[llvm-dev] Purpose of Epoch Trackers

[Praveen Velliengiri via llvm-dev]

Oh, then I think it may results from accessing / mutating data from
different threads with different timed sequences of events. But I'm not
sure which part in my code triggers this behaviour.
I will do more investigation tomorrow and let you know
Thanks

On Fri, 21 Jun 2019 at 23:31, Eli Friedman <efriedma at quicinc.com> wrote:

> Epoch tracking is meant to catch cases where an iterator might point to an
> invalid address due to another operation on the same DenseMap, on the same
> thread.  For example, if you have a for loop that iterates over a DenseMap,
> and insert an element into that DenseMap inside the loop body.
>
>
>
> Neither DenseMap nor the epoch tracking is threadsafe; if it’s catching a
> race condition, you’re getting lucky.
>
>
>
> -Eli
>
>
>
> *From:* llvm-dev <llvm-dev-bounces at lists.llvm.org> *On Behalf Of *Praveen
> Velliengiri via llvm-dev
> *Sent:* Friday, June 21, 2019 6:27 AM
> *To:* llvm-dev <llvm-dev at lists.llvm.org>
> *Subject:* [EXT] [llvm-dev] Purpose of Epoch Trackers
>
>
>
> Hi all,
>
> I'm dealing with the multi-threaded code, in one of executions of the
> program I hitting an assertion failure, I'm not always getting the
> assertion failure when I run the executable but it occurs for say (1 in 10)
> times. I think there may be an thread race condition. I don't know which is
> the root cause of this error because the assertion not explicitly occurs in
> my code, it occurs in the library code which I'm using in my threads.
>
>
>
> Assertion I'm getting is this:
>
>  Global Value is CRO:
> /home/preejackie/spicy/orcs/llvm/include/llvm/ADT/DenseMap.h:1242: bool
> llvm::DenseMapIterator<const llvm::Value *,
> llvm::StringMapEntry<llvm::Value *> *, llvm::DenseMapInfo<const llvm::Value
> *>, llvm::detail::DenseMapPair<const llvm::Value *,
> llvm::StringMapEntry<llvm::Value *> *>, false>::operator!=(const
> llvm::DenseMapIterator::ConstIterator &) const [KeyT = const llvm::Value *,
> ValueT = llvm::StringMapEntry<llvm::Value *> *, KeyInfoT =
> llvm::DenseMapInfo<const llvm::Value *>, Bucket =
> llvm::detail::DenseMapPair<const llvm::Value *,
> llvm::StringMapEntry<llvm::Value *> *>, IsConst = false]: Assertion `(!Ptr
> || isHandleInSync()) && "handle not in sync!"' failed.
>
>
>
> It seems like the given assertion is defined in Epochtracker.h only for
> the debug build. My question is what is the purpose of Epochtrackers,h? Is
> it there to catch the race condition when accessing the densemap
> concurrently ?
>
>
>
> Please tell me if you need more info
>
> Thanks
>
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