Fix for OpenMP thread affinity crashes on Android devices

[looechao]

Issue

FluidSynth crashes on multiple Android devices (predominantly Xiaomi models) when loading SoundFonts.
These crashes occur when OpenMP attempts to set thread affinity during parallel sample loading in
fluid_defsfont_load_all_sampledata().

Crash stack trace shows failure in KMPNativeAffinity::Mask::set_system_affinity() with EINVAL error.

Root Cause

This is a documented issue in Android NDK's OpenMP implementation. When thread affinity setting fails on certain devices, libomp.so terminates the process instead of handling the error gracefully. The issue (Android NDK #1180) remains unresolved as it's difficult to reproduce. It still affects Xiaomi/Redmi devices.

11 libomp.so __kmp_abort_process + 52
12 libomp.so __kmp_fatal + 128
13 libomp.so KMPNativeAffinity::Mask::set_system_affinity(bool) const + 208
14 libomp.so __kmp_affinity_set_init_mask + 864
15 libomp.so __kmp_parallel_initialize + 320
16 libomp.so __kmp_fork_call + 160
17 libomp.so __kmpc_fork_call + 236
18 libfluidsynth.so fluid_defsfont.c - line 398  fluid_defsfont_load_all_sampledata + 398
19 libfluidsynth.so fluid_defsfont.c - line 540  fluid_defsfont_load + 540
20 libfluidsynth.so fluid_defsfont.c - line 108  fluid_defsfloader_load + 108
21 libfluidsynth.so fluid_synth.c - line 5365  fluid_synth_sfload + 5365

Solution

Disable KMP_AFFINITY on Android by setting the environment variable early in initialization. This approach is successfully used in other libraries (e.g., Tencent's ncnn).

Affected Devices

• Xiaomi Redmi Note 13 Pro | Redmi Note12 Turbo | Xiaomi 12Pro | Xiaomi 12 ultra

• Confirmed on:
  • Xiaomi Redmi Note 13 Pro (Android 15)
  • Xiaomi 12 Pro

References

• Android NDK Issue (open since 2020): [BUG] OpenMP > OMP: System error #22: Invalid argument android/ndk#1180
• Recent report (2024): [BUG] OpenMP > OMP: System error #22: Invalid argument android/ndk#1180 (comment)
• Similar fix in ncnn: fix openmp affinity abort when cpu goes offline Tencent/ncnn#4370

Note: While setting KMP_AFFINITY=disabled in JNI_OnLoad successfully resolves the crashes in our application, I have not yet verified if placing this setting within FluidSynth's initialization will have the same effect. This issue is raised to bring attention to the problem and propose a potential solution that worked at the application level.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[derselbst]

Excellent finding, thanks! I moved your code to fluid_synth_init(), which will be executed before the first synth instance is created. This will ensure the workaround getting applied, no matter how people are using fluidsynth (i.e. executable vs. via API only).
Feel free to test it. Android binaries will shortly become available here: https://dev.azure.com/tommbrt/tommbrt/_build/results?buildId=12127&view=artifacts&pathAsName=false&type=publishedArtifacts