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//===-- Linux implementation of the thrd_join function --------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "config/linux/syscall.h" // For syscall function.
#include "include/sys/syscall.h" // For syscall numbers.
#include "include/threads.h" // For thrd_* type definitions.
#include "src/__support/common.h"
#include "src/sys/mman/munmap.h"
#include "src/threads/linux/thread_utils.h"
#include <linux/futex.h> // For futex operations.
#include <stdatomic.h> // For atomic_load.
namespace __llvm_libc {
int LLVM_LIBC_ENTRYPOINT(thrd_join)(thrd_t *thread, int *retval) {
FutexData *clear_tid_address =
reinterpret_cast<FutexData *>(thread->__clear_tid);
// The kernel should set the value at the clear tid address to zero.
// If not, it is a spurious wake and we should continue to wait on
// the futex.
while (atomic_load(clear_tid_address) != 0) {
// We cannot do a FUTEX_WAIT_PRIVATE here as the kernel does a
// FUTEX_WAKE and not a FUTEX_WAKE_PRIVATE.
__llvm_libc::syscall(SYS_futex, clear_tid_address, FUTEX_WAIT,
ThreadParams::ClearTIDValue, nullptr);
}
*retval = thread->__retval;
if (__llvm_libc::munmap(thread->__stack, thread->__stack_size) == -1)
return thrd_error;
return thrd_success;
}
} // namespace __llvm_libc
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