| // Copyright 2017 The Abseil Authors. | |
| // | |
| // 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 | |
| // | |
| // https://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. | |
| // | |
| // A simple thread-safe memory allocator that does not depend on | |
| // mutexes or thread-specific data. It is intended to be used | |
| // sparingly, and only when malloc() would introduce an unwanted | |
| // dependency, such as inside the heap-checker, or the Mutex | |
| // implementation. | |
| // IWYU pragma: private, include "base/low_level_alloc.h" | |
| // LowLevelAlloc requires that the platform support low-level | |
| // allocation of virtual memory. Platforms lacking this cannot use | |
| // LowLevelAlloc. | |
| // Using LowLevelAlloc with kAsyncSignalSafe isn't supported on Windows or | |
| // asm.js / WebAssembly. | |
| // See https://kripken.github.io/emscripten-site/docs/porting/pthreads.html | |
| // for more information. | |
| namespace absl { | |
| ABSL_NAMESPACE_BEGIN | |
| namespace base_internal { | |
| class LowLevelAlloc { | |
| public: | |
| struct Arena; // an arena from which memory may be allocated | |
| // Returns a pointer to a block of at least "request" bytes | |
| // that have been newly allocated from the specific arena. | |
| // for Alloc() call the DefaultArena() is used. | |
| // Returns 0 if passed request==0. | |
| // Does not return 0 under other circumstances; it crashes if memory | |
| // is not available. | |
| static void *Alloc(size_t request) ABSL_ATTRIBUTE_SECTION(malloc_hook); | |
| static void *AllocWithArena(size_t request, Arena *arena) | |
| ABSL_ATTRIBUTE_SECTION(malloc_hook); | |
| // Deallocates a region of memory that was previously allocated with | |
| // Alloc(). Does nothing if passed 0. "s" must be either 0, | |
| // or must have been returned from a call to Alloc() and not yet passed to | |
| // Free() since that call to Alloc(). The space is returned to the arena | |
| // from which it was allocated. | |
| static void Free(void *s) ABSL_ATTRIBUTE_SECTION(malloc_hook); | |
| // ABSL_ATTRIBUTE_SECTION(malloc_hook) for Alloc* and Free | |
| // are to put all callers of MallocHook::Invoke* in this module | |
| // into special section, | |
| // so that MallocHook::GetCallerStackTrace can function accurately. | |
| // Create a new arena. | |
| // The root metadata for the new arena is allocated in the | |
| // meta_data_arena; the DefaultArena() can be passed for meta_data_arena. | |
| // These values may be ored into flags: | |
| enum { | |
| // Report calls to Alloc() and Free() via the MallocHook interface. | |
| // Set in the DefaultArena. | |
| kCallMallocHook = 0x0001, | |
| // Make calls to Alloc(), Free() be async-signal-safe. Not set in | |
| // DefaultArena(). Not supported on all platforms. | |
| kAsyncSignalSafe = 0x0002, | |
| }; | |
| // Construct a new arena. The allocation of the underlying metadata honors | |
| // the provided flags. For example, the call NewArena(kAsyncSignalSafe) | |
| // is itself async-signal-safe, as well as generatating an arena that provides | |
| // async-signal-safe Alloc/Free. | |
| static Arena *NewArena(uint32_t flags); | |
| // Destroys an arena allocated by NewArena and returns true, | |
| // provided no allocated blocks remain in the arena. | |
| // If allocated blocks remain in the arena, does nothing and | |
| // returns false. | |
| // It is illegal to attempt to destroy the DefaultArena(). | |
| static bool DeleteArena(Arena *arena); | |
| // The default arena that always exists. | |
| static Arena *DefaultArena(); | |
| private: | |
| LowLevelAlloc(); // no instances | |
| }; | |
| } // namespace base_internal | |
| ABSL_NAMESPACE_END | |
| } // namespace absl | |