Partial Deadlock Detection

[dozn]

Brought up during togglebit's stream today, realized Odin doesn't have partial (there's other ways to bypass it) deadlock detection:

Odin

Zig (implementation)

Output

thread 1 panic: Deadlock detected
/opt/compiler-explorer/zig-master/lib/std/Thread/Mutex.zig:72:13: 0x1038c53 in lock (output.s)
            @panic("Deadlock detected");
            ^
/app/example.zig:7:15: 0x1038b7d in main (output.s)
    mutex.lock();
              ^
/opt/compiler-explorer/zig-master/lib/std/start.zig:656:37: 0x1038b22 in posixCallMainAndExit (output.s)
            const result = root.main() catch |err| {
                                    ^
/opt/compiler-explorer/zig-master/lib/std/start.zig:271:5: 0x10386fd in _start (output.s)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
Program terminated with signal: SIGSEGV

Exit code: 139

Go (implementation (unnecessarily complex for Odin due to goroutines))

Output

fatal error: all goroutines are asleep - deadlock!

goroutine 1 [sync.Mutex.Lock]:
sync.runtime_SemacquireMutex(0x3004f1340?, 0x0?, 0xc000048740?)
	/usr/local/go-faketime/src/runtime/sema.go:95 +0x25
sync.(*Mutex).lockSlow(0xc000012028)
	/usr/local/go-faketime/src/sync/mutex.go:173 +0x15d
sync.(*Mutex).Lock(...)
	/usr/local/go-faketime/src/sync/mutex.go:92
main.main()
	/tmp/sandbox3471970700/prog.go:8 +0x5d

[Feoramund]

This looks simple to implement and possibly useful during development, but it seems like something that should only be in a -debug form of the underlying structs, otherwise you introduce an extra word per lock that would be wasted space in a deadlock-free program.