Additional context I forgot to include. I'm getting identical output with
just a naive capnp::writeMessageToFd on the original builder. In the sample
I'm looking at I only ever write 1 message. The conversion using the capnp
decode tool fails with:
*** ERROR CONVERTING PREVIOUS MESSAGE ***
The following error occurred while converting the message above.
This probably means the input data is invalid/corrupted.
Exception description: expected ref->kind() == WirePointer::STRUCT; Message
contains non-struct pointer where struct pointer was expected.
Code location: capnp/layout.c++:2168
*** END ERROR ***
On Tue, May 12, 2020 at 5:38 PM Vitali Lovich <vlov...@gmail.com> wrote:
> I'm having a weird problem that I'm suspecting comes from invalid usage of
> the API?
> Basically I offload the serialized message (obtained via
> capnp::messageToFlatArray) to a background thread for appending to a file.
> However, I'm noticing that the messages are corrupt. I'm wondering if I'm
> misusing the API in some obvious way? AFAICT writing the output of
> messageToFlatArray should be identical to sending it to an OutputStream...
>
> Hopefully it's not a glaring oversight on my part like the past couple of
> messages.
>
> Pseudo-code below:
>
> void append(capnp::MessageBuilder& builder) {
> auto serializedInWords = capnp::messageToFlatArray(builder);
> {
> std::lock_guard lg(mutex_);
> queue_.emplace_back(kj::mv(serializedInWords));
> }
> available_.notify_all();
> }
>
> void flushThread() {
> std::vector<kj::Array<const capnp::word>> toFlush;
>
> // output_ is kj::AutoCloseFd - the thread RAII joins on destruction &
> is declared after output_ so the I/O should outlive
> // also the problematic message is one that I write once on start & the
> I/O gets terminated much later so I don't think it's a race for the I/O.
> kj::FdOutputStream output(output_.get());
>
> do {
> {
> std::unique_lock lck(available_);
> available_.wait(lck, [&] { return terminated_ || !queue_.empty());
> toFlush = std::move(queue_);
> }
> for (const auto& message : toFlush) {
> auto messageBytes = message.asBytes();
> output.write(messageBytes.begin(), messageBytes.size());
> }
> } while (!terminated_);
> }
>
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