libc/src/pthread/pthread_spin_lock.cpp

   1 //===-- Implementation of pthread_spin_lock function ----------------------===//
   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/pthread/pthread_spin_lock.h"
  10 #include "hdr/errno_macros.h"
  11 #include "src/__support/common.h"
  12 #include "src/__support/threads/identifier.h"
  13 #include "src/__support/threads/spin_lock.h"
  14
  15 namespace LIBC_NAMESPACE_DECL {
  16
  17 static_assert(sizeof(pthread_spinlock_t::__lockword) == sizeof(SpinLock) &&
  18                   alignof(decltype(pthread_spinlock_t::__lockword)) ==
  19                       alignof(SpinLock),
  20               "pthread_spinlock_t::__lockword and SpinLock must be of the same "
  21               "size and alignment");
  22
  23 LLVM_LIBC_FUNCTION(int, pthread_spin_lock, (pthread_spinlock_t * lock)) {
  24   // If an implementation detects that the value specified by the lock argument
  25   // to pthread_spin_lock() or pthread_spin_trylock() does not refer to an
  26   // initialized spin lock object, it is recommended that the function should
  27   // fail and report an [EINVAL] error.
  28   if (!lock)
  29     return EINVAL;
  30   auto spin_lock = reinterpret_cast<SpinLock *>(&lock->__lockword);
  31   if (spin_lock->is_invalid())
  32     return EINVAL;
  33
  34   pid_t self_tid = internal::gettid();
  35   // If an implementation detects that the value specified by the lock argument
  36   // to pthread_spin_lock() refers to a spin lock object for which the calling
  37   // thread already holds the lock, it is recommended that the function should
  38   // fail and report an [EDEADLK] error.
  39   if (lock->__owner == self_tid)
  40     return EDEADLK;
  41
  42   spin_lock->lock();
  43   lock->__owner = self_tid;
  44   return 0;
  45 }
  46
  47 } // namespace LIBC_NAMESPACE_DECL