From c03ba3d91efba4861f9a16a77d60c9f311dd66b6 Mon Sep 17 00:00:00 2001
From: John Hawthorn <john@hawthorn.email>
Date: Tue, 13 May 2025 22:36:09 -0700
Subject: [PATCH] Use atomics for system_working global

Although it almost certainly works in this case, volatile is best not
used for multi-threaded code. Using atomics instead avoids warnings from
TSan.

This also simplifies some logic, as system_working was previously only
ever assigned to 1, so --system_working <= 0 should always return true
(unless it underflowed).
---
 misc/tsan_suppressions.txt |  3 ---
 thread.c                   |  2 +-
 thread_pthread.c           | 22 ++++++++++------------
 thread_win32.c             | 16 ++++++++--------
 4 files changed, 19 insertions(+), 24 deletions(-)

diff --git a/misc/tsan_suppressions.txt b/misc/tsan_suppressions.txt
index 908de1c3d93488..c788e927ddb2ec 100644
--- a/misc/tsan_suppressions.txt
+++ b/misc/tsan_suppressions.txt
@@ -30,9 +30,6 @@ race_top:RUBY_VM_INTERRUPTED_ANY
 race_top:unblock_function_set
 race_top:threadptr_get_interrupts
 
-# system_working needs to be converted to atomic
-race:system_working
-
 # It's already crashing. We're doing our best
 signal:rb_vm_bugreport
 race:check_reserved_signal_
diff --git a/thread.c b/thread.c
index 6089184ea9d101..fed955e87e3e9e 100644
--- a/thread.c
+++ b/thread.c
@@ -148,7 +148,7 @@ static int hrtime_update_expire(rb_hrtime_t *, const rb_hrtime_t);
 NORETURN(static void async_bug_fd(const char *mesg, int errno_arg, int fd));
 MAYBE_UNUSED(static int consume_communication_pipe(int fd));
 
-static volatile int system_working = 1;
+static rb_atomic_t system_working = 1;
 static rb_internal_thread_specific_key_t specific_key_count;
 
 /********************************************************************************/
diff --git a/thread_pthread.c b/thread_pthread.c
index 7811d5afbf4429..4e969c41226aca 100644
--- a/thread_pthread.c
+++ b/thread_pthread.c
@@ -2574,7 +2574,7 @@ rb_thread_wakeup_timer_thread(int sig)
     timer_thread_wakeup_force();
 
     // interrupt main thread if main thread is available
-    if (system_working) {
+    if (RUBY_ATOMIC_LOAD(system_working)) {
         rb_vm_t *vm = GET_VM();
         rb_thread_t *main_th = vm->ractor.main_thread;
 
@@ -3005,12 +3005,12 @@ timer_thread_func(void *ptr)
 
     RUBY_DEBUG_LOG("started%s", "");
 
-    while (system_working) {
+    while (RUBY_ATOMIC_LOAD(system_working)) {
         timer_thread_check_signal(vm);
         timer_thread_check_timeout(vm);
         ubf_wakeup_all_threads();
 
-        RUBY_DEBUG_LOG("system_working:%d", system_working);
+        RUBY_DEBUG_LOG("system_working:%d", RUBY_ATOMIC_LOAD(system_working));
         timer_thread_polling(vm);
     }
 
@@ -3124,18 +3124,16 @@ rb_thread_create_timer_thread(void)
 static int
 native_stop_timer_thread(void)
 {
-    int stopped;
-    stopped = --system_working <= 0;
+    RUBY_ATOMIC_SET(system_working, 0);
 
-    if (stopped) {
-        RUBY_DEBUG_LOG("wakeup send %d", timer_th.comm_fds[1]);
-        timer_thread_wakeup_force();
-        RUBY_DEBUG_LOG("wakeup sent");
-        pthread_join(timer_th.pthread_id, NULL);
-    }
+    RUBY_DEBUG_LOG("wakeup send %d", timer_th.comm_fds[1]);
+    timer_thread_wakeup_force();
+    RUBY_DEBUG_LOG("wakeup sent");
+    pthread_join(timer_th.pthread_id, NULL);
 
     if (TT_DEBUG) fprintf(stderr, "stop timer thread\n");
-    return stopped;
+
+    return 1;
 }
 
 static void
diff --git a/thread_win32.c b/thread_win32.c
index f9c268b117eec7..c656d79a1a5a17 100644
--- a/thread_win32.c
+++ b/thread_win32.c
@@ -798,14 +798,14 @@ rb_thread_create_timer_thread(void)
 static int
 native_stop_timer_thread(void)
 {
-    int stopped = --system_working <= 0;
-    if (stopped) {
-        SetEvent(timer_thread.lock);
-        native_thread_join(timer_thread.id);
-        CloseHandle(timer_thread.lock);
-        timer_thread.lock = 0;
-    }
-    return stopped;
+    RUBY_ATOMIC_SET(system_working, 0);
+
+    SetEvent(timer_thread.lock);
+    native_thread_join(timer_thread.id);
+    CloseHandle(timer_thread.lock);
+    timer_thread.lock = 0;
+
+    return 1;
 }
 
 static void