threads: during abrupt thread-exit, cleanup anyways (#48223)

Closes #47590 (pthread_cancel still forbidden though, since async mode
will corrupt or deadlock the process, and synchronously tested with
cancelation disabled whenever this is a lock is just a slow
implementation of a boolean)

Refs #47201 (only deals with thread exit, not other case where this is
an issue, like cfunction exit and gc-safe-leave)

May help #46537, by blocking jl_wake_libuv before uv_library_shutdown,
and other tweaks to GC mode. For example, avoiding:

[4011824] signal (6.-6): Aborted
gsignal at /lib/x86_64-linux-gnu/libc.so.6 (unknown line)
abort at /lib/x86_64-linux-gnu/libc.so.6 (unknown line)
uv__async_send at /workspace/srcdir/libuv/src/unix/async.c:198
uv_async_send at /workspace/srcdir/libuv/src/unix/async.c:73
jl_wake_libuv at /data/vtjnash/julia1/src/jl_uv.c:44 [inlined]
JL_UV_LOCK at /data/vtjnash/julia1/src/jl_uv.c:64 [inlined]
ijl_iolock_begin at /data/vtjnash/julia1/src/jl_uv.c:72
iolock_begin at ./libuv.jl:48 [inlined]
_trywait at ./asyncevent.jl:140
wait at ./asyncevent.jl:155 [inlined]
profile_printing_listener at /data/vtjnash/julia1/usr/share/julia/stdlib/v1.10/Profile/src/Profile.jl:39
jfptr_YY.3_58617 at /data/vtjnash/julia1/usr/lib/julia/sys.so (unknown line)
_jl_invoke at /data/vtjnash/julia1/src/gf.c:2665 [inlined]
ijl_apply_generic at /data/vtjnash/julia1/src/gf.c:2866
jl_apply at /data/vtjnash/julia1/src/julia.h:1870 [inlined]
start_task at /data/vtjnash/julia1/src/task.c:1093
Aborted

Fixes #37400

Author: vtjnash

src/Makefile

@@ -286,11 +286,11 @@ $(BUILDDIR)/julia_flisp.boot: $(addprefix $(SRCDIR)/,jlfrontend.scm flisp/aliase
 
 # additional dependency links
 $(BUILDDIR)/codegen-stubs.o $(BUILDDIR)/codegen-stubs.dbg.obj: $(SRCDIR)/intrinsics.h
-$(BUILDDIR)/aotcompile.o $(BUILDDIR)/aotcompile.dbg.obj: $(SRCDIR)/jitlayers.h $(SRCDIR)/llvm-codegen-shared.h $(SRCDIR)/debug-registry.h
+$(BUILDDIR)/aotcompile.o $(BUILDDIR)/aotcompile.dbg.obj: $(SRCDIR)/jitlayers.h $(SRCDIR)/llvm-codegen-shared.h
 $(BUILDDIR)/ast.o $(BUILDDIR)/ast.dbg.obj: $(BUILDDIR)/julia_flisp.boot.inc $(SRCDIR)/flisp/*.h
 $(BUILDDIR)/builtins.o $(BUILDDIR)/builtins.dbg.obj: $(SRCDIR)/iddict.c $(SRCDIR)/builtin_proto.h
 $(BUILDDIR)/codegen.o $(BUILDDIR)/codegen.dbg.obj: $(addprefix $(SRCDIR)/,\
-	intrinsics.cpp jitlayers.h debug-registry.h intrinsics.h llvm-codegen-shared.h cgutils.cpp ccall.cpp abi_*.cpp processor.h builtin_proto.h)
+	intrinsics.cpp jitlayers.h intrinsics.h llvm-codegen-shared.h cgutils.cpp ccall.cpp abi_*.cpp processor.h builtin_proto.h)
 $(BUILDDIR)/datatype.o $(BUILDDIR)/datatype.dbg.obj: $(SRCDIR)/support/htable.h $(SRCDIR)/support/htable.inc
 $(BUILDDIR)/debuginfo.o $(BUILDDIR)/debuginfo.dbg.obj: $(addprefix $(SRCDIR)/,debuginfo.h processor.h jitlayers.h debug-registry.h)
 $(BUILDDIR)/disasm.o $(BUILDDIR)/disasm.dbg.obj: $(SRCDIR)/debuginfo.h $(SRCDIR)/processor.h
@@ -301,13 +301,13 @@ $(BUILDDIR)/gc-heap-snapshot.o $(BUILDDIR)/gc-heap-snapshot.dbg.obj: $(SRCDIR)/g
 $(BUILDDIR)/gc-alloc-profiler.o $(BUILDDIR)/gc-alloc-profiler.dbg.obj: $(SRCDIR)/gc.h $(SRCDIR)/gc-alloc-profiler.h
 $(BUILDDIR)/init.o $(BUILDDIR)/init.dbg.obj: $(SRCDIR)/builtin_proto.h
 $(BUILDDIR)/interpreter.o $(BUILDDIR)/interpreter.dbg.obj: $(SRCDIR)/builtin_proto.h
-$(BUILDDIR)/jitlayers.o $(BUILDDIR)/jitlayers.dbg.obj: $(SRCDIR)/jitlayers.h $(SRCDIR)/llvm-codegen-shared.h $(SRCDIR)/debug-registry.h
+$(BUILDDIR)/jitlayers.o $(BUILDDIR)/jitlayers.dbg.obj: $(SRCDIR)/jitlayers.h $(SRCDIR)/llvm-codegen-shared.h
 $(BUILDDIR)/jltypes.o $(BUILDDIR)/jltypes.dbg.obj: $(SRCDIR)/builtin_proto.h
 $(build_shlibdir)/libllvmcalltest.$(SHLIB_EXT): $(SRCDIR)/llvm-codegen-shared.h $(BUILDDIR)/julia_version.h
 $(BUILDDIR)/llvm-alloc-helpers.o $(BUILDDIR)/llvm-alloc-helpers.dbg.obj: $(SRCDIR)/llvm-codegen-shared.h $(SRCDIR)/llvm-pass-helpers.h $(SRCDIR)/llvm-alloc-helpers.h
 $(BUILDDIR)/llvm-alloc-opt.o $(BUILDDIR)/llvm-alloc-opt.dbg.obj: $(SRCDIR)/llvm-codegen-shared.h $(SRCDIR)/llvm-pass-helpers.h $(SRCDIR)/llvm-alloc-helpers.h
-$(BUILDDIR)/llvm-cpufeatures.o $(BUILDDIR)/llvm-cpufeatures.dbg.obj: $(SRCDIR)/jitlayers.h $(SRCDIR)/debug-registry.h
-$(BUILDDIR)/llvm-demote-float16.o $(BUILDDIR)/llvm-demote-float16.dbg.obj: $(SRCDIR)/jitlayers.h $(SRCDIR)/debug-registry.h
+$(BUILDDIR)/llvm-cpufeatures.o $(BUILDDIR)/llvm-cpufeatures.dbg.obj: $(SRCDIR)/jitlayers.h
+$(BUILDDIR)/llvm-demote-float16.o $(BUILDDIR)/llvm-demote-float16.dbg.obj: $(SRCDIR)/jitlayers.h
 $(BUILDDIR)/llvm-final-gc-lowering.o $(BUILDDIR)/llvm-final-gc-lowering.dbg.obj: $(SRCDIR)/llvm-pass-helpers.h $(SRCDIR)/llvm-codegen-shared.h
 $(BUILDDIR)/llvm-gc-invariant-verifier.o $(BUILDDIR)/llvm-gc-invariant-verifier.dbg.obj: $(SRCDIR)/llvm-codegen-shared.h
 $(BUILDDIR)/llvm-julia-licm.o $(BUILDDIR)/llvm-julia-licm.dbg.obj: $(SRCDIR)/llvm-codegen-shared.h $(SRCDIR)/llvm-alloc-helpers.h $(SRCDIR)/llvm-pass-helpers.h
@@ -323,7 +323,7 @@ $(BUILDDIR)/signal-handling.o $(BUILDDIR)/signal-handling.dbg.obj: $(addprefix $
 $(BUILDDIR)/staticdata.o $(BUILDDIR)/staticdata.dbg.obj: $(SRCDIR)/staticdata_utils.c $(SRCDIR)/precompile_utils.c $(SRCDIR)/processor.h $(SRCDIR)/builtin_proto.h
 $(BUILDDIR)/toplevel.o $(BUILDDIR)/toplevel.dbg.obj: $(SRCDIR)/builtin_proto.h
 $(BUILDDIR)/ircode.o $(BUILDDIR)/ircode.dbg.obj: $(SRCDIR)/serialize.h
-$(BUILDDIR)/pipeline.o $(BUILDDIR)/pipeline.dbg.obj: $(SRCDIR)/passes.h $(SRCDIR)/jitlayers.h $(SRCDIR)/debug-registry.h
+$(BUILDDIR)/pipeline.o $(BUILDDIR)/pipeline.dbg.obj: $(SRCDIR)/passes.h $(SRCDIR)/jitlayers.h
 
 $(addprefix $(BUILDDIR)/,threading.o threading.dbg.obj gc.o gc.dbg.obj init.c init.dbg.obj task.o task.dbg.obj): $(addprefix $(SRCDIR)/,threading.h)
 $(addprefix $(BUILDDIR)/,APInt-C.o APInt-C.dbg.obj runtime_intrinsics.o runtime_intrinsics.dbg.obj): $(SRCDIR)/APInt-C.h
@@ -437,8 +437,14 @@ $(build_shlibdir)/lib%Plugin.$(SHLIB_EXT): $(SRCDIR)/clangsa/%.cpp $(LLVM_CONFIG
 # before attempting this static analysis, so that all necessary headers
 # and dependencies are properly installed:
 #   make -C src install-analysis-deps
+ANALYSIS_DEPS := llvm clang llvm-tools libuv utf8proc
+ifeq ($(OS),Darwin)
+ANALYSIS_DEPS += llvmunwind
+else ifneq ($(OS),WINNT)
+ANALYSIS_DEPS += unwind
+endif
 install-analysis-deps:
-	$(MAKE) -C $(JULIAHOME)/deps install-llvm install-clang install-llvm-tools install-libuv install-utf8proc install-unwind
+	$(MAKE) -C $(JULIAHOME)/deps $(addprefix install-,$(ANALYSIS_DEPS))
 
 analyzegc-deps-check: $(BUILDDIR)/julia_version.h $(BUILDDIR)/julia_flisp.boot.inc $(BUILDDIR)/jl_internal_funcs.inc
 ifeq ($(USE_BINARYBUILDER_LLVM),0)

src/codegen-stubs.c

@@ -58,7 +58,7 @@ JL_DLLEXPORT int jl_compile_extern_c_fallback(LLVMOrcThreadSafeModuleRef llvmmod
     return 0;
 }
 
-JL_DLLEXPORT void jl_teardown_codegen_fallback(void)
+JL_DLLEXPORT void jl_teardown_codegen_fallback(void) JL_NOTSAFEPOINT
 {
 }
 

src/codegen.cpp

@@ -8874,7 +8874,7 @@ extern "C" JL_DLLEXPORT void jl_init_codegen_impl(void)
     init_jit_functions();
 }
 
-extern "C" JL_DLLEXPORT void jl_teardown_codegen_impl()
+extern "C" JL_DLLEXPORT void jl_teardown_codegen_impl() JL_NOTSAFEPOINT
 {
     // output LLVM timings and statistics
     reportAndResetTimings();

src/debug-registry.h

@@ -3,8 +3,6 @@
 #include <llvm/IR/DataLayout.h>
 
 #include "julia.h"
-#include "julia_internal.h"
-#include "processor.h"
 
 #include <map>
 #include <mutex>

src/debuginfo.cpp

@@ -39,10 +39,12 @@ using namespace llvm;
 #include <set>
 #include <mutex>
 #include "julia_assert.h"
+#include "debug-registry.h"
 
+static JITDebugInfoRegistry DebugRegistry;
 
 static JITDebugInfoRegistry &getJITDebugRegistry() JL_NOTSAFEPOINT {
-    return jl_ExecutionEngine->getDebugInfoRegistry();
+    return DebugRegistry;
 }
 
 struct debug_link_info {

src/dlload.c

@@ -70,8 +70,6 @@ const char *jl_crtdll_name = CRTDLL_BASENAME ".dll";
 
 #define PATHBUF 4096
 
-#define JL_RTLD(flags, FLAG) (flags & JL_RTLD_ ## FLAG ? RTLD_ ## FLAG : 0)
-
 #ifdef _OS_WINDOWS_
 void win32_formatmessage(DWORD code, char *reason, int len) JL_NOTSAFEPOINT
 {
@@ -160,12 +158,21 @@ JL_DLLEXPORT void *jl_dlopen(const char *filename, unsigned flags) JL_NOTSAFEPOI
     if (!len) return NULL;
     WCHAR *wfilename = (WCHAR*)alloca(len * sizeof(WCHAR));
     if (!MultiByteToWideChar(CP_UTF8, 0, filename, -1, wfilename, len)) return NULL;
-    HANDLE lib = LoadLibraryExW(wfilename, NULL, LOAD_WITH_ALTERED_SEARCH_PATH);
-    if (lib)
-        needsSymRefreshModuleList = 1;
+    HANDLE lib;
+    if (flags & JL_RTLD_NOLOAD) {
+        lib = GetModuleHandleW(wfilename);
+    }
+    else {
+        lib = LoadLibraryExW(wfilename, NULL, LOAD_WITH_ALTERED_SEARCH_PATH);
+        if (lib)
+            needsSymRefreshModuleList = 1;
+    }
     return lib;
 }
 #else
+
+#define JL_RTLD(flags, FLAG) (flags & JL_RTLD_ ## FLAG ? RTLD_ ## FLAG : 0)
+
 JL_DLLEXPORT JL_NO_SANITIZE void *jl_dlopen(const char *filename, unsigned flags) JL_NOTSAFEPOINT
 {
     /* The sanitizers break RUNPATH use in dlopen for annoying reasons that are
@@ -186,7 +193,7 @@ JL_DLLEXPORT JL_NO_SANITIZE void *jl_dlopen(const char *filename, unsigned flags
         dlclose(libdl_handle);
         assert(dlopen);
     }
-    // The real interceptors check the validty of the string here, but let's
+    // The real interceptors check the validity of the string here, but let's
     // just skip that for the time being.
 #endif
     void *hnd = dlopen(filename,

src/gc.c

@@ -145,7 +145,7 @@ static _Atomic(int) support_conservative_marking = 0;
  * threads that enters `jl_gc_collect()` at the same time (or later calling
  * from unmanaged code) will wait in `jl_gc_collect()` until the GC is finished.
  *
- * Before starting the mark phase the GC thread calls `jl_safepoint_gc_start()`
+ * Before starting the mark phase the GC thread calls `jl_safepoint_start_gc()`
  * and `jl_gc_wait_for_the_world()`
  * to make sure all the thread are in a safe state for the GC. The function
  * activates the safepoint and wait for all the threads to get ready for the

src/gf.c

@@ -2320,21 +2320,23 @@ jl_value_t *jl_fptr_const_return(jl_value_t *f, jl_value_t **args, uint32_t narg
 
 jl_value_t *jl_fptr_args(jl_value_t *f, jl_value_t **args, uint32_t nargs, jl_code_instance_t *m)
 {
+    jl_fptr_args_t invoke = jl_atomic_load_relaxed(&m->specptr.fptr1);
     while (1) {
-        jl_fptr_args_t invoke = jl_atomic_load_relaxed(&m->specptr.fptr1);
         if (invoke)
             return invoke(f, args, nargs);
+        invoke = jl_atomic_load_acquire(&m->specptr.fptr1); // require forward progress with acquire annotation
     }
 }
 
 jl_value_t *jl_fptr_sparam(jl_value_t *f, jl_value_t **args, uint32_t nargs, jl_code_instance_t *m)
 {
     jl_svec_t *sparams = m->def->sparam_vals;
     assert(sparams != jl_emptysvec);
+    jl_fptr_sparam_t invoke = jl_atomic_load_relaxed(&m->specptr.fptr3);
     while (1) {
-        jl_fptr_sparam_t invoke = jl_atomic_load_relaxed(&m->specptr.fptr3);
         if (invoke)
             return invoke(f, args, nargs, sparams);
+        invoke = jl_atomic_load_acquire(&m->specptr.fptr3); // require forward progress with acquire annotation
     }
 }
 

src/init.c

@@ -199,7 +199,7 @@ static void jl_close_item_atexit(uv_handle_t *handle)
 
 // This prevents `ct` from returning via error handlers or other unintentional
 // means by destroying some old state before we start destroying that state in atexit hooks.
-void jl_task_frame_noreturn(jl_task_t *ct);
+void jl_task_frame_noreturn(jl_task_t *ct) JL_NOTSAFEPOINT;
 
 // cause this process to exit with WEXITSTATUS(signo), after waiting to finish all julia, C, and C++ cleanup
 JL_DLLEXPORT void jl_exit(int exitcode)
@@ -246,26 +246,26 @@ JL_DLLEXPORT void jl_atexit_hook(int exitcode) JL_NOTSAFEPOINT_ENTER
 
     jl_task_t *ct = jl_get_current_task();
 
-    // we are about to start tearing everything down, so lets try not to get
-    // upset by the local mess of things when we run the user's _atexit hooks
-    if (ct)
+    if (ct) {
+        if (exitcode == 0)
+            jl_write_compiler_output();
+        // we are about to start tearing everything down, so lets try not to get
+        // upset by the local mess of things when we run the user's _atexit hooks
+        // this also forces us into a GC-unsafe region without a safepoint
         jl_task_frame_noreturn(ct);
+    }
 
     if (ct == NULL && jl_base_module)
         ct = container_of(jl_adopt_thread(), jl_task_t, gcstack);
+    else if (ct != NULL)
+        jl_gc_safepoint_(ct->ptls);
 
-    if (exitcode == 0)
-        jl_write_compiler_output();
     jl_print_gc_stats(JL_STDERR);
     if (jl_options.code_coverage)
         jl_write_coverage_data(jl_options.output_code_coverage);
     if (jl_options.malloc_log)
         jl_write_malloc_log();
 
-    int8_t old_state;
-    if (ct)
-        old_state = jl_gc_unsafe_enter(ct->ptls);
-
     if (jl_base_module) {
         jl_value_t *f = jl_get_global(jl_base_module, jl_symbol("_atexit"));
         if (f != NULL) {
@@ -334,19 +334,25 @@ JL_DLLEXPORT void jl_atexit_hook(int exitcode) JL_NOTSAFEPOINT_ENTER
         // force libuv to spin until everything has finished closing
         loop->stop_flag = 0;
         while (uv_run(loop, UV_RUN_DEFAULT)) { }
-        JL_UV_UNLOCK();
+        jl_wake_libuv(); // set the async pending flag, so that future calls are immediate no-ops on other threads
+                         // we would like to guarantee this, but cannot currently, so there is still a small race window
+                         // that needs to be fixed in libuv
+    }
+    if (ct)
+        (void)jl_gc_safe_enter(ct->ptls); // park in gc-safe
+    if (loop != NULL) {
+        // TODO: consider uv_loop_close(loop) here, before shutdown?
+        uv_library_shutdown();
+        // no JL_UV_UNLOCK(), since it is now torn down
     }
 
-    // TODO: Destroy threads
+    // TODO: Destroy threads?
 
-    jl_destroy_timing();
+    jl_destroy_timing(); // cleans up the current timing_stack for noreturn
 #ifdef ENABLE_TIMINGS
     jl_print_timings();
 #endif
-
-    jl_teardown_codegen();
-    if (ct)
-        jl_gc_unsafe_leave(ct->ptls, old_state);
+    jl_teardown_codegen(); // prints stats
 }
 
 JL_DLLEXPORT void jl_postoutput_hook(void)
@@ -713,13 +719,32 @@ JL_DLLEXPORT int jl_default_debug_info_kind;
 
 JL_DLLEXPORT void julia_init(JL_IMAGE_SEARCH rel)
 {
-    jl_default_debug_info_kind = 0;
-
+    // initialize many things, in no particular order
+    // but generally running from simple platform things to optional
+    // configuration features
     jl_init_timing();
     // Make sure we finalize the tls callback before starting any threads.
     (void)jl_get_pgcstack();
-    jl_safepoint_init();
+
+    // initialize backtraces
+    jl_init_profile_lock();
+#ifdef _OS_WINDOWS_
+    uv_mutex_init(&jl_in_stackwalk);
+    SymSetOptions(SYMOPT_UNDNAME | SYMOPT_DEFERRED_LOADS | SYMOPT_LOAD_LINES | SYMOPT_IGNORE_CVREC);
+    if (!SymInitialize(GetCurrentProcess(), "", 1)) {
+        jl_safe_printf("WARNING: failed to initialize stack walk info\n");
+    }
+    needsSymRefreshModuleList = 0;
+#else
+    // nongnu libunwind initialization is only threadsafe on architecture where the
+    // author could access TSAN, per https://github.com/libunwind/libunwind/pull/109
+    // so we need to do this once early (before threads)
+    rec_backtrace(NULL, 0, 0);
+#endif
+
     libsupport_init();
+    jl_safepoint_init();
+    jl_page_size = jl_getpagesize();
     htable_new(&jl_current_modules, 0);
     JL_MUTEX_INIT(&jl_modules_mutex);
     jl_precompile_toplevel_module = NULL;
@@ -732,7 +757,6 @@ JL_DLLEXPORT void julia_init(JL_IMAGE_SEARCH rel)
     restore_signals();
     jl_init_intrinsic_properties();
 
-    jl_page_size = jl_getpagesize();
     jl_prep_sanitizers();
     void *stack_lo, *stack_hi;
     jl_init_stack_limits(1, &stack_lo, &stack_hi);
@@ -746,17 +770,12 @@ JL_DLLEXPORT void julia_init(JL_IMAGE_SEARCH rel)
                             (HMODULE*)&jl_libjulia_handle)) {
         jl_error("could not load base module");
     }
-    jl_ntdll_handle = jl_dlopen("ntdll.dll", 0); // bypass julia's pathchecking for system dlls
-    jl_kernel32_handle = jl_dlopen("kernel32.dll", 0);
-    jl_crtdll_handle = jl_dlopen(jl_crtdll_name, 0);
-    jl_winsock_handle = jl_dlopen("ws2_32.dll", 0);
-    uv_mutex_init(&jl_in_stackwalk);
-    SymSetOptions(SYMOPT_UNDNAME | SYMOPT_DEFERRED_LOADS | SYMOPT_LOAD_LINES | SYMOPT_IGNORE_CVREC);
-    if (!SymInitialize(GetCurrentProcess(), "", 1)) {
-        jl_printf(JL_STDERR, "WARNING: failed to initialize stack walk info\n");
-    }
+    jl_ntdll_handle = jl_dlopen("ntdll.dll", JL_RTLD_NOLOAD); // bypass julia's pathchecking for system dlls
+    jl_kernel32_handle = jl_dlopen("kernel32.dll", JL_RTLD_NOLOAD);
+    jl_crtdll_handle = jl_dlopen(jl_crtdll_name, JL_RTLD_NOLOAD);
+    jl_winsock_handle = jl_dlopen("ws2_32.dll", JL_RTLD_NOLOAD);
+    HMODULE jl_dbghelp = (HMODULE) jl_dlopen("dbghelp.dll", JL_RTLD_NOLOAD);
     needsSymRefreshModuleList = 0;
-    HMODULE jl_dbghelp = (HMODULE) jl_dlopen("dbghelp.dll", 0);
     if (jl_dbghelp)
         jl_dlsym(jl_dbghelp, "SymRefreshModuleList", (void **)&hSymRefreshModuleList, 1);
 #else
@@ -774,7 +793,6 @@ JL_DLLEXPORT void julia_init(JL_IMAGE_SEARCH rel)
     }
 
     jl_init_rand();
-    jl_init_profile_lock();
     jl_init_runtime_ccall();
     jl_init_tasks();
     jl_init_threading();

src/jitlayers.h

@@ -19,7 +19,8 @@
 
 #include <llvm/Target/TargetMachine.h>
 #include "julia_assert.h"
-#include "debug-registry.h"
+#include "julia.h"
+#include "julia_internal.h"
 #include "platform.h"
 
 #include <stack>
@@ -487,10 +488,6 @@ class JuliaOJIT {
 
     size_t getTotalBytes() const JL_NOTSAFEPOINT;
 
-    JITDebugInfoRegistry &getDebugInfoRegistry() JL_NOTSAFEPOINT {
-        return DebugRegistry;
-    }
-
     jl_locked_stream &get_dump_emitted_mi_name_stream() JL_NOTSAFEPOINT {
         return dump_emitted_mi_name_stream;
     }
@@ -512,8 +509,6 @@ class JuliaOJIT {
     orc::JITDylib &GlobalJD;
     orc::JITDylib &JD;
 
-    JITDebugInfoRegistry DebugRegistry;
-
     //Map and inc are guarded by RLST_mutex
     std::mutex RLST_mutex{};
     int RLST_inc = 0;