Add thread-based RCU

[linD026]

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

With sparse, it will report:

main.c: note: in included file:
thrd_rcu.h:95:42: warning: Using plain integer as NULL pointer
thrd_rcu.h:95:42: warning: Using plain integer as NULL pointer

It is from the pthread_mutex_t initializer, we can ignore it.

[1] https://www.kernel.org/doc/html/latest/dev-tools/sparse.html

---

From the ThreadSanitizer report, ignore the volatile type data race warning [1][2],
there still have the data race warning.

[reader 2835343104] 0
[reader 2826950400] 0
[reader 2818557696] 0
[reader 2810164992] 0
[reader 2801772288] 0
[updater 2793379584]
==================
WARNING: ThreadSanitizer: data race (pid=434539)
  Write of size 8 at 0x7b0400000000 by thread T6:
    #0 free ../../../../src/libsanitizer/tsan/tsan_interceptors_posix.cpp:711 (libtsan.so.0+0x37ab8)
    #1 updater_side /home/xxxx/linux2021/concurrent-programs/thrd_rcu/main.c:41 (main+0x1a38)

  Previous read of size 4 at 0x7b0400000000 by thread T5:
    #0 reader_side /home/xxxx/linux2021/concurrent-programs/thrd_rcu/main.c:23 (main+0x1898)

  Thread T6 (tid=434546, running) created by main thread at:
    #0 pthread_create ../../../../src/libsanitizer/tsan/tsan_interceptors_posix.cpp:969 (libtsan.so.0+0x605f8)
    #1 main /home/xxxx/linux2021/concurrent-programs/thrd_rcu/main.c:59 (main+0x1429)

  Thread T5 (tid=434545, finished) created by main thread at:
    #0 pthread_create ../../../../src/libsanitizer/tsan/tsan_interceptors_posix.cpp:969 (libtsan.so.0+0x605f8)
    #1 main /home/xxxx/linux2021/concurrent-programs/thrd_rcu/main.c:56 (main+0x13fd)

SUMMARY: ThreadSanitizer: data race /home/xxxx/linux2021/concurrent-programs/thrd_rcu/main.c:41 in updater_side
==================
[reader 2784986880] 2793379584
[reader 2744121088] 2793379584
[reader 2735728384] 2793379584
[reader 2727335680] 2793379584
[reader 2718942976] 2793379584
ThreadSanitizer: reported 1 warnings

I try to debug it, but cannot figure out where the wrong is.
Not sure if it is a false positive or not.

[1] https://gcc.gnu.org/pipermail/gcc-patches/2020-June/547633.html
[2] https://gcc.gnu.org/gcc-11/changes.html

[jserv]

Rename the directory to "thread-rcu" and update README.md for high level description.

[linD026]

I change to C11 ( -std=c11 ), now the atomic operation and memory barrier are using stdatomic.h.
And the memory model is also tried to be compatible with C11.

---

But, there are still warnings:

[reader 801105664] 0
[reader 792712960] 0
[reader 784320256] 0
[reader 775927552] 0
[reader 767534848] 0
[updater 759142144]
==================
WARNING: ThreadSanitizer: data race (pid=477342)
  Write of size 8 at 0x7b0400000000 by thread T6:
    #0 free ../../../../src/libsanitizer/tsan/tsan_interceptors_posix.cpp:711 (libtsan.so.0+0x37ab8)
    #1 updater_side /home/xxxx/linux2021/concurrent-programs/thread-rcu/main.c:43 (main+0x1d5f)

  Previous read of size 4 at 0x7b0400000000 by thread T5:
    #0 reader_side /home/xxxx/linux2021/concurrent-programs/thread-rcu/main.c:24 (main+0x1c32)

  Thread T6 (tid=477349, running) created by main thread at:
    #0 pthread_create ../../../../src/libsanitizer/tsan/tsan_interceptors_posix.cpp:969 (libtsan.so.0+0x605f8)
    #1 main /home/xxxx/linux2021/concurrent-programs/thread-rcu/main.c:60 (main+0x1e3f)

  Thread T5 (tid=477348, finished) created by main thread at:
    #0 pthread_create ../../../../src/libsanitizer/tsan/tsan_interceptors_posix.cpp:969 (libtsan.so.0+0x605f8)
    #1 main /home/xxxx/linux2021/concurrent-programs/thread-rcu/main.c:58 (main+0x1e18)

SUMMARY: ThreadSanitizer: data race /home/xxxx/linux2021/concurrent-programs/thread-rcu/main.c:43 in updater_side
==================
[reader 750749440] 759142144
[reader 711980800] 759142144
[reader 703588096] 759142144
[reader 695195392] 759142144
[reader 686802688] 759142144
ThreadSanitizer: reported 1 warnings

[jserv]

The program is not built with clang (version 10) because of various errors:

address argument to atomic operation must be a pointer to _Atomic type

[linD026]

It still has the warnings from ThreadSanitizer.

---

I combine the rcu_nesting with the next pointer (at the lowest 2 bit).
And make some changes to WRITE_ONCE() and READ_ONCE() to let the bitwise operation work.

But this kind of change will raise the warning from sparse.

sparse main.c -Wall -g -std=c11 -D'N_READERS=10' -fsanitize=thread -lpthread
main.c: note: in included file:
rcu.h:146:11: warning: Using plain integer as NULL pointer
rcu.h:146:11: warning: Using plain integer as NULL pointer
main.c:22:11: warning: incorrect type in argument 2 (different modifiers)
main.c:22:11:    expected void *
main.c:22:11:    got struct test [noderef] __rcu *volatile [atomic] *
main.c:40:12: warning: incorrect type in argument 2 (different modifiers)
main.c:40:12:    expected void *
main.c:40:12:    got struct test [noderef] __rcu *volatile [atomic] *
main.c:40:12: warning: incorrect type in argument 3 (different modifiers)
main.c:40:12:    expected void *
main.c:40:12:    got struct test [noderef] __rcu *volatile [atomic] *
rcu.h:167:12: warning: incorrect type in argument 2 (different modifiers)
rcu.h:167:12:    expected void *
rcu.h:167:12:    got struct rcu_node *volatile [atomic] *
rcu.h:168:13: warning: incorrect type in argument 2 (different modifiers)
rcu.h:168:13:    expected void *
rcu.h:168:13:    got struct rcu_node *volatile [atomic] *
rcu.h:173:42: warning: incorrect type in argument 2 (different modifiers)
rcu.h:173:42:    expected void *
rcu.h:173:42:    got struct rcu_node *volatile [atomic] *
rcu.h:223:5: warning: incorrect type in argument 2 (different modifiers)
rcu.h:223:5:    expected void *
rcu.h:223:5:    got unsigned long volatile [atomic] *
rcu.h:223:5: warning: incorrect type in argument 2 (different modifiers)
rcu.h:223:5:    expected void *
rcu.h:223:5:    got unsigned int volatile [atomic] *
rcu.h:223:5: warning: incorrect type in argument 2 (different modifiers)
rcu.h:223:5:    expected void *
rcu.h:223:5:    got unsigned long volatile [atomic] *
rcu.h:228:5: warning: incorrect type in argument 2 (different modifiers)
rcu.h:228:5:    expected void *
rcu.h:228:5:    got unsigned long volatile [atomic] *
rcu.h:228:5: warning: incorrect type in argument 2 (different modifiers)
rcu.h:228:5:    expected void *
rcu.h:228:5:    got unsigned long volatile [atomic] *
rcu.h:248:16: warning: incorrect type in argument 2 (different modifiers)
rcu.h:248:16:    expected void *
rcu.h:248:16:    got unsigned long volatile [atomic] *
rcu.h:247:45: warning: incorrect type in argument 2 (different modifiers)
rcu.h:247:45:    expected void *
rcu.h:247:45:    got unsigned long volatile [atomic] *
rcu.h:267:16: warning: incorrect type in argument 2 (different modifiers)
rcu.h:267:16:    expected void *
rcu.h:267:16:    got unsigned long volatile [atomic] *
rcu.h:266:45: warning: incorrect type in argument 2 (different modifiers)
rcu.h:266:45:    expected void *
rcu.h:266:45:    got unsigned long volatile [atomic] *

---

I will fix it a few days later since I have other stuff need to be done.
:(

[linD026]

Now, the ThreadSanitizer will not warn.
Sparse also not warn at ArchLinux v5.16.
But, it still warning on Ubuntu.

[linD026]

I fix up the warning raised by sparse.
It finally works well, now.

[linD026]

I attempted to build thread-rcu on Apple M1 running macOS 12.3, and the compiler complained:

cc -o main main.c -Wall -g -std=c11 -D'N_READERS=10' -fsanitize=thread -lpthread
In file included from main.c:5:
./rcu.h:191:24: warning: cast to smaller integer type 'unsigned int' from 'pthread_t _Nonnull' (aka 'struct _opaque_pthread_t *') [-Wpointer-to-int-cast]
    unsigned int tid = current_tid();
                       ^~~~~~~~~~~~~
./rcu.h:42:23: note: expanded from macro 'current_tid'
#define current_tid() (unsigned int) pthread_self()
                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
main.c:24:33: warning: cast to smaller integer type 'unsigned int' from 'pthread_t _Nonnull' (aka 'struct _opaque_pthread_t *') [-Wpointer-to-int-cast]
    printf("[reader #%u] %u\n", current_tid(), tmp->count);
                                ^~~~~~~~~~~~~
./rcu.h:42:23: note: expanded from macro 'current_tid'
#define current_tid() (unsigned int) pthread_self()
                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
main.c:36:21: warning: cast to smaller integer type 'unsigned int' from 'pthread_t _Nonnull' (aka 'struct _opaque_pthread_t *') [-Wpointer-to-int-cast]
    newval->count = current_tid();
                    ^~~~~~~~~~~~~
./rcu.h:42:23: note: expanded from macro 'current_tid'
#define current_tid() (unsigned int) pthread_self()
                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3 warnings generated.

Fixed at cf879f7.

[jserv]

Add high level description in new file README.md

[linD026]

I change the test program.
Now, the new testing will be like:

100 reader(s), 5 update run(s), 2 grace period(s)
[grace period #0]   21 reader(s)
[grace period #1]   79 reader(s)

[jserv]

Thank @linD026 for the great work!