From 3a122c7c1a08bff6cbff5b81f357c5c6efaad84d Mon Sep 17 00:00:00 2001
From: Brian Norris <banorris@uci.edu>
Date: Tue, 4 Dec 2012 16:54:04 -0800
Subject: [PATCH] dekker-fences: add Dekker's critical section algorithm

Now that we support fences, add a test benchmark that uses fences. This
one just uses seq-cst fences.

Downloaded from:

   http://www.justsoftwaresolutions.co.uk/threading/

Modified to avoid static construction. i.e., change:
  std::atomic<int> turn(0);
to
  std::atomic<int> turn;
  ...
  turn = 0;
And added user_main() method to launch the two threads.
---
 dekker-fences/.gitignore       |  1 +
 dekker-fences/Makefile         | 11 +++++
 dekker-fences/dekker-fences.cc | 87 ++++++++++++++++++++++++++++++++++
 3 files changed, 99 insertions(+)
 create mode 100644 dekker-fences/.gitignore
 create mode 100644 dekker-fences/Makefile
 create mode 100644 dekker-fences/dekker-fences.cc

diff --git a/dekker-fences/.gitignore b/dekker-fences/.gitignore
new file mode 100644
index 0000000..560aebf
--- /dev/null
+++ b/dekker-fences/.gitignore
@@ -0,0 +1 @@
+/dekker-fences
diff --git a/dekker-fences/Makefile b/dekker-fences/Makefile
new file mode 100644
index 0000000..1996599
--- /dev/null
+++ b/dekker-fences/Makefile
@@ -0,0 +1,11 @@
+include ../benchmarks.mk
+
+TESTNAME = dekker-fences
+
+all: $(TESTNAME)
+
+$(TESTNAME): $(TESTNAME).cc
+	$(CXX) -o $@ $< $(CPPFLAGS) $(LDFLAGS)
+
+clean:
+	rm -f $(TESTNAME) *.o
diff --git a/dekker-fences/dekker-fences.cc b/dekker-fences/dekker-fences.cc
new file mode 100644
index 0000000..81f6098
--- /dev/null
+++ b/dekker-fences/dekker-fences.cc
@@ -0,0 +1,87 @@
+/*
+ * Dekker's critical section algorithm, implemented with fences.
+ *
+ * URL:
+ *   http://www.justsoftwaresolutions.co.uk/threading/
+ */
+
+#include <atomic>
+#include <threads.h>
+
+#include "librace.h"
+
+std::atomic<bool> flag0, flag1;
+std::atomic<int> turn;
+
+uint32_t var = 0;
+
+void p0(void *arg)
+{
+	flag0.store(true,std::memory_order_relaxed);
+	std::atomic_thread_fence(std::memory_order_seq_cst);
+
+	while (flag1.load(std::memory_order_relaxed))
+	{
+		if (turn.load(std::memory_order_relaxed) != 0)
+		{
+			flag0.store(false,std::memory_order_relaxed);
+			while (turn.load(std::memory_order_relaxed) != 0)
+			{
+			}
+			flag0.store(true,std::memory_order_relaxed);
+			std::atomic_thread_fence(std::memory_order_seq_cst);
+		}
+	}
+	std::atomic_thread_fence(std::memory_order_acquire);
+
+	// critical section
+	store_32(&var, 1);
+
+	turn.store(1,std::memory_order_relaxed);
+	std::atomic_thread_fence(std::memory_order_release);
+	flag0.store(false,std::memory_order_relaxed);
+}
+
+void p1(void *arg)
+{
+	flag1.store(true,std::memory_order_relaxed);
+	std::atomic_thread_fence(std::memory_order_seq_cst);
+
+	while (flag0.load(std::memory_order_relaxed))
+	{
+		if (turn.load(std::memory_order_relaxed) != 1)
+		{
+			flag1.store(false,std::memory_order_relaxed);
+			while (turn.load(std::memory_order_relaxed) != 1)
+			{
+			}
+			flag1.store(true,std::memory_order_relaxed);
+			std::atomic_thread_fence(std::memory_order_seq_cst);
+		}
+	}
+	std::atomic_thread_fence(std::memory_order_acquire);
+
+	// critical section
+	store_32(&var, 2);
+
+	turn.store(0,std::memory_order_relaxed);
+	std::atomic_thread_fence(std::memory_order_release);
+	flag1.store(false,std::memory_order_relaxed);
+}
+
+int user_main(int argc, char **argv)
+{
+	thrd_t a, b;
+
+	flag0 = false;
+	flag1 = false;
+	turn = 0;
+
+	thrd_create(&a, p0, NULL);
+	thrd_create(&b, p1, NULL);
+
+	thrd_join(a);
+	thrd_join(b);
+
+	return 0;
+}
-- 
2.34.1