::GetCallerStackTrace can function accurately.
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// Create a new arena.
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// The root metadata for the new arena is allocated in the
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// meta_data_arena; the DefaultArena() can be passed for meta_data_arena.
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// These values may be ored into flags:
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enum {
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// Report calls to Alloc() and Free() via the MallocHook interface.
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// Set in the DefaultArena.
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kCallMallocHook = 0x0001,
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#ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
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// Make calls to Alloc(), Free() be async-signal-safe. Not set in
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// DefaultArena(). Not supported on all platforms.
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kAsyncSignalSafe = 0x0002,
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#endif
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};
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// Construct a new arena. The allocation of the underlying metadata honors
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// the provided flags. For example, the call NewArena(kAsyncSignalSafe)
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// is itself async-signal-safe, as well as generatating an arena that provides
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// async-signal-safe Alloc/Free.
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static Arena *NewArena(int32_t flags);
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// Destroys an arena allocated by NewArena and returns true,
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// provided no allocated blocks remain in the arena.
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// If allocated blocks remain in the arena, does nothing and
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// returns false.
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// It is illegal to attempt to destroy the DefaultArena().
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static bool DeleteArena(Arena *arena);
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// The default arena that always exists.
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static Arena *DefaultArena();
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private:
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LowLevelAlloc(); // no instances
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};
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} // namespace base_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_BASE_INTERNAL_LOW_LEVEL_ALLOC_H_
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