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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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@harshitkr12 harshitkr12 commented Dec 15, 2025 •
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Summary:

Why ?
When uploading blobs to Azure Storage over HTTPS (SSL/TLS), curl_easy_send() can return CURLE_OK with 0 bytes sent. This would lead to a retry without delay immediately, causing a tight CPU-spinning loop.

What ?
Added a 10ms sleep when curl_easy_send() returns CURLE_OK with 0 bytes sent to prevent rapid retries and allow the OS scheduler to run other threads.

Test Plan:

cmake --build .
ctest -R "azure-core" --output-on-failure
>> 100% tests passed, 0 tests failed out of 459

@github-actions github-actions bot added Azure.Core Community Contribution Community members are working on the issue customer-reported Issues that are reported by GitHub users external to the Azure organization. labels Dec 15, 2025
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github-actions bot commented Dec 15, 2025

Thank you for your contribution @harshitkr12! We will review the pull request and get back to you soon.

@harshitkr12 harshitkr12 changed the title Fix CPU spinning when curl_easy_send returns 0 bytes on SSL socket wr… Fix CPU spinning when curl_easy_send returns 0 bytes on SSL socket writes Dec 15, 2025
ashu-tripathi-rubrik
ashu-tripathi-rubrik reviewed Dec 15, 2025
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sdk/core/azure-core/src/http/curl/curl.cpp
// without making progress. This allows the scheduler to run other threads.
std::this_thread::sleep_for(std::chrono::milliseconds(10));
} else {
sentBytesTotal += sentBytesPerRequest;
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@ashu-tripathi-rubrik ashu-tripathi-rubrik Dec 15, 2025

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Given that the else case is only avoiding the 0 case anyways, might be easier (for code readability purposes), to omit this else part alltogether.

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@RickWinter RickWinter Awaiting requested review from RickWinter RickWinter is a code owner

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Azure.Core Community Contribution Community members are working on the issue customer-reported Issues that are reported by GitHub users external to the Azure organization.

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