latch: add simple latch based on a mutex and cv

1 files changed, 41 insertions, 0 deletions

diff --git a/latch.h b/latch.h
new file mode 100644
index 0000000..ec2006e
--- /dev/null
+++ b/latch.h
@@ -0,0 +1,41 @@
+#ifndef UTILS_TIMER_H
+#define UTILS_TIMER_H
+
+#include <condition_variable>
+#include <mutex>
+
+#include <cassert>
+
+/// latch
+///
+/// A simple one-shot latch based on a mutex and condition variable.
+///
+/// The latch is initialized with a number N of threads to wait for. Different
+/// threads can call arrive_and_wait() on the latch. Those threads enter a wait
+/// state until the Nth thread calls arrive_and_wait(), which then releases all
+/// threads at the same time.
+struct latch {
+  explicit latch(std::size_t cnt) : m_cnt{cnt} {}
+  ~latch() {
+    assert(m_cnt == 0);
+  }
+
+  void arrive_and_wait() {
+    std::unique_lock<std::mutex> lk(m_mtx);
+    m_cnt -= 1;
+
+    if (m_cnt != 0) {
+      m_cv.wait(lk, [this]() { return m_cnt == 0; });
+    } else {
+      m_cv.notify_all();
+    }
+  }
+
+ private:
+  std::size_t m_cnt;
+
+  std::mutex m_mtx;
+  std::condition_variable m_cv;
+};
+
+#endif