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https://issues.apache.org/jira/browse/KUDU-2011?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16011342#comment-16011342
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Henry Robinson commented on KUDU-2011:
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That's a bit awkward in the timeout case because it forces a reallocation
(which, if you're setting aggressive timeouts, you might particularly want to
avoid). If you want to do some accounting after releasing the buffers, this API
makes it hard to do as well. We could make {{ReleaseSidecars()}} blocking or
with a timeout, so that there's a way to be sure that the buffers are done with.
> 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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