[phobos] std.parallelism's unit tests randomly hang on win32

[Sean Kelly]

Is core.atomic not saving and restoring a register it should?

Sent from my iPhone

On May 1, 2011, at 12:44 PM, David Simcha <dsimcha at gmail.com> wrote:

> Update:  The segfaults on Linux64 are also being caused by the low order bit corruption bug.  Whenever I look at the chain of pointer dereferences in GDB by viewing the registers and disassembly on crash, the segfault is always caused by dereferencing a pointer to some memory address that's clearly illegal.  (On x64 user mode addresses can't have their high order bits set, and the addresses being dereferenced often do.  See http://en.wikipedia.org/wiki/X64#Virtual_address_space_details .)  This wild pointer is obtained by dereferencing another pointer whose low order bits are always equal to TaskStatus.done.  For example, if TaskStatus.done == 2, the pointer might be something like 0x0000ABCD EF123402.  If TaskStatus.done == 1, it will be something like 0x0000ABCD EF123401.
> 
> Therefore, somehow the low order bits of pointers are getting corrupted with the value of TaskStatus.done in several places.  This is strong evidence that the underlying issue is a codegen bug or a bug in the ASM for the atomic ops, not a concurrency bug.
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