ThreadSanitizer reports a data race

[rom1v]

Environment

• OS: Debian
• scrcpy version: 2.5
• installation method: manual build
• device model: any
• Android version: any

Describe the bug

On current master branch (v2.5), on Linux, run:

meson setup tsan -Db_sanitize=thread
ninja -Ctsan
./run tsan --no-audio

TSAN reports the following data race:

==================
WARNING: ThreadSanitizer: data race (pid=3929379)
  Read of size 5 at 0x7b0800006c00 by thread T8:
    #0 strcmp <null> (scrcpy+0x5ee18) (BuildId: f25f1d9d4465c158a50a2cbaa67900ae7da71ddc)
    #1 <null> <null> (libSDL2-2.0.so.0+0x35e83) (BuildId: 0fb7bbebd06b14aed999b59790f45986efc8fe9e)
    #2 sc_process_observer_init /home/rom/projects/scrcpy/t/../app/src/util/process.c:67:10 (scrcpy+0x112fdb) (BuildId: f25f1d9d4465c158a50a2cbaa67900ae7da71ddc)
    #3 run_server /home/rom/projects/scrcpy/t/../app/src/server.c:987:10 (scrcpy+0x10a594) (BuildId: f25f1d9d4465c158a50a2cbaa67900ae7da71ddc)
    #4 <null> <null> (libSDL2-2.0.so.0+0xa70d8) (BuildId: 0fb7bbebd06b14aed999b59790f45986efc8fe9e)

  Previous write of size 8 at 0x7b0800006c00 by main thread:
    #0 memcpy <null> (scrcpy+0x60fd4) (BuildId: f25f1d9d4465c158a50a2cbaa67900ae7da71ddc)
    #1 <null> <null> (libSDL2-2.0.so.0+0xa6421) (BuildId: 0fb7bbebd06b14aed999b59790f45986efc8fe9e)
    #2 main_scrcpy /home/rom/projects/scrcpy/t/../app/src/main.c:88:52 (scrcpy+0xdc79c) (BuildId: f25f1d9d4465c158a50a2cbaa67900ae7da71ddc)
    #3 main /home/rom/projects/scrcpy/t/../app/src/main.c:107:12 (scrcpy+0xdc628) (BuildId: f25f1d9d4465c158a50a2cbaa67900ae7da71ddc)

  Location is heap block of size 27 at 0x7b0800006c00 allocated by main thread:
    #0 malloc <null> (scrcpy+0x53010) (BuildId: f25f1d9d4465c158a50a2cbaa67900ae7da71ddc)
    #1 <null> <null> (libSDL2-2.0.so.0+0xa5896) (BuildId: 0fb7bbebd06b14aed999b59790f45986efc8fe9e)
    #2 main_scrcpy /home/rom/projects/scrcpy/t/../app/src/main.c:88:52 (scrcpy+0xdc79c) (BuildId: f25f1d9d4465c158a50a2cbaa67900ae7da71ddc)
    #3 main /home/rom/projects/scrcpy/t/../app/src/main.c:107:12 (scrcpy+0xdc628) (BuildId: f25f1d9d4465c158a50a2cbaa67900ae7da71ddc)

  Thread T8 'scrcpy-server' (tid=3929388, running) created by main thread at:
    #0 pthread_create <null> (scrcpy+0x54d8f) (BuildId: f25f1d9d4465c158a50a2cbaa67900ae7da71ddc)
    #1 <null> <null> (libSDL2-2.0.so.0+0x15147e) (BuildId: 0fb7bbebd06b14aed999b59790f45986efc8fe9e)
    #2 sc_server_start /home/rom/projects/scrcpy/t/../app/src/server.c:1067:9 (scrcpy+0x109bee) (BuildId: f25f1d9d4465c158a50a2cbaa67900ae7da71ddc)
    #3 scrcpy /home/rom/projects/scrcpy/t/../app/src/scrcpy.c:430:10 (scrcpy+0x101f2e) (BuildId: f25f1d9d4465c158a50a2cbaa67900ae7da71ddc)
    #4 main_scrcpy /home/rom/projects/scrcpy/t/../app/src/main.c:88:52 (scrcpy+0xdc79c) (BuildId: f25f1d9d4465c158a50a2cbaa67900ae7da71ddc)
    #5 main /home/rom/projects/scrcpy/t/../app/src/main.c:107:12 (scrcpy+0xdc628) (BuildId: f25f1d9d4465c158a50a2cbaa67900ae7da71ddc)

SUMMARY: ThreadSanitizer: data race (/home/rom/projects/scrcpy/t/app/scrcpy+0x5ee18) (BuildId: f25f1d9d4465c158a50a2cbaa67900ae7da71ddc) in strcmp
==================

I investigated, but I cannot understand why. I don't know if it comes from SDL or from scrcpy.

If this call does not create a new SDL thread, then the data race disappears:

scrcpy/app/src/server.c

Line 987 in a8871bf

ok = sc_process_observer_init(&observer, pid, &listener, server);

But if it creates a thread and the thread function does nothing, a data race is still reported.

If someone finds the cause, I'm interested 😉