Implement the basic operations on sem_t

Summary: This means that Windows builds no longer require pthreads in order to run tests. (previously we were relying on the pthreads implementation we were using to provide semaphore.h for us)

Reviewed By: yfeldblum

Differential Revision: D9568125

fbshipit-source-id: 712f542c9a29627f72b41e1def2b79d591a33317

folly/portability/Semaphore.cpp

+/*
+ * Copyright 2012-present Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <folly/portability/Semaphore.h>
+
+#include <folly/portability/Windows.h>
+
+#include <errno.h>
+#include <mutex>
+
+#if _WIN32
+namespace folly::portability::semaphore {
+struct sem_t_ {
+  std::mutex mtx{};
+  HANDLE sema{INVALID_HANDLE_VALUE};
+  int32_t value{0};
+};
+
+int sem_init(sem_t* s, int shared, unsigned int value) {
+  // Don't support cross-process shared semaphores.
+  if (shared != 0) {
+    return -1;
+  }
+  auto sem = CreateSemaphoreA(nullptr, 0, SEM_VALUE_MAX, nullptr);
+  if (sem == 0) {
+    return -1;
+  }
+  auto ret = new sem_t_();
+  ret->sema = sem;
+  ret->value = value;
+  *s = ret;
+  return 0;
+}
+
+int sem_destroy(sem_t* s) {
+  if (!CloseHandle((*s)->sema)) {
+    return -1;
+  }
+  delete *s;
+  *s = nullptr;
+  return 0;
+}
+
+int sem_post(sem_t* s) {
+  std::lock_guard<std::mutex> lock{(*s)->mtx};
+  if ((*s)->value < SEM_VALUE_MAX) {
+    if (++(*s)->value <= 0 && !ReleaseSemaphore((*s)->sema, 1, nullptr)) {
+      --(*s)->value;
+      errno = EINVAL;
+      return -1;
+    }
+  } else {
+    errno = ERANGE;
+    return -1;
+  }
+  return 0;
+}
+
+int sem_trywait(sem_t* s) {
+  std::lock_guard<std::mutex> lock{(*s)->mtx};
+  if ((*s)->value > 0) {
+    (*s)->value--;
+    return 0;
+  } else {
+    errno = EAGAIN;
+    return -1;
+  }
+}
+
+int sem_wait(sem_t* s) {
+  int32_t value = 0;
+  {
+    std::lock_guard<std::mutex> lock{(*s)->mtx};
+    value = --(*s)->value;
+  }
+
+  if (value < 0) {
+    if (WaitForSingleObject((*s)->sema, INFINITE) != WAIT_OBJECT_0) {
+      errno = EINVAL;
+      return -1;
+    }
+  }
+  return 0;
+}
+} // namespace folly::portability::semaphore
+#endif

folly/portability/Semaphore.h

@@ -16,9 +16,20 @@
 
 #pragma once
 
-// On Windows, the include order matters, as the pthread implementation we
-// support attempts to use a different definition of `mode_t` than everything
-// else, so we have to make sure our definition of it is first.
-#include <folly/portability/SysTypes.h>
-
+#ifndef _WIN32
 #include <semaphore.h>
+#else
+#include <limits.h>
+
+#define SEM_VALUE_MAX INT_MAX
+namespace folly::portability::semaphore {
+using sem_t = struct sem_t_*;
+int sem_init(sem_t* s, int shared, unsigned int value);
+int sem_destroy(sem_t* s);
+int sem_post(sem_t* s);
+int sem_trywait(sem_t* s);
+int sem_wait(sem_t* s);
+} // namespace folly::portability::semaphore
+
+/* using override */ using namespace folly::portability::semaphore;
+#endif