libc/src/stdlib/atexit.cpp

   1 //===-- Implementation of atexit ------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "src/stdlib/atexit.h"
  10 #include "src/__support/blockstore.h"
  11 #include "src/__support/common.h"
  12 #include "src/__support/fixedvector.h"
  13 #include "src/__support/threads/mutex.h"
  14
  15 namespace LIBC_NAMESPACE {
  16
  17 namespace {
  18
  19 Mutex handler_list_mtx(false, false, false);
  20
  21 using AtExitCallback = void(void *);
  22 using StdCAtExitCallback = void(void);
  23
  24 struct AtExitUnit {
  25   AtExitCallback *callback = nullptr;
  26   void *payload = nullptr;
  27   constexpr AtExitUnit() = default;
  28   constexpr AtExitUnit(AtExitCallback *c, void *p) : callback(c), payload(p) {}
  29 };
  30
  31 #ifdef LIBC_COPT_PUBLIC_PACKAGING
  32 using ExitCallbackList = cpp::ReverseOrderBlockStore<AtExitUnit, 32>;
  33 #else
  34 // BlockStore uses dynamic memory allocation. To avoid dynamic memory
  35 // allocation in tests, we use a fixed size callback list when built for
  36 // tests.
  37 // If we use BlockStore, then we will have to pull in malloc etc into
  38 // the tests. While this is not bad, the problem we have currently is
  39 // that LLVM libc' allocator is SCUDO. So, we will end up pulling SCUDO's
  40 // deps also (some of which are not yet available in LLVM libc) into the
  41 // integration tests.
  42 using ExitCallbackList = FixedVector<AtExitUnit, CALLBACK_LIST_SIZE_FOR_TESTS>;
  43 #endif // LIBC_COPT_PUBLIC_PACKAGING
  44
  45 constinit ExitCallbackList exit_callbacks;
  46
  47 void stdc_at_exit_func(void *payload) {
  48   reinterpret_cast<StdCAtExitCallback *>(payload)();
  49 }
  50
  51 } // namespace
  52
  53 namespace internal {
  54
  55 void call_exit_callbacks() {
  56   handler_list_mtx.lock();
  57   while (!exit_callbacks.empty()) {
  58     auto unit = exit_callbacks.back();
  59     exit_callbacks.pop_back();
  60     handler_list_mtx.unlock();
  61     unit.callback(unit.payload);
  62     handler_list_mtx.lock();
  63   }
  64   ExitCallbackList::destroy(&exit_callbacks);
  65 }
  66
  67 } // namespace internal
  68
  69 static int add_atexit_unit(const AtExitUnit &unit) {
  70   MutexLock lock(&handler_list_mtx);
  71   if (!exit_callbacks.push_back(unit))
  72     return -1;
  73   return 0;
  74 }
  75
  76 // TODO: Handle the last dso handle argument.
  77 extern "C" int __cxa_atexit(AtExitCallback *callback, void *payload, void *) {
  78   return add_atexit_unit({callback, payload});
  79 }
  80
  81 LLVM_LIBC_FUNCTION(int, atexit, (StdCAtExitCallback * callback)) {
  82   return add_atexit_unit(
  83       {&stdc_at_exit_func, reinterpret_cast<void *>(callback)});
  84 }
  85
  86 } // namespace LIBC_NAMESPACE