Re: Please disprove this Double-Checked Locking "fix"

Pete Becker <>
Tue, 26 Apr 2011 14:30:04 -0400
On 2011-04-26 14:16:33 -0400, Joshua Maurice said:

This is largely due to hardware "reorderings",
but let me quote the paper for the relevant bit:

Nothing you do can alter the fundamental problem: you need to be able
to specify a constraint on instruction ordering, and your language
gives you no way to do it.

To emphasize, it might be the compiler reordering it, it might be the
hardware reordering it,

Let me underscore the problem, as the quotation above misses part of
the issue. Even when the instructions are executed in exactly the order
that you want them to be executed, different threads can see results in
a different order from the order in which the thread doing the stores
actually did them.

When data is shared between threads and at least one thread is writing
that data, all accesses to that data must be synchronized.

C++0x says that the behavior of a program that does not synchronize
such accesses is undefined.

Roundhouse Consulting, Ltd. ( Author of "The
Standard C++ Library Extensions: a Tutorial and Reference

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