[libc] Reland #148948 "Implement barriers for pthreads" (#151021)

Fixed build dependencies for pthread_barrier_t (add __barrier_type to
cmake dependencies)

libc/config/linux/x86_64/entrypoints.txt

@@ -1056,6 +1056,9 @@ if(LLVM_LIBC_FULL_BUILD)
     libc.src.pthread.pthread_join
     libc.src.pthread.pthread_key_create
     libc.src.pthread.pthread_key_delete
+    libc.src.pthread.pthread_barrier_init
+    libc.src.pthread.pthread_barrier_wait
+    libc.src.pthread.pthread_barrier_destroy
     libc.src.pthread.pthread_mutex_destroy
     libc.src.pthread.pthread_mutex_init
     libc.src.pthread.pthread_mutex_lock

libc/hdr/CMakeLists.txt

@@ -72,6 +72,15 @@ add_proxy_header_library(
     libc.include.fenv
 )
 
+add_proxy_header_library(
+  pthread_macros
+  HDRS
+    pthread_macros.h
+  FULL_BUILD_DEPENDS
+    libc.include.llvm-libc-macros.pthread_macros
+    libc.include.pthread
+)
+
 add_proxy_header_library(
   sched_macros
   HDRS

libc/hdr/pthread_macros.h

@@ -0,0 +1,22 @@
+//===-- Definition of macros from pthread.h -------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_HDR_PTHREAD_MACROS_H
+#define LLVM_LIBC_HDR_PTHREAD_MACROS_H
+
+#ifdef LIBC_FULL_BUILD
+
+#include "include/llvm-libc-macros/pthread-macros.h"
+
+#else // Overlay mode
+
+#include <pthread.h>
+
+#endif // LLVM_LIBC_FULL_BUILD
+
+#endif // LLVM_LIBC_HDR_PTHREAD_MACROS_H

libc/hdr/types/CMakeLists.txt

@@ -241,6 +241,22 @@ add_proxy_header_library(
     libc.include.llvm-libc-types.pid_t
 )
 
+add_proxy_header_library(
+  pthread_barrier_t
+  HDRS
+    pthread_barrier_t.h
+  FULL_BUILD_DEPENDS
+    libc.include.llvm-libc-types.pthread_barrier_t
+)
+
+add_proxy_header_library(
+  pthread_barrierattr_t
+  HDRS
+    pthread_barrierattr_t.h
+  FULL_BUILD_DEPENDS
+    libc.include.llvm-libc-types.pthread_barrierattr_t
+)
+
 add_proxy_header_library(
   atexithandler_t
   HDRS

libc/hdr/types/pthread_barrier_t.h

@@ -0,0 +1,22 @@
+//===-- Definition of macros from pthread_barrier_t.h ---------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_HDR_TYPES_PTHREAD_BARRIER_T_H
+#define LLVM_LIBC_HDR_TYPES_PTHREAD_BARRIER_T_H
+
+#ifdef LIBC_FULL_BUILD
+
+#include "include/llvm-libc-types/pthread_barrier_t.h"
+
+#else // Overlay mode
+
+#error "Cannot overlay pthread_barrier_t"
+
+#endif // LLVM_LIBC_FULL_BUILD
+
+#endif // LLVM_LIBC_HDR_TYPES_PTHREAD_BARRIER_T_H

libc/hdr/types/pthread_barrierattr_t.h

@@ -0,0 +1,22 @@
+//===-- Definition of macros from pthread_barrierattr_t.h -----------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_HDR_TYPES_PTHREAD_BARRIERATTR_T_H
+#define LLVM_LIBC_HDR_TYPES_PTHREAD_BARRIERATTR_T_H
+
+#ifdef LIBC_FULL_BUILD
+
+#include "include/llvm-libc-types/pthread_barrierattr_t.h"
+
+#else // Overlay mode
+
+#error "Cannot overlay pthread_barrierattr_t"
+
+#endif // LLVM_LIBC_FULL_BUILD
+
+#endif // LLVM_LIBC_HDR_TYPES_PTHREAD_BARRIERATTR_T_H

libc/include/CMakeLists.txt

@@ -392,6 +392,8 @@ add_header_macro(
     .llvm-libc-types.pthread_attr_t
     .llvm-libc-types.pthread_condattr_t
     .llvm-libc-types.pthread_key_t
+    .llvm-libc-types.pthread_barrier_t
+    .llvm-libc-types.pthread_barrierattr_t
     .llvm-libc-types.pthread_mutex_t
     .llvm-libc-types.pthread_mutexattr_t
     .llvm-libc-types.pthread_once_t

libc/include/llvm-libc-macros/pthread-macros.h

@@ -22,6 +22,8 @@
 #define PTHREAD_MUTEX_STALLED 0
 #define PTHREAD_MUTEX_ROBUST 1
 
+#define PTHREAD_BARRIER_SERIAL_THREAD -1
+
 #define PTHREAD_ONCE_INIT {0}
 
 #define PTHREAD_PROCESS_PRIVATE 0

libc/include/llvm-libc-types/CMakeLists.txt

@@ -10,6 +10,7 @@ add_header(__exec_envp_t HDR __exec_envp_t.h)
 add_header(__futex_word HDR __futex_word.h)
 add_header(pid_t HDR pid_t.h)
 add_header(__mutex_type HDR __mutex_type.h DEPENDS .__futex_word .pid_t)
+add_header(__barrier_type HDR __barrier_type.h)
 add_header(__pthread_once_func_t HDR __pthread_once_func_t.h)
 add_header(__pthread_start_t HDR __pthread_start_t.h)
 add_header(__pthread_tss_dtor_t HDR __pthread_tss_dtor_t.h)
@@ -53,6 +54,8 @@ add_header(pthread_condattr_t HDR pthread_condattr_t.h DEPENDS .clockid_t)
 add_header(pthread_key_t HDR pthread_key_t.h)
 add_header(pthread_mutex_t HDR pthread_mutex_t.h DEPENDS .__futex_word .__mutex_type)
 add_header(pthread_mutexattr_t HDR pthread_mutexattr_t.h)
+add_header(pthread_barrier_t HDR pthread_barrier_t.h DEPENDS .__barrier_type)
+add_header(pthread_barrierattr_t HDR pthread_barrierattr_t.h)
 add_header(pthread_once_t HDR pthread_once_t.h DEPENDS .__futex_word)
 add_header(pthread_rwlock_t HDR pthread_rwlock_t.h DEPENDS .__futex_word .pid_t)
 add_header(pthread_rwlockattr_t HDR pthread_rwlockattr_t.h)

libc/include/llvm-libc-types/__barrier_type.h

@@ -0,0 +1,21 @@
+//===-- Definition of __barrier_type type ---------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_TYPES__BARRIER_TYPE_H
+#define LLVM_LIBC_TYPES__BARRIER_TYPE_H
+
+typedef struct __attribute__((aligned(8 /* alignof (Barrier) */))) {
+  unsigned expected;
+  unsigned waiting;
+  bool blocking;
+  char entering[24 /* sizeof (CndVar) */];
+  char exiting[24 /* sizeof (CndVar) */];
+  char mutex[24 /* sizeof (Mutex) */];
+} __barrier_type;
+
+#endif // LLVM_LIBC_TYPES__BARRIER_TYPE_H

libc/include/llvm-libc-types/pthread_barrier_t.h

@@ -0,0 +1,15 @@
+//===-- Definition of pthread_barrier_t type --------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_TYPES_PTHREAD_BARRIER_T_H
+#define LLVM_LIBC_TYPES_PTHREAD_BARRIER_T_H
+
+#include "__barrier_type.h"
+typedef __barrier_type pthread_barrier_t;
+
+#endif // LLVM_LIBC_TYPES_PTHREAD_BARRIER_T_H

libc/include/llvm-libc-types/pthread_barrierattr_t.h

@@ -0,0 +1,16 @@
+//===-- Definition of pthread_barrierattr_t type --------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_TYPES_PTHREAD_BARRIERATTR_T_H
+#define LLVM_LIBC_TYPES_PTHREAD_BARRIERATTR_T_H
+
+typedef struct {
+  bool pshared;
+} pthread_barrierattr_t;
+
+#endif // LLVM_LIBC_TYPES_PTHREAD_BARRIERATTR_T_H

libc/include/pthread.yaml

@@ -6,6 +6,8 @@ types:
   - type_name: pthread_once_t
   - type_name: pthread_mutex_t
   - type_name: pthread_mutexattr_t
+  - type_name: pthread_barrier_t
+  - type_name: pthread_barrierattr_t
   - type_name: pthread_key_t
   - type_name: pthread_condattr_t
   - type_name: __pthread_tss_dtor_t
@@ -277,6 +279,26 @@ functions:
     arguments:
       - type: pthread_mutexattr_t *__restrict
       - type: int
+  - name: pthread_barrier_init
+    standards:
+      - POSIX
+    return_type: int
+    arguments:
+      - type: pthread_barrier_t *__restrict
+      - type: const pthread_barrierattr_t *__restrict
+      - type: int
+  - name: pthread_barrier_wait
+    standards:
+      - POSIX
+    return_type: int
+    arguments:
+      - type: pthread_barrier_t *
+  - name: pthread_barrier_destroy
+    standards:
+      - POSIX
+    return_type: int
+    arguments:
+      - type: pthread_barrier_t *
   - name: pthread_once
     standards:
       - POSIX

libc/src/__support/threads/linux/CMakeLists.txt

@@ -124,3 +124,14 @@ add_object_library(
     libc.src.__support.threads.linux.raw_mutex
     libc.src.__support.CPP.mutex
 )
+
+add_object_library(
+  barrier
+  HDRS
+    barrier.h
+  SRCS
+    barrier.cpp
+  DEPENDS
+    libc.src.__support.threads.CndVar
+    libc.src.__support.threads.mutex
+)

libc/src/__support/threads/linux/barrier.cpp

@@ -0,0 +1,85 @@
+//===-- Implementation of Barrier class ------------- ---------------------===//
+//
+// 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 "src/__support/threads/linux/barrier.h"
+#include "hdr/errno_macros.h"
+#include "src/__support/threads/CndVar.h"
+#include "src/__support/threads/mutex.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int Barrier::init(Barrier *b,
+                  [[maybe_unused]] const pthread_barrierattr_t *attr,
+                  unsigned count) {
+  LIBC_ASSERT(attr == nullptr); // TODO implement barrierattr
+  if (count == 0)
+    return EINVAL;
+
+  b->expected = count;
+  b->waiting = 0;
+  b->blocking = true;
+
+  int err;
+  err = CndVar::init(&b->entering);
+  if (err != 0)
+    return err;
+
+  err = CndVar::init(&b->exiting);
+  if (err != 0)
+    return err;
+
+  auto mutex_err = Mutex::init(&b->m, false, false, false, false);
+  if (mutex_err != MutexError::NONE)
+    return EAGAIN;
+
+  return 0;
+}
+
+int Barrier::wait() {
+  m.lock();
+
+  // if the barrier is emptying out threads, wait until it finishes
+  while (!blocking)
+    entering.wait(&m);
+  waiting++;
+
+  if (waiting < expected) {
+    // block threads until waiting = expected
+    while (blocking)
+      exiting.wait(&m);
+  } else {
+    // this is the last thread to call wait(), so lets wake everyone up
+    blocking = false;
+    exiting.broadcast();
+  }
+  waiting--;
+
+  if (waiting == 0) {
+    // all threads have exited the barrier, let's let the ones waiting to enter
+    // continue
+    blocking = true;
+    entering.broadcast();
+    m.unlock();
+
+    // POSIX dictates that the barrier should return a special value to just one
+    // thread, so we can arbitrarily choose this thread
+    return PTHREAD_BARRIER_SERIAL_THREAD;
+  }
+  m.unlock();
+
+  return 0;
+}
+
+int Barrier::destroy(Barrier *b) {
+  CndVar::destroy(&b->entering);
+  CndVar::destroy(&b->exiting);
+  Mutex::destroy(&b->m);
+  return 0;
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/__support/threads/linux/barrier.h

@@ -0,0 +1,50 @@
+//===-- A platform independent abstraction layer for barriers --*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC___SUPPORT_SRC_THREADS_LINUX_BARRIER_H
+#define LLVM_LIBC___SUPPORT_SRC_THREADS_LINUX_BARRIER_H
+
+#include "hdr/pthread_macros.h"
+#include "include/llvm-libc-types/pthread_barrier_t.h"
+#include "include/llvm-libc-types/pthread_barrierattr_t.h"
+#include "src/__support/threads/CndVar.h"
+#include "src/__support/threads/mutex.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+// NOTE: if the size of this class changes, you must ensure that the size of
+// pthread_barrier_t (found in include/llvm-libc/types/pthread_barrier_t.h) is
+// the same size
+class Barrier {
+private:
+  unsigned expected;
+  unsigned waiting;
+  bool blocking;
+  CndVar entering;
+  CndVar exiting;
+  Mutex m;
+
+public:
+  static int init(Barrier *b, const pthread_barrierattr_t *attr,
+                  unsigned count);
+  static int destroy(Barrier *b);
+  int wait();
+};
+
+static_assert(
+    sizeof(Barrier) == sizeof(pthread_barrier_t),
+    "The public pthread_barrier_t type cannot accommodate the internal "
+    "barrier type.");
+
+static_assert(alignof(Barrier) == alignof(pthread_barrier_t),
+              "The public pthread_barrier_t type has a different alignment "
+              "than the internal barrier type.");
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC___SUPPORT_SRC_THREADS_LINUX_BARRIER_H

libc/src/pthread/CMakeLists.txt

@@ -272,6 +272,40 @@ add_entrypoint_object(
     libc.src.errno.errno
 )
 
+add_entrypoint_object(
+  pthread_barrier_init
+  SRCS
+    pthread_barrier_init.cpp
+  HDRS
+    pthread_barrier_init.h
+  DEPENDS
+    libc.src.errno.errno
+    libc.include.pthread
+    libc.src.__support.threads.linux.barrier
+)
+
+add_entrypoint_object(
+  pthread_barrier_destroy
+  SRCS
+    pthread_barrier_destroy.cpp
+  HDRS
+    pthread_barrier_destroy.h
+  DEPENDS
+    libc.include.pthread
+    libc.src.__support.threads.linux.barrier
+)
+
+add_entrypoint_object(
+  pthread_barrier_wait
+  SRCS
+    pthread_barrier_wait.cpp
+  HDRS
+    pthread_barrier_wait.h
+  DEPENDS
+    libc.include.pthread
+    libc.src.__support.threads.linux.barrier
+)
+
 add_entrypoint_object(
   pthread_mutex_init
   SRCS

libc/src/pthread/pthread_barrier_destroy.cpp

@@ -0,0 +1,22 @@
+//===-- Implementation of the pthread_barrier_destroy 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 "pthread_barrier_destroy.h"
+
+#include "hdr/types/pthread_barrier_t.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/threads/linux/barrier.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, pthread_barrier_destroy, (pthread_barrier_t * b)) {
+  return Barrier::destroy(reinterpret_cast<Barrier *>(b));
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/pthread/pthread_barrier_destroy.h

@@ -0,0 +1,21 @@
+//===-- Implementation header for pthread_barrier_destroy --------*- C++-*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_PTHREAD_PTHREAD_BARRIER_DESTROY_H
+#define LLVM_LIBC_SRC_PTHREAD_PTHREAD_BARRIER_DESTROY_H
+
+#include "hdr/types/pthread_barrier_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int pthread_barrier_destroy(pthread_barrier_t *b);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_PTHREAD_PTHREAD_BARRIER_DESTROY_H

libc/src/pthread/pthread_barrier_init.cpp

@@ -0,0 +1,26 @@
+//===-- Implementation of the pthread_barrier_init 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 "pthread_barrier_init.h"
+
+#include "hdr/types/pthread_barrier_t.h"
+#include "hdr/types/pthread_barrierattr_t.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/threads/linux/barrier.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, pthread_barrier_init,
+                   (pthread_barrier_t * b,
+                    const pthread_barrierattr_t *__restrict attr,
+                    unsigned count)) {
+  return Barrier::init(reinterpret_cast<Barrier *>(b), attr, count);
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/pthread/pthread_barrier_init.h

@@ -0,0 +1,24 @@
+//===-- Implementation header for pthread_barrier_init ----------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_PTHREAD_PTHREAD_BARRIER_INIT_H
+#define LLVM_LIBC_SRC_PTHREAD_PTHREAD_BARRIER_INIT_H
+
+#include "hdr/types/pthread_barrier_t.h"
+#include "hdr/types/pthread_barrierattr_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int pthread_barrier_init(pthread_barrier_t *b,
+                         const pthread_barrierattr_t *__restrict attr,
+                         unsigned count);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_PTHREAD_PTHREAD_BARRIER_INIT_H

libc/src/pthread/pthread_barrier_wait.cpp

@@ -0,0 +1,22 @@
+//===-- Implementation of the pthread_barrier_wait 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 "pthread_barrier_wait.h"
+
+#include "hdr/types/pthread_barrier_t.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/threads/linux/barrier.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, pthread_barrier_wait, (pthread_barrier_t * b)) {
+  return reinterpret_cast<Barrier *>(b)->wait();
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/pthread/pthread_barrier_wait.h

@@ -0,0 +1,21 @@
+//===-- Implementation header for pthread_barrier_wait ----------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_PTHREAD_PTHREAD_BARRIER_WAIT_H
+#define LLVM_LIBC_SRC_PTHREAD_PTHREAD_BARRIER_WAIT_H
+
+#include "hdr/types/pthread_barrier_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int pthread_barrier_wait(pthread_barrier_t *b);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_PTHREAD_PTHREAD_BARRIER_WAIT_H

libc/test/integration/src/pthread/CMakeLists.txt

@@ -18,6 +18,23 @@ add_integration_test(
     libc.src.pthread.pthread_join
 )
 
+add_integration_test(
+  pthread_barrier_test
+  SUITE
+    libc-pthread-integration-tests
+  SRCS
+    pthread_barrier_test.cpp
+  DEPENDS
+    libc.include.pthread
+    libc.src.errno.errno
+    libc.src.pthread.pthread_barrier_destroy
+    libc.src.pthread.pthread_barrier_wait
+    libc.src.pthread.pthread_barrier_init
+    libc.src.pthread.pthread_create
+    libc.src.pthread.pthread_join
+    libc.src.stdio.printf
+)
+
 add_integration_test(
   pthread_rwlock_test
   SUITE

libc/test/integration/src/pthread/pthread_barrier_test.cpp

@@ -0,0 +1,117 @@
+//===-- Tests for pthread_barrier_t ---------------------------------------===//
+//
+// 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 "src/pthread/pthread_barrier_destroy.h"
+#include "src/pthread/pthread_barrier_init.h"
+#include "src/pthread/pthread_barrier_wait.h"
+
+#include "src/__support/CPP/atomic.h"
+#include "src/pthread/pthread_create.h"
+#include "src/pthread/pthread_join.h"
+#include "src/pthread/pthread_mutex_destroy.h"
+#include "src/pthread/pthread_mutex_init.h"
+#include "src/pthread/pthread_mutex_lock.h"
+#include "src/pthread/pthread_mutex_unlock.h"
+#include "src/string/memset.h"
+
+#include "test/IntegrationTest/test.h"
+
+#include <pthread.h>
+
+pthread_barrier_t barrier;
+LIBC_NAMESPACE::cpp::Atomic<int> counter;
+
+void *increment_counter_and_wait(void *args) {
+  counter.fetch_add(1);
+  return reinterpret_cast<void *>(
+      LIBC_NAMESPACE::pthread_barrier_wait(&barrier));
+}
+
+void single_use_barrier_test(int num_threads) {
+  counter.set(0);
+  // create n - 1 ADDITIONAL threads since the current thread will also wait at
+  // the barrier
+  pthread_t threads[num_threads - 1];
+  LIBC_NAMESPACE::memset(&barrier, 0, sizeof(pthread_barrier_t));
+  ASSERT_EQ(
+      LIBC_NAMESPACE::pthread_barrier_init(&barrier, nullptr, num_threads), 0);
+
+  for (int i = 0; i < num_threads - 1; ++i)
+    LIBC_NAMESPACE::pthread_create(&threads[i], nullptr,
+                                   increment_counter_and_wait, nullptr);
+
+  uintptr_t return_val_sum =
+      reinterpret_cast<uintptr_t>(increment_counter_and_wait(nullptr));
+  ASSERT_EQ(counter.load(), num_threads);
+
+  // verify only one thread got the PTHREAD_BARRIER_SERIAL_THREAD return value
+  for (int i = 0; i < num_threads - 1; ++i) {
+    void *ret;
+    LIBC_NAMESPACE::pthread_join(threads[i], &ret);
+    if (reinterpret_cast<uintptr_t>(ret) ==
+        static_cast<uintptr_t>(PTHREAD_BARRIER_SERIAL_THREAD)) {
+      return_val_sum += reinterpret_cast<uintptr_t>(ret);
+    } else {
+      ASSERT_EQ(ret, 0);
+    }
+  }
+  ASSERT_EQ(return_val_sum,
+            static_cast<uintptr_t>(PTHREAD_BARRIER_SERIAL_THREAD));
+
+  LIBC_NAMESPACE::pthread_barrier_destroy(&barrier);
+}
+
+void reused_barrier_test() {
+  counter.set(0);
+  const int NUM_THREADS = 30;
+  const int REPEAT = 20;
+  pthread_t threads[NUM_THREADS - 1]; // subtract 1 for main thread
+  LIBC_NAMESPACE::memset(&barrier, 0, sizeof(pthread_barrier_t));
+  ASSERT_EQ(
+      LIBC_NAMESPACE::pthread_barrier_init(&barrier, nullptr, NUM_THREADS), 0);
+
+  for (int i = 0; i < REPEAT; ++i) {
+    for (int j = 0; j < NUM_THREADS - 1; ++j)
+      LIBC_NAMESPACE::pthread_create(&threads[j], nullptr,
+                                     increment_counter_and_wait, nullptr);
+
+    uintptr_t return_val_sum =
+        reinterpret_cast<uintptr_t>(increment_counter_and_wait(nullptr));
+    ASSERT_EQ(counter.load(), NUM_THREADS * (i + 1));
+
+    // verify only one thread got the PTHREAD_BARRIER_SERIAL_THREAD return value
+    for (int i = 0; i < NUM_THREADS - 1; ++i) {
+      void *ret;
+      LIBC_NAMESPACE::pthread_join(threads[i], &ret);
+      if (reinterpret_cast<uintptr_t>(ret) ==
+          static_cast<uintptr_t>(PTHREAD_BARRIER_SERIAL_THREAD)) {
+        return_val_sum += reinterpret_cast<uintptr_t>(ret);
+      } else {
+        ASSERT_EQ(ret, 0);
+      }
+    }
+    ASSERT_EQ(return_val_sum,
+              static_cast<uintptr_t>(PTHREAD_BARRIER_SERIAL_THREAD));
+  }
+
+  LIBC_NAMESPACE::pthread_barrier_destroy(&barrier);
+}
+
+void *barrier_wait(void *in) {
+  return reinterpret_cast<void *>(
+      LIBC_NAMESPACE::pthread_barrier_wait(&barrier));
+}
+
+TEST_MAIN() {
+  // don't create any additional threads; only use main thread
+  single_use_barrier_test(1);
+
+  single_use_barrier_test(30);
+  reused_barrier_test();
+  return 0;
+}