Bug 288760 – [Cocoa] Assertion failure on ResourceUsageThread::platformCollectCPUData()

• Status: NEW
• Component: New Bugs

[Basuke Suzuki]

In Source/WebCore/page/cocoa/ResourceUsageThreadCocoa.mm:163, comment and ASSERT say threads[0] must be main thread, but it seems like it's not.
```
    // Main thread is always first.
    ASSERT(threads[0].dispatchQueueName == "com.apple.main-thread"_s);
```

[Basuke Suzuki]

Vector<ThreadInfo> threads at the moment is like this. Apparently first item is not "com.apple.main-thread"_s.
Of course the first thread in the actual running thread list is main thread, so this seems like collection failure. Somewhat error may happens to prevent collecting main thread information during the for look in static Vector<ThreadInfo> threadInfos().

```
threads	WTF::Vector<WebCore::ThreadInfo>	{ size = 25, capacity = 27 }	
[0]	WebCore::ThreadInfo	
sendRight	WTF::MachSendRight	
usage	float	92.0999985
threadName	WTF::String	{ length = 0, contents = '' }	
dispatchQueueName	WTF::String	{ length = 35, contents = 'com.apple.root.user-interactive-qos' }	
[1]	WebCore::ThreadInfo	
sendRight	WTF::MachSendRight	
usage	float	5.29999971
threadName	WTF::String	{ length = 0, contents = '' }	
dispatchQueueName	WTF::String	{ length = 23, contents = 'org.webkit.ImageDecoder' }	
[2]	WebCore::ThreadInfo	
sendRight	WTF::MachSendRight	
usage	float	0.100000001
threadName	WTF::String	{ length = 31, contents = 'JavaScriptCore libpas scavenger' }	
dispatchQueueName	WTF::String	{ length = 37, contents = 'com.apple.root.default-qos.overcommit' }	
[3]	WebCore::ThreadInfo	
sendRight	WTF::MachSendRight	
usage	float	0
threadName	WTF::String	{ length = 0, contents = '' }	
dispatchQueueName	WTF::String	{ length = 37, contents = 'com.apple.root.default-qos.overcommit' }	
[4]	WebCore::ThreadInfo	
sendRight	WTF::MachSendRight	
usage	float	4
threadName	WTF::String	{ length = 22, contents = 'WebCore: ResourceUsage' }	
dispatchQueueName	WTF::String	{ length = 37, contents = 'com.apple.root.default-qos.overcommit' }	
[5]	WebCore::ThreadInfo	
sendRight	WTF::MachSendRight	
usage	float	15.6000004
threadName	WTF::String	{ length = 26, contents = 'JIT Worklist Helper Thread' }	
dispatchQueueName	WTF::String	{ length = 37, contents = 'com.apple.root.default-qos.overcommit' }	
[6]	WebCore::ThreadInfo	
sendRight	WTF::MachSendRight	
usage	float	7.50000048
threadName	WTF::String	{ length = 26, contents = 'JIT Worklist Helper Thread' }	
dispatchQueueName	WTF::String	{ length = 37, contents = 'com.apple.root.default-qos.overcommit' }	
[7]	WebCore::ThreadInfo	
sendRight	WTF::MachSendRight	
usage	float	4.4000001
threadName	WTF::String	{ length = 26, contents = 'JIT Worklist Helper Thread' }	
dispatchQueueName	WTF::String	{ length = 37, contents = 'com.apple.root.default-qos.overcommit' }	
[8]	WebCore::ThreadInfo	
sendRight	WTF::MachSendRight	
usage	float	0
threadName	WTF::String	{ length = 0, contents = '' }	
dispatchQueueName	WTF::String	{ length = 37, contents = 'com.apple.root.default-qos.overcommit' }	
[9]	WebCore::ThreadInfo	
sendRight	WTF::MachSendRight	
usage	float	0
threadName	WTF::String	{ length = 18, contents = 'Heap Helper Thread' }	
dispatchQueueName	WTF::String	{ length = 37, contents = 'com.apple.root.default-qos.overcommit' }	
[10]	WebCore::ThreadInfo	
sendRight	WTF::MachSendRight	
usage	float	0
threadName	WTF::String	{ length = 18, contents = 'Heap Helper Thread' }	
dispatchQueueName	WTF::String	{ length = 37, contents = 'com.apple.root.default-qos.overcommit' }	
[11]	WebCore::ThreadInfo	
sendRight	WTF::MachSendRight	
usage	float	0
threadName	WTF::String	{ length = 18, contents = 'Heap Helper Thread' }	
dispatchQueueName	WTF::String	{ length = 37, contents = 'com.apple.root.default-qos.overcommit' }	
[12]	WebCore::ThreadInfo	
sendRight	WTF::MachSendRight	
usage	float	0
threadName	WTF::String	{ length = 0, contents = '' }	
dispatchQueueName	WTF::String	{ length = 37, contents = 'com.apple.root.default-qos.overcommit' }	
[13]	WebCore::ThreadInfo	
sendRight	WTF::MachSendRight	
usage	float	0
threadName	WTF::String	{ length = 25, contents = 'JSC Heap Collector Thread' }	
dispatchQueueName	WTF::String	{ length = 37, contents = 'com.apple.root.default-qos.overcommit' }	
...
```

[Basuke Suzuki]

I'm not sure we can move forward without getting main_thread, so I change this assertion to early return.

[Basuke Suzuki]

Pull request: https://github.com/WebKit/WebKit/pull/41564

[Basuke Suzuki]

How to reproduce:

1. Start debugging MiniBrowser in Xcode
2. Go to https://www.yahoo.com/
3. Keep scrolling for a while.

Debugger stops with the assertion failure in `WebCore: ResourceUsage` thread.

[Basuke Suzuki]

I believe Web Inspector should be opened.

[Radar WebKit Bug Importer]

<rdar://problem/146423609>