4 files changed, 165 insertions, 1 deletions
diff --git a/works/life/operating-system-experiment/CMakeLists.txt b/works/life/operating-system-experiment/CMakeLists.txt
index 8b4617f..c8afc24 100644
--- a/works/life/operating-system-experiment/CMakeLists.txt
+++ b/works/life/operating-system-experiment/CMakeLists.txt
@@ -9,7 +9,7 @@ set(CMAKE_CXX_STANDARD 17)
 
 find_package(fmt CONFIG REQUIRED)
 find_package(Microsoft.GSL CONFIG REQUIRED)
-add_library(cru_system SHARED Thread.cpp Mutex.cpp Interlocked.cpp)
+add_library(cru_system SHARED Thread.cpp Mutex.cpp Interlocked.cpp Semaphore.cpp)
 target_link_libraries(cru_system PUBLIC Microsoft.GSL::GSL fmt::fmt)
 target_compile_definitions(cru_system PUBLIC CRU_EXPORT_API)
 if(UNIX)
@@ -27,3 +27,7 @@ target_link_libraries(mutex_avoid_data_race_demo PRIVATE cru_system)
 
 add_executable(interlocked_avoid_data_race_demo InterlockedAvoidDataRaceDemo.cpp)
 target_link_libraries(interlocked_avoid_data_race_demo PRIVATE cru_system)
+
+add_executable(semaphore_avoid_data_race_demo SemaphoreAvoidDataRaceDemo.cpp)
+target_link_libraries(semaphore_avoid_data_race_demo PRIVATE cru_system)
+
diff --git a/works/life/operating-system-experiment/Semaphore.cpp b/works/life/operating-system-experiment/Semaphore.cpp
new file mode 100644
index 0000000..e8221fd
--- /dev/null
+++ b/works/life/operating-system-experiment/Semaphore.cpp
@@ -0,0 +1,78 @@
+#include "Semaphore.h"
+
+#include <cassert>
+
+#ifndef CRU_WINDOWS
+#include <errno.h>
+#endif
+
+namespace cru {
+Semaphore::Semaphore(unsigned init_value) {
+#ifdef CRU_WINDOWS
+#else
+  semaphore_ = std::make_unique<sem_t>();
+  auto c = sem_init(semaphore_.get(), 0, init_value);
+  assert(c == 0);
+#endif
+}
+
+Semaphore::Semaphore(Semaphore &&other)
+#ifdef CRU_WINDOWS
+#else
+    : semaphore_(std::move(other.semaphore_))
+#endif
+{
+}
+
+Semaphore &Semaphore::operator=(Semaphore &&other) {
+  if (this != &other) {
+    Destroy();
+#ifdef CRU_WINDOWS
+#else
+    semaphore_ = std::move(other.semaphore_);
+#endif
+  }
+  return *this;
+}
+
+Semaphore::~Semaphore() { Destroy(); }
+
+void Semaphore::P() { Acquire(); }
+void Semaphore::V() { Release(); }
+
+void Semaphore::Acquire() {
+#ifdef CRU_WINDOWS
+#else
+  auto c = sem_wait(semaphore_.get());
+  assert(c == 0);
+#endif
+}
+
+bool Semaphore::TryAcquire() {
+#ifdef CRU_WINDOWS
+#else
+  auto c = sem_trywait(semaphore_.get());
+  assert((c == 0) || (c == -1 && errno == EAGAIN));
+  return c == 0 ? true : false;
+#endif
+}
+
+void Semaphore::Release() {
+#ifdef CRU_WINDOWS
+#else
+  auto c = sem_post(semaphore_.get());
+  assert(c == 0);
+#endif
+}
+
+void Semaphore::Destroy() {
+#ifdef CRU_WINDOWS
+#else
+  if (semaphore_ != nullptr) {
+    auto c = sem_destroy(semaphore_.get());
+    assert(c == 0);
+    semaphore_ = nullptr;
+  }
+#endif
+}
+} // namespace cru
+\ No newline at end of file
diff --git a/works/life/operating-system-experiment/Semaphore.h b/works/life/operating-system-experiment/Semaphore.h
new file mode 100644
index 0000000..1d49b60
--- /dev/null
+++ b/works/life/operating-system-experiment/Semaphore.h
@@ -0,0 +1,46 @@
+#ifndef HEADER_SEMAPHORE_H
+#define HEADER_SEMAPHORE_H
+
+#include "Base.h"
+
+#include <memory>
+
+#ifdef CRU_WINDOWS
+#include <Windows.h>
+#else
+#include <semaphore.h>
+#endif
+
+namespace cru {
+class CRU_API Semaphore {
+public:
+  explicit Semaphore(unsigned init_value = 1);
+
+  Semaphore(const Semaphore &other) = delete;
+  Semaphore &operator=(const Semaphore &other) = delete;
+
+  Semaphore(Semaphore &&other);
+  Semaphore &operator=(Semaphore &&other);
+
+  ~Semaphore();
+
+public:
+  void P();
+  void V();
+
+  void Acquire();
+  bool TryAcquire();
+  void Release();
+
+private:
+  void Destroy();
+
+private:
+#ifdef CRU_WINDOWS
+#else
+  std::unique_ptr<sem_t> semaphore_;
+#endif
+};
+} // namespace cru
+
+#endif
+\ No newline at end of file
diff --git a/works/life/operating-system-experiment/SemaphoreAvoidDataRaceDemo.cpp b/works/life/operating-system-experiment/SemaphoreAvoidDataRaceDemo.cpp
new file mode 100644
index 0000000..0068082
--- /dev/null
+++ b/works/life/operating-system-experiment/SemaphoreAvoidDataRaceDemo.cpp
@@ -0,0 +1,36 @@
+#include "Semaphore.h"
+#include "Thread.h"
+
+#include <iostream>
+
+int main() {
+  unsigned data = 0;
+
+  cru::Semaphore semaphore;
+
+  cru::Thread t1([&data, &semaphore] {
+    for (int i = 0; i < 100000; i++) {
+      semaphore.P();
+      data += 10;
+      semaphore.V();
+    }
+  });
+
+  cru::Thread t2([&data, &semaphore] {
+    for (int i = 0; i < 100000; i++) {
+      semaphore.P();
+      data += 10;
+      semaphore.V();
+    }
+  });
+
+  std::cout << "Created thread: " << t1.GetNativeID() << '\n';
+  std::cout << "Created thread: " << t2.GetNativeID() << '\n';
+
+  t1.Join();
+  t2.Join();
+  std::cout << "Answer is " << data << ", which is "
+            << (data == 2000000 ? "correct" : "false") << '\n';
+
+  return 0;
+}