Support synchronization features.

[kekyo]

Basic features

• [ ] System.Threading.Interlocked
• [X] System.Threading.Monitor

Advanced features

• [ ] System.Threading.WaitHandle
• [ ] System.Threading.Mutex
• [ ] System.Threading.Event
• [ ] System.Threading.ReaderWriterLock

[kekyo]

Related #50

[kekyo]

41cf424cffe5668d98fe0258ed1c012958b7f09f

Monitor lock feature implemented 🎉

[kekyo]

It's bit difference handling.

• The constant instance (currently only System_String with generated IL2C_CONST_STRING() macro), they can't set any instance flag at the IL2C_REF_HEADER.characteristic. Because it'll place in the rdata section (exactly ROM area for devices.) So, the monitor lock management area is searched always.
• The standard instance (System_Object and others) can set characteristic flags. IL2C memorize acquire monitor lock into it (with IL2C_CHARASTERISTIC_ACQUIRED_MONITOR_LOCK.) Then, the GC will collect faster for analyzing acquired or not.

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Background: I think about we'll use monitor lock with custom allocated instances instead a string instance or same as.

// .NET can it, but we'll often don't this:
lock ("ABC")
{ ... }

lock (typeof(Hoge))
{ ... }