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Merged
merged 2 commits into from
May 15, 2025
Merged

Use atomics for system_working global #13333

merged 2 commits into from
May 15, 2025

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jhawthorn
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Although it almost certainly works in this case, volatile should not be used for multi-thread synchronization. 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).

Fixes:

❯ TSAN_OPTIONS="halt_on_error=1:strip_path_prefix=$(pwd)/" ./miniruby -e 'Thread.new{}.join'
==================
WARNING: ThreadSanitizer: data race (pid=3458317)
  Write of size 4 at 0x555555e03118 by main thread:
    #0 native_stop_timer_thread thread_pthread.c:3128:15 (miniruby+0x478100) (BuildId: 15fb730468deee86fe6bbe9ca8c7e33a06fca03b)
    #1 rb_thread_stop_timer_thread thread.c:4701:37 (miniruby+0x478100)
    #2 rb_ec_cleanup eval.c:262:5 (miniruby+0x26cccc) (BuildId: 15fb730468deee86fe6bbe9ca8c7e33a06fca03b)
    #3 ruby_run_node eval.c:319:12 (miniruby+0x26d074) (BuildId: 15fb730468deee86fe6bbe9ca8c7e33a06fca03b)
    #4 rb_main main.c:42:12 (miniruby+0x14bc7c) (BuildId: 15fb730468deee86fe6bbe9ca8c7e33a06fca03b)
    #5 main main.c:62:12 (miniruby+0x14bc7c)

  Previous read of size 4 at 0x555555e03118 by thread T1:
    #0 timer_thread_func thread_pthread.c:3008:12 (miniruby+0x483e94) (BuildId: 15fb730468deee86fe6bbe9ca8c7e33a06fca03b)

  Location is global 'system_working' of size 4 at 0x555555e03118 (miniruby+0x8af118)

  Thread T1 (tid=3458319, running) created by main thread at:
    #0 pthread_create <null> (miniruby+0xc1fd9) (BuildId: 15fb730468deee86fe6bbe9ca8c7e33a06fca03b)
    #1 rb_thread_create_timer_thread thread_pthread.c:3121:5 (miniruby+0x478475) (BuildId: 15fb730468deee86fe6bbe9ca8c7e33a06fca03b)
    #2 Init_Thread thread.c:5589:5 (miniruby+0x47a908) (BuildId: 15fb730468deee86fe6bbe9ca8c7e33a06fca03b)
    #3 rb_call_inits inits.c:64:5 (miniruby+0x2b9cdc) (BuildId: 15fb730468deee86fe6bbe9ca8c7e33a06fca03b)
    #4 ruby_setup eval.c:86:9 (miniruby+0x26b8d8) (BuildId: 15fb730468deee86fe6bbe9ca8c7e33a06fca03b)
    #5 ruby_init eval.c:98:17 (miniruby+0x26ba75) (BuildId: 15fb730468deee86fe6bbe9ca8c7e33a06fca03b)
    #6 rb_main main.c:41:5 (miniruby+0x14bc6a) (BuildId: 15fb730468deee86fe6bbe9ca8c7e33a06fca03b)
    #7 main main.c:62:12 (miniruby+0x14bc6a)

SUMMARY: ThreadSanitizer: data race thread_pthread.c:3128:15 in native_stop_timer_thread
==================

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launchable-app bot commented May 14, 2025 •
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@jhawthorn
Use atomics for system_working global
c03ba3d 
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).
@jhawthorn jhawthorn force-pushed the system_working_atomic branch from 20549e4 to c03ba3d Compare May 14, 2025 22:07
@jhawthorn jhawthorn merged commit d67d169 into ruby:master May 15, 2025
82 checks passed
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