Add thread-based RCU

Add the Linux Kernel style thread-based simple RCU.
It supports sparse checking[1].

thread-rcu target to use Linux Kernel Memory Model (LKMM).
C11 memory model may no compatible to LKMM.
Check the paper[2] to see more detail.

[1] https://www.kernel.org/doc/html/latest/dev-tools/sparse.html
[2] http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0124r6.html

Author: linD026

README.md

@@ -30,6 +30,7 @@ purpose of these programs is to be illustrative and educational.
     - [qsbr](qsbr/): An implementation of Quiescent state based reclamation (QSBR).
     - [list-move](list-move/): Evaluation of two concurrent linked lists: QSBR and lock-based.
     - [rcu\_queue](rcu_queue/): An efficient concurrent queue based on QSBR.
+    - [thread-rcu](thread-rcu/): A Linux Kernel style thread-based simple RCU.
 * Applications
     - [httpd](httpd/): A multi-threaded web server.
     - [map-reduce](map-reduce/): word counting using MapReduce.

thread-rcu/Makefile

@@ -0,0 +1,30 @@
+CFLAGS = -Wall
+CFLAGS += -g
+CFLAGS += -std=c11
+CFLAGS += -D'N_READERS=10'
+CFLAGS += -fsanitize=thread
+LDFLAGS += -lpthread
+
+# The pthread mutex initializer will warning:
+# thrd_rcu.h:95:42: warning: Using plain integer as NULL pointer
+# We can ignore it.
+SPARSE_FLAGS = -Wno-non-pointer-null
+
+main: main.c
+	$(CC) -o $@ $< $(CFLAGS) $(LDFLAGS)
+
+clang: CC=clang
+clang: main
+
+all: main
+
+# Semantic Checker
+# https://www.kernel.org/doc/html/latest/dev-tools/sparse.html
+sparse:
+	sparse main.c $(CFLAGS) $(SPARSE_FLAGS)
+
+indent:
+	clang-format -i *.[ch]
+
+clean:
+	rm -f main

thread-rcu/main.c

@@ -0,0 +1,74 @@
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "rcu.h"
+
+struct test {
+    unsigned int count;
+};
+
+static struct test __rcu *dut;
+
+static void *reader_func(void *argv)
+{
+    struct test *tmp;
+
+    if (rcu_init())
+        abort();
+
+    rcu_read_lock();
+
+    tmp = rcu_dereference(dut);
+
+    printf("[reader #%u] %u\n", current_tid(), tmp->count);
+
+    rcu_read_unlock();
+
+    pthread_exit(NULL);
+}
+
+static void *updater_func(void *argv)
+{
+    struct test *oldp;
+    struct test *newval = malloc(sizeof(struct test));
+
+    newval->count = current_tid();
+
+    printf("[updater #%u]\n", newval->count);
+
+    oldp = rcu_assign_pointer(dut, newval);
+
+    synchronize_rcu();
+    free(oldp);
+
+    pthread_exit(NULL);
+}
+
+int main(int argc, char *argv[])
+{
+    pthread_t reader[N_READERS];
+    pthread_t updater;
+    int i;
+
+    dut = (struct test __rcu *) malloc(sizeof(struct test));
+    rcu_uncheck(dut)->count = 0;
+
+    for (i = 0; i < N_READERS / 2; i++)
+        pthread_create(&reader[i], NULL, reader_func, NULL);
+
+    pthread_create(&updater, NULL, updater_func, NULL);
+
+    for (i = N_READERS / 2; i < N_READERS; i++)
+        pthread_create(&reader[i], NULL, reader_func, NULL);
+
+    for (i = 0; i < N_READERS; i++)
+        pthread_join(reader[i], NULL);
+
+    pthread_join(updater, NULL);
+
+    free(rcu_uncheck(dut));
+    rcu_clean();
+
+    return 0;
+}