fix: Record cached dyld images async by noahsmartin · Pull Request #7269 · getsentry/sentry-cocoa

noahsmartin · 2026-01-23T18:23:12Z

Resolves #4618 by moving the crash reporting tracking of dyld images to a background thread. Also fixes existing race conditions in that image tracker. Synchronization is now done with atomics so the crash handler can read from the added images.

VC swizzling is updated to iterate dyld loaded images directly, rather than getting them from the cache. VC tracking still does some work on the main thread, but less than the cache was doing previously. This makes it possible to disable all dyld work on the main thread if you turn off VC swizzling. There is no need for VC swizzling to use the image cache IMO since the purpose of the image cache is to provide a re-entrant API for crash reporting

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github-actions · 2026-01-23T18:23:30Z

Semver Impact of This PR

🟢 Patch (bug fixes)

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codecov · 2026-01-23T18:26:19Z

Codecov Report

❌ Patch coverage is 90.80460% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.289%. Comparing base (3a42337) to head (c2e30bf).
⚠️ Report is 12 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...entryCrash/Recording/SentryCrashBinaryImageCache.c	88.235%	5 Missing and 3 partials ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #7269       +/-   ##
=============================================
- Coverage   85.308%   85.289%   -0.020%     
=============================================
  Files          480       480               
  Lines        28622     28605       -17     
  Branches     12378     12398       +20     
=============================================
- Hits         24417     24397       -20     
- Misses        4157      4159        +2     
- Partials        48        49        +1

Files with missing lines	Coverage Δ
...ces/Swift/Core/Helper/SentryBinaryImageCache.swift	`95.789% <100.000%> (-0.365%)`	⬇️
.../Performance/SentryUIViewControllerSwizzling.swift	`83.870% <100.000%> (-1.750%)`	⬇️
...s/Swift/SentryCrash/SentryDebugImageProvider.swift	`100.000% <ø> (ø)`
Sources/Swift/SentryDependencyContainer.swift	`97.156% <ø> (-0.014%)`	⬇️
...entryCrash/Recording/SentryCrashBinaryImageCache.c	`89.534% <88.235%> (-6.210%)`	⬇️

... and 6 files with indirect coverage changes

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Sources/SentryCrash/Recording/SentryCrashBinaryImageCache.c

philipphofmann · 2026-01-26T11:46:44Z

@noahsmartin, I didn't check the code yet, as this is still a draft. Please be aware that they also need the loaded binary image in the UIViewControllerSwizzling, as pointed out here #4618 (comment). If the proposal respects this, then excellent.

github-actions · 2026-01-26T15:18:34Z

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1196.08 ms	1214.86 ms	18.78 ms
Size	24.14 KiB	1.11 MiB	1.08 MiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
`5a4353f`	1208.10 ms	1240.50 ms	32.40 ms
`92e1256`	1218.58 ms	1250.63 ms	32.04 ms
`a424cf3`	1231.36 ms	1259.62 ms	28.25 ms
`2d59844`	1208.98 ms	1245.25 ms	36.27 ms
`d4dd2bd`	1218.59 ms	1255.21 ms	36.61 ms
`09a80f2`	1214.78 ms	1237.85 ms	23.07 ms
`ee272e8`	1210.98 ms	1245.10 ms	34.12 ms
`feceb0d`	1214.55 ms	1237.04 ms	22.50 ms
`1d0feed`	1213.31 ms	1247.44 ms	34.14 ms
`aa58669`	1218.51 ms	1258.55 ms	40.04 ms

App size

Revision	Plain	With Sentry	Diff
`5a4353f`	24.14 KiB	1.07 MiB	1.04 MiB
`92e1256`	24.14 KiB	1.11 MiB	1.09 MiB
`a424cf3`	24.14 KiB	1.06 MiB	1.04 MiB
`2d59844`	24.14 KiB	1.09 MiB	1.06 MiB
`d4dd2bd`	24.14 KiB	1.10 MiB	1.08 MiB
`09a80f2`	24.14 KiB	1.10 MiB	1.08 MiB
`ee272e8`	24.14 KiB	1.10 MiB	1.08 MiB
`feceb0d`	24.14 KiB	1.10 MiB	1.08 MiB
`1d0feed`	24.14 KiB	1.05 MiB	1.03 MiB
`aa58669`	24.14 KiB	1.10 MiB	1.07 MiB

Previous results on branch: imageCacheAsync

Startup times

Revision	Plain	With Sentry	Diff
`7847014`	1222.58 ms	1241.55 ms	18.97 ms
`45a6e74`	1217.39 ms	1254.95 ms	37.56 ms
`272a47a`	1233.83 ms	1249.33 ms	15.50 ms
`f02c17c`	1212.57 ms	1246.06 ms	33.49 ms
`6dfcb08`	1209.61 ms	1251.52 ms	41.91 ms
`823a3af`	1206.16 ms	1222.51 ms	16.35 ms
`629dd8e`	1225.23 ms	1252.12 ms	26.89 ms
`a93524f`	1222.58 ms	1252.44 ms	29.86 ms
`9cfdab1`	1208.33 ms	1239.00 ms	30.67 ms
`eaac74f`	1220.91 ms	1251.35 ms	30.44 ms

App size

Revision	Plain	With Sentry	Diff
`7847014`	24.14 KiB	1.10 MiB	1.08 MiB
`45a6e74`	24.14 KiB	1.10 MiB	1.08 MiB
`272a47a`	24.14 KiB	1.10 MiB	1.08 MiB
`f02c17c`	24.14 KiB	1.10 MiB	1.07 MiB
`6dfcb08`	24.14 KiB	1.10 MiB	1.07 MiB
`823a3af`	24.14 KiB	1.08 MiB	1.06 MiB
`629dd8e`	24.14 KiB	1.10 MiB	1.08 MiB
`a93524f`	24.14 KiB	1.11 MiB	1.09 MiB
`9cfdab1`	24.14 KiB	1.10 MiB	1.07 MiB
`eaac74f`	24.14 KiB	1.11 MiB	1.08 MiB

Sources/SentryCrash/Recording/SentryCrashBinaryImageCache.c

…nch time sentrycrashbic_startCache now dispatches its work on a background queue so that the expensive _dyld_register_func_for_add_image callback (which calls dladdr for every loaded image) does not block the main thread during SDK initialization. Since the cache may not be populated yet when SentryUIViewControllerSwizzling.start() runs, replace its SentryBinaryImageCache lookup with direct synchronous iteration of _dyld_image_count/_dyld_get_image_name. Performance-sensitive users can disable UIViewController swizzling. Also fix a race condition in SentryCrashBinaryImageCache where stopCache resets g_next_index while a concurrent add_dyld_image could increment it afterwards. Move the reset into startCacheImpl and gate iterateOverImages/registerAddedCallback on g_started.

Sources/SentryCrash/Recording/SentryCrashBinaryImageCache.c

cursor

Cursor Bugbot has reviewed your changes and found 2 potential issues.

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cursor · 2026-02-13T19:51:04Z

Sources/SentryCrash/Recording/SentryCrashBinaryImageCache.c

+        = atomic_load_explicit(&g_addedCallback, memory_order_acquire);
+
+    // ---- Publish ----
+    atomic_store_explicit(&entry->ready, 1, memory_order_release);


Reused slots stay published across restarts

Medium Severity

After stop/start, g_next_index is reset but g_images[idx].ready is never cleared before slot reuse. add_dyld_image increments g_next_index before republishing, so readers can observe ready == 1 from a prior run and read stale or partially overwritten image data.

Additional Locations (1)

Sources/SentryCrash/Recording/SentryCrashBinaryImageCache.c#L239-L240

cursor · 2026-02-13T19:51:05Z

Sources/SentryCrash/Recording/SentryCrashBinaryImageCache.c

+                callback(&src->image);
            }
-            break;
+            return;


Remove callbacks still run after stop

Medium Severity

dyld_remove_image_cb does not check g_started. After sentrycrashbic_stopCache, remove events can still find old entries in g_images, flip ready, and invoke g_removedCallback. This allows cache-change notifications and state mutations after the cache is supposed to be stopped.

Additional Locations (1)

Sources/SentryCrash/Recording/SentryCrashBinaryImageCache.c#L269-L279

noahsmartin added the ready-to-merge Use this label to trigger all PR workflows label Jan 23, 2026

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noahsmartin force-pushed the imageCacheAsync branch 11 times, most recently from 6fa7332 to 20488ae Compare February 10, 2026 01:50

noahsmartin marked this pull request as ready for review February 10, 2026 19:27

noahsmartin requested review from philipphofmann and philprime as code owners February 10, 2026 19:27

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noahsmartin force-pushed the imageCacheAsync branch from 20488ae to 62a7ef8 Compare February 11, 2026 16:40

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noahsmartin force-pushed the imageCacheAsync branch from e0248e8 to 8425b43 Compare February 13, 2026 00:51

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Fix some corner cases

c2e30bf

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Performance metrics 🚀

Baseline results on branch: main

Startup times

App size

Previous results on branch: imageCacheAsync

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App size

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Reused slots stay published across restarts

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Remove callbacks still run after stop

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