I have a fairly old version of the protobuf library, so if this has
been changed let me know, but I have a situation where Message::Clear
() is causing my cpu to go to like 70% for an extended period of time.

It's also possible this is user error, so please correct me if that's
the case.

Basically what I have is a top level message with a bunch of optional
messages, which I send across the wire.

One of these optional messages is defined as follows:

message DataChunkList {
    required bool             is_end_of_list = 1;
    repeated DataChunk  data = 2;
};

message DataChunk {
    optional bytes    data = 1;
    //Other fields here
};

The "data" field will almost always be exactly 4k, and I will usually
not want to send 1 chunk at a time, but a list of around 32 at a
time.

So I save an instance of the top level message in the class containing
my sending code, and right before I'm about to send data I do the
following:

net::DataChunkList* pChunks = m_CachedTopLevel.mutable_data_chunk_list
();

//Should already be clear, but just in case
pChunks->Clear();
prevCount = pChunks->mutable_data()->ClearedCount();

for (int i=prevCount; i < num_chunks; ++i)
{
    net::DataChunk* pChunk = new net::DataChunk();
    pChunk->mutable_data()->reserve(4096);
    pChunkList->mutable_data()->AddCleared(pChunk);
}

for (int i=0; i < num_chunks; ++i)
{
   net::DataChunk* pChunk = pChunks->mutable_data()->ReleaseCleared();
   pChunk->mutable_data()->assign(global_4k_buffer, 4096);
   pChunks->mutable_data()->AddAllocated(pChunks);
}

send(m_CachedTopLevel);

m_CachedTopLevel.Clear();





I ran a profiler on my code, and the very last line  (the Clear())
takes up almost 95% of the CPU usage for the function, and the
function takes up about about 30% of the CPU usage of the entire app.
So obviously this is a big problem.

The comment on the code says that clear "does not free any memory"
however.  So why could it be using so much CPU?  Am I misunderstanding
the purpose / usage of these methods?  What I'm trying to do is just
re-use a pool of 4k buffers for all of these sends.
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