Implement redisAtomic to replace _Atomic C11 builtin (#7707)

Redis 6.0 introduces I/O threads, it is so cool and efficient, we use C11
_Atomic to establish inter-thread synchronization without mutex. But the
compiler that must supports C11 _Atomic can compile redis code, that brings a
lot of inconvenience since some common platforms can't support by default such
as CentOS7, so we want to implement redis atomic type to make it more portable.

We have implemented our atomic variable for redis that only has 'relaxed'
operations in src/atomicvar.h, so we implement some operations with
'sequentially-consistent', just like the default behavior of C11 _Atomic that
can establish inter-thread synchronization. And we replace all uses of C11
_Atomic with redis atomic variable.

Our implementation of redis atomic variable uses C11 _Atomic, __atomic or
__sync macros if available, it supports most common platforms, and we will
detect automatically which feature we use. In Makefile we use a dummy file to
detect if the compiler supports C11 _Atomic. Now for gcc, we can compile redis
code theoretically if your gcc version is not less than 4.1.2(starts to support
__sync_xxx operations). Otherwise, we remove use mutex fallback to implement
redis atomic variable for performance and test. You will get compiling errors
if your compiler doesn't support all features of above.

For cover redis atomic variable tests, we add other CI jobs that build redis on
CentOS6 and CentOS7 and workflow daily jobs that run the tests on them.
For them, we just install gcc by default in order to cover different compiler
versions, gcc is 4.4.7 by default installation on CentOS6 and 4.8.5 on CentOS7.

We restore the feature that we can test redis with Helgrind to find data race
errors. But you need install Valgrind in the default path configuration firstly
before running your tests, since we use macros in helgrind.h to tell Helgrind
inter-thread happens-before relationship explicitly for avoiding false positives.
Please open an issue on github if you find data race errors relate to this commit.

Unrelated:
- Fix redefinition of typedef 'RedisModuleUserChangedFunc'
  For some old version compilers, they will report errors or warnings, if we
  re-define function type.

1 files changed, 12 insertions, 2 deletions

diff --git a/src/Makefile b/src/Makefile
index 9ff344c6a..6414b8c78 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -20,7 +20,7 @@ DEPENDENCY_TARGETS=hiredis linenoise lua hdr_histogram
 NODEPS:=clean distclean
 
 # Default settings
-STD=-std=c11 -pedantic -DREDIS_STATIC=''
+STD=-pedantic -DREDIS_STATIC=''
 ifneq (,$(findstring clang,$(CC)))
 ifneq (,$(findstring FreeBSD,$(uname_S)))
   STD+=-Wno-c11-extensions
@@ -29,6 +29,16 @@ endif
 WARN=-Wall -W -Wno-missing-field-initializers
 OPT=$(OPTIMIZATION)
 
+# Detect if the compiler supports C11 _Atomic
+C11_ATOMIC := $(shell sh -c 'echo "\#include <stdatomic.h>" > foo.c; \
+	$(CC) -std=c11 -c foo.c -o foo.o &> /dev/null; \
+	if [ -f foo.o ]; then echo "yes"; rm foo.o; fi; rm foo.c')
+ifeq ($(C11_ATOMIC),yes)
+	STD+=-std=c11
+else
+	STD+=-std=c99
+endif
+
 PREFIX?=/usr/local
 INSTALL_BIN=$(PREFIX)/bin
 INSTALL=install
@@ -367,7 +377,7 @@ valgrind:
 	$(MAKE) OPTIMIZATION="-O0" MALLOC="libc"
 
 helgrind:
-	$(MAKE) OPTIMIZATION="-O0" MALLOC="libc" CFLAGS="-D__ATOMIC_VAR_FORCE_SYNC_MACROS"
+	$(MAKE) OPTIMIZATION="-O0" MALLOC="libc" CFLAGS="-D__ATOMIC_VAR_FORCE_SYNC_MACROS" REDIS_CFLAGS="-I/usr/local/include" REDIS_LDFLAGS="-L/usr/local/lib"
 
 src/help.h:
 	@../utils/generate-command-help.rb > help.h