[libc] Implement barriers for pthreads

libc/config/linux/x86_64/entrypoints.txt

@@ -1039,6 +1039,9 @@ 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/include/CMakeLists.txt

@@ -390,6 +390,8 @@ 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

@@ -53,6 +53,8 @@ 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)
+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/pthread_barrier_t.h

@@ -0,0 +1,16 @@
+//===-- 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
+
+typedef struct {
+  char padding[88];
+} 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/CMakeLists.txt

@@ -90,6 +90,17 @@ if(TARGET libc.src.__support.threads.${LIBC_TARGET_OS}.CndVar)
   )
 endif()
 
+add_object_library(
+  barrier
+  HDRS
+    barrier.h
+  SRCS
+    barrier.cpp
+  DEPENDS
+    .CndVar
+    .mutex
+)
+
 if (LLVM_LIBC_FULL_BUILD)
   set(identifier_dependency_on_thread libc.src.__support.threads.thread)
 endif()

libc/src/__support/threads/barrier.cpp

@@ -0,0 +1,83 @@
+//===-- 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/barrier.h"
+#include "barrier.h"
+#include "hdr/errno_macros.h"
+#include "src/__support/threads/mutex.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+const int BARRIER_FIRST_EXITED = -1;
+
+int Barrier::init(Barrier *b,
+                  const pthread_barrierattr_t *attr __attribute__((unused)),
+                  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;
+
+  Mutex::init(&b->m, false, false, false, false);
+  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) {
+    // this is the last thread to call wait(), so lets wake everyone up
+    blocking = false;
+    exiting.broadcast();
+  } else {
+    // block threads until waiting = expected
+    while (blocking) {
+      exiting.wait(&m);
+    }
+  }
+  waiting--;
+
+  // all threads have exited the barrier, lets let the ones waiting to enter
+  // continue
+  if (waiting == 0) {
+    blocking = true;
+    entering.broadcast();
+    m.unlock();
+    return BARRIER_FIRST_EXITED;
+  }
+  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/barrier.h

@@ -0,0 +1,44 @@
+//===-- 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 "include/llvm-libc-types/pthread_barrier_t.h"
+#include "include/llvm-libc-types/pthread_barrierattr_t.h"
+#include "src/__support/macros/config.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
+
+extern const int BARRIER_FIRST_EXITED;
+
+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();
+};
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC___SUPPORT_SRC_THREADS_LINUX_BARRIER_H

libc/src/pthread/CMakeLists.txt

@@ -271,6 +271,40 @@ 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.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.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.barrier
+)
+
 add_entrypoint_object(
   pthread_mutex_init
   SRCS

libc/src/pthread/pthread_barrier_destroy.cpp

@@ -0,0 +1,23 @@
+//===-- Linux 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_destroy.h"
+
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/threads/barrier.h"
+
+#include <pthread.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 "src/__support/macros/config.h"
+#include <pthread.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 +1,31 @@
+//===-- Linux 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 "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/threads/barrier.h"
+
+#include <pthread.h>
+
+namespace LIBC_NAMESPACE_DECL {
+
+static_assert(
+    sizeof(Barrier) <= sizeof(pthread_barrier_t),
+    "The public pthread_barrier_t type cannot accommodate the internal "
+    "barrier type.");
+
+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 +1,23 @@
+//===-- 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 "src/__support/macros/config.h"
+#include <pthread.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