According to C# specification <https://msdn.microsoft.com/en-us/library/ms228593.aspx> :
• A read of a volatile field is called a volatile read. A volatile read has “acquire semantics”; that is, it is guaranteed to occur prior to any references to memory that occur after it in the instruction sequence. • A write of a volatile field is called a volatile write. A volatile write has “release semantics”; that is, it is guaranteed to happen after any memory references prior to the write instruction in the instruction sequence. The spec presents an example <https://msdn.microsoft.com/en-us/library/aa645755(v=vs.71).aspx> where one thread writes "data" on a non volatile variable and "publishes" the result by writing on a volatile variable that acts as a flag. The other thread checks the volatile flag and if set, it accesses the non-volatile variable that is now *guaranteed* to contain the data. It seems that Mono 4.4 (the one used in Xamarin) does not enforce these semantics or in other words does not prevent memory re-ordering in Android and iOS that have relaxed memory models due to their CPU. I have created an a test that reproduces the problem in iOS and Android Program.cs <http://mono.1490590.n4.nabble.com/file/n4668111/Program.cs> . If the access to the volatile field is replaced by Volatile.Read() and Volatile.Write(), then no-problems occur. It seems that Volatile.Read() and Volatile.Write() implement half fences in Mono, but the volatile keyword does not. Is this a bug? -- View this message in context: http://mono.1490590.n4.nabble.com/Volatile-fields-don-t-enforce-acquire-release-semantics-like-Volatile-Read-and-Volatile-Write-tp4668111.html Sent from the Mono - Dev mailing list archive at Nabble.com. _______________________________________________ Mono-devel-list mailing list Mono-devel-list@lists.ximian.com http://lists.ximian.com/mailman/listinfo/mono-devel-list
