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Fix CPU spinning when curl_easy_send returns 0 bytes on SSL socket writes #6890

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Fix CPU spinning when curl_easy_send returns 0 bytes on SSL socket writes #6890

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10 changes: 10 additions & 0 deletions sdk/core/azure-core/src/http/curl/curl.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -624,6 +624,9 @@ CURLcode CurlConnection::SendBuffer(
// expected to return CURLE_AGAIN (since socket is ready), so, a chuck of data will be uploaded
// and result will be CURLE_OK which breaks the loop. Also, getting other than CURLE_OK or
// CURLE_AGAIN throws.
// NOTE: curl_easy_send() may return CURLE_OK with sentBytesPerRequest == 0 on SSL sockets
// when the socket is not ready for writing. In this case, we add a small delay to prevent
// busy-wait loops and allow the scheduler to release the current quantum.
context.ThrowIfCancelled();
for (CURLcode sendResult = CURLE_AGAIN; sendResult == CURLE_AGAIN;)
{
Expand All @@ -637,6 +640,13 @@ CURLcode CurlConnection::SendBuffer(
switch (sendResult)
{
case CURLE_OK: {
if (sentBytesPerRequest == 0)
{
// When curl_easy_send returns CURLE_OK but sends 0 bytes (which can happen on SSL
// sockets), add a small delay to prevent rapid retries that keep the CPU busy
// without making progress. This allows the scheduler to run other threads.
std::this_thread::sleep_for(std::chrono::milliseconds(10));
}
sentBytesTotal += sentBytesPerRequest;
break;
}
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