On Thu, 29 Jan 2026, Andrew Bell via curl-library wrote:
I have an application that is making many http requests through curl. Each request is handled by a thread. On my OS (OSX) there is a default file descriptor limit of 256. When I make a curl request with curl_easy_perform, it creates two pipes in addition to creating the socket on which to make the request. It appears that these pipes are made for communication internal to curl about async DNS resolution. This means that I'm using three file descriptors for each request, which means get "out of file descriptor" errors when my application has ~80 threads making curl requests.
The socketpair file descriptors are however only used while name resolving.
It looks like I can disable async resolution at compile-time, which I would think would eliminate the pipes and associated file descriptors, but I can't control how the library was built for users. I don't see any way I can disable this async resolution at runtime, but perhaps I'm missing something.
Nope. Because using sync name resolving is terrible and is normally only used as a worst-case fallback.
For example: timeouts for sync name resolving is bad, uses signals and is error-prone. It messes up libcurl's ability to work asynchronously.
Does anyone have any ideas/recommendations to eliminate the FDs being used for DNS resolution or some other ideas on how I can reduce the likelihood of running out of FDs when using lots of simultaneous requests?
I would recommend using the multi interface and avoid threads. It probably also increases performance.
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