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https://issues.apache.org/jira/browse/KUDU-2011?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16011100#comment-16011100
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Todd Lipcon commented on KUDU-2011:
-----------------------------------
That seems reasonable to me. I guess the reason for shared_ptr<faststring>
instead of just a 'move' style single-owner faststring is that, in the common
case of an RPC success, you want to reuse the underlying buffer, right?
We should make it clear in the API docs for this type of sidecar that, when the
RPC completes, the caller should only feel free to reuse the buffer after a
successful completion, right? I wonder if there is any other way we can make
this API more natural to "do the right thing".
> Request-side sidecars cannot be safely destroyed on timeout
> -----------------------------------------------------------
>
> Key: KUDU-2011
> URL: https://issues.apache.org/jira/browse/KUDU-2011
> Project: Kudu
> Issue Type: Bug
> Reporter: Henry Robinson
> Assignee: Henry Robinson
>
> If a timeout occurs while sending a request-side sidecar (see KUDU-1866), the
> RPC callback may be invoked before the outbound transfer has been completely
> written.
> This is the last notification from the RPC layer that the caller will get, so
> you might expect them to delete the sidecar payload at that point, but it's
> not safe to do so. In fact, with a slow sender there is no way for the caller
> to know when it's safe to delete the payload. There's no problem for the
> protobuf message data, as it's serialized during the blocking part of an
> async call, and that memory is tied to the lifetime of the outbound call,
> which is managed by the RPC layer.
> Ownership of the sidecar payloads should be shared between caller and the RPC
> layer, so really it's the new {{RpcSidecar::FromSlice}} API that causes the
> problems because ownership is not shared with the {{RpcSidecar}} which does
> have the correct lifetime. I propose removing {{FromSlice}} and having a
> {{FromFaststring(shared_ptr<faststring>)}} variant.
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