From c68694163b20b475710d0c1b61d8ae3a79a992fd Mon Sep 17 00:00:00 2001
From: Rainer Kartmann <rainer.kartmann@kit.edu>
Date: Mon, 7 Dec 2020 14:18:01 +0100
Subject: [PATCH] Add CountingSemaphore
---
SimoxUtility/CMakeLists.txt | 2 +
SimoxUtility/threads.h | 1 +
SimoxUtility/threads/CountingSemaphore.cpp | 42 +++++++++++++++
SimoxUtility/threads/CountingSemaphore.h | 61 ++++++++++++++++++++++
4 files changed, 106 insertions(+)
create mode 100644 SimoxUtility/threads/CountingSemaphore.cpp
create mode 100644 SimoxUtility/threads/CountingSemaphore.h
diff --git a/SimoxUtility/CMakeLists.txt b/SimoxUtility/CMakeLists.txt
index 02e16fe9d..2745556a2 100644
--- a/SimoxUtility/CMakeLists.txt
+++ b/SimoxUtility/CMakeLists.txt
@@ -88,6 +88,7 @@ SET(SOURCES
shapes/json_conversions.cpp
threads/system_thread_id.cpp
+ threads/CountingSemaphore.cpp
)
SET(INCLUDES
@@ -256,6 +257,7 @@ SET(INCLUDES
backport/span/gcc_header.h
threads/system_thread_id.h
+ threads/CountingSemaphore.h
)
simox_generate_subdir_headers(
diff --git a/SimoxUtility/threads.h b/SimoxUtility/threads.h
index cd685bff0..7c9962102 100644
--- a/SimoxUtility/threads.h
+++ b/SimoxUtility/threads.h
@@ -2,4 +2,5 @@
// This file is generated!
+#include "threads/CountingSemaphore.h"
#include "threads/system_thread_id.h"
diff --git a/SimoxUtility/threads/CountingSemaphore.cpp b/SimoxUtility/threads/CountingSemaphore.cpp
new file mode 100644
index 000000000..9e6687e62
--- /dev/null
+++ b/SimoxUtility/threads/CountingSemaphore.cpp
@@ -0,0 +1,42 @@
+#include "CountingSemaphore.h"
+
+
+namespace simox::threads
+{
+
+ CountingSemaphore::CountingSemaphore()
+ {}
+
+ CountingSemaphore::CountingSemaphore(unsigned int count) : _count(count)
+ {}
+
+
+ void CountingSemaphore::notify()
+ {
+ std::lock_guard<std::mutex> lock(_mutex);
+ ++_count;
+ _condition.notify_one();
+ }
+
+ void CountingSemaphore::wait()
+ {
+ std::unique_lock<std::mutex> lock(_mutex);
+ _condition.wait(lock, [this]()
+ {
+ return _count > 0;
+ });
+ --_count;
+ }
+
+ bool CountingSemaphore::try_wait()
+ {
+ std::unique_lock<std::mutex> lock(_mutex);
+ if (_count > 0)
+ {
+ --_count;
+ return true;
+ }
+ return false;
+ }
+
+}
diff --git a/SimoxUtility/threads/CountingSemaphore.h b/SimoxUtility/threads/CountingSemaphore.h
new file mode 100644
index 000000000..a7bc78f90
--- /dev/null
+++ b/SimoxUtility/threads/CountingSemaphore.h
@@ -0,0 +1,61 @@
+#pragma once
+
+#include <condition_variable>
+#include <mutex>
+
+
+namespace simox::threads
+{
+
+ /**
+ * @brief A counting semaphore.
+ *
+ * Threads can enter when the internal count is > 0.
+ * Notifiying the semaphore increments the count and allows threads to enter.
+ * A thread can wait until it may enter. When it enters, it decrements
+ * the internal count.
+ *
+ * Can be used e.g. in a Producer-Consumer pattern.
+ * The producer signals new jobs via `notify()`, while the consumer waits
+ * for new jobs via `wait()`.
+ */
+ class CountingSemaphore
+ {
+ public:
+
+ /// Construct an initially blocking semaphore (initial count 0).
+ CountingSemaphore();
+ /// Construct a semaphore with the given count.
+ CountingSemaphore(unsigned int count);
+
+ /**
+ * @brief Signal that one waiting thread may continue.
+ * Also known as `post()` or `signal()`.
+ */
+ void notify();
+
+ /**
+ * @brief Wait until a thread may enter.
+ */
+ void wait();
+
+ /**
+ * @brief Try to enter. If the semaphore is currently blocking, return false.
+ * @return True if entering was successful, false if semaphore was blocking.
+ */
+ bool try_wait();
+
+
+ private:
+
+ /// The mutex for _condition and _count.
+ std::mutex _mutex;
+ /// The condition variable to wake up waking threads.
+ std::condition_variable _condition;
+
+ /// The current count. Waiting threads may enter when > 0.
+ unsigned int _count = 0;
+
+ };
+
+}
--
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