Fix macOS broker deadlock by processing CFRunLoop in MacMainThreadScheduler - #5966
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embetten wants to merge 4 commits into
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Fix macOS broker deadlock by processing CFRunLoop in MacMainThreadScheduler#5966embetten wants to merge 4 commits into
embetten wants to merge 4 commits into
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…eduler On macOS, the native MSAL broker runtime may use dispatch_sync to the main GCD queue (e.g. during FallbackToNativeMsal on devices without an SSO extension). The existing Thread.Sleep in the message loop prevents the main thread from servicing the GCD queue, causing a deadlock. Replace Thread.Sleep with CFRunLoopRunInMode on macOS so dispatch_sync calls targeting the main queue can execute while the scheduler waits for new work.
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Pull request overview
Note
Copilot was unable to run its full agentic suite in this review.
Fixes a macOS deadlock in MacMainThreadScheduler.StartMessageLoop() by pumping the CoreFoundation run loop (servicing GCD main-queue dispatch_sync) instead of using Thread.Sleep when running on macOS.
Changes:
- Added macOS CoreFoundation P/Invoke bindings in a nested
CoreFoundationInteropclass. - Replaced
Thread.SleepwithCFRunLoopRunInModeon macOS while preservingThread.Sleepelsewhere.
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| private static IntPtr s_defaultMode; | ||
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| private static IntPtr GetDefaultMode() | ||
| { | ||
| if (s_defaultMode == IntPtr.Zero) | ||
| { | ||
| s_defaultMode = CFStringCreateWithCString( | ||
| IntPtr.Zero, "kCFRunLoopDefaultMode", KCFStringEncodingUTF8); | ||
| } | ||
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| return s_defaultMode; |
Author
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Copilot apply changes based on the comments in this thread |
Gladwin Johnson (gladjohn)
requested review from
Ashok Kumar Ramakrishnan (ashok672) and
fengga
May 1, 2026 02:57
Contributor
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Ashok Kumar Ramakrishnan (@ashok672) fengga can you review this please |
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| [DllImport(CoreFoundationLib)] | ||
| private static extern IntPtr CFStringCreateWithCString( | ||
| IntPtr alloc, string cStr, uint encoding); | ||
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| private static readonly Lazy<IntPtr> s_defaultMode = new Lazy<IntPtr>(() => | ||
| CFStringCreateWithCString(IntPtr.Zero, "kCFRunLoopDefaultMode", KCFStringEncodingUTF8)); | ||
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| private static IntPtr GetDefaultMode() => s_defaultMode.Value; |
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| [DllImport(CoreFoundationLib)] | ||
| private static extern int CFRunLoopRunInMode( | ||
| IntPtr mode, double seconds, | ||
| [MarshalAs(UnmanagedType.I1)] bool returnAfterSourceHandled); | ||
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| [DllImport(CoreFoundationLib)] | ||
| private static extern IntPtr CFStringCreateWithCString( | ||
| IntPtr alloc, string cStr, uint encoding); |
fengga
requested changes
May 5, 2026
fengga
left a comment
fengga
left a comment
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Thanks for the PR, but I'd say Thread.Sleep() in this class is by design, and cannot replaced by RunloopRun() here - RunloopRun is called inside MSALRuntime. Let's fix the issues from other angles
Travis Walker (trwalke)
previously approved these changes
May 20, 2026
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On macOS, MacMainThreadScheduler.StartMessageLoop() uses Thread.Sleep to wait between processing queued actions. However, the native MSAL broker runtime may use dispatch_sync to the main GCD queue (e.g. during FallbackToNativeMsal on devices without an SSO extension). Because Thread.Sleep does not service the GCD queue, dispatch_sync blocks forever waiting for the main thread — resulting in a deadlock.
This PR replaces Thread.Sleep with CFRunLoopRunInMode on macOS, which processes pending GCD dispatch calls while waiting. On non-macOS platforms, the existing Thread.Sleep behavior is preserved.
Fixes #
#5940
Changes proposed in this request
Testing
Performance impact
CFRunLoopRunInMode with the same sleep interval behaves equivalently to Thread.Sleep for timing purposes, while additionally servicing the run loop. No measurable performance difference expected.
Documentation
I am not aware of any related documentation