bitcoind throw error `Cannot create connection` if there are more than 1024 cocurrent connections #18158

Bitcoind throw an error:

Cannot create connection: non-selectable socket created (fd >= FD_SETSIZE ?)

Expected behavior

Should not display this error.

To reproduce Before start bitcoind, set fd limit to 10240

ulimit -n 10240

Then start bitcoind with -rpcworkqueue=10240 parameter. Start to send over 1024 requests to RPC on the same time.

bitcoind version is 0.17.0, OS is Linux.

Possiable Cause I have check the code, if a socket is !IsSelectableSocket(), bitcoind then print this error. Then I check IsSelectableSocket function in src/compat.h, I found IsSelectableSocket() may return ( fd < FD_SETSIZE) as return value if OS is not Linux. This is strange while I am using Linux. I think the __linux__ macro is not defined on compiling, but I cant verify that. The binary file from official site.

I think this is not a bug: https://github.com/bitcoin/bitcoin/blob/94c0287aec9a250f58c4c633dabaf405d82cecd2/src/compat.h#L20-L23

@hebasto Why do you think this is not a bug? Right below, IsSelectableSocket should be return true on linux, and the reporter says they are using the release binaries on linux. This sounds like it is not correctly using poll anymore, which would be pretty bad.

bitcoind version is 0.17.0, OS is Linux.

That is a fairly old version, I'm doubtful anyone is too interested in reports on versions that old, though the code looks the same in current versions... this behaviour could change due to build system differences.

Several other parts of the codebase also use "__linux__".

@greensea

bitcoind version is 0.17.0, OS is Linux. The binary file from official site.

Which of the following?

bitcoin-0.17.0-aarch64-linux-gnu.tar.gz            03-Oct-2018 09:12            27078635
bitcoin-0.17.0-arm-linux-gnueabihf.tar.gz          03-Oct-2018 09:12            24306360
bitcoin-0.17.0-i686-pc-linux-gnu.tar.gz            03-Oct-2018 09:13            30680891
bitcoin-0.17.0-x86_64-linux-gnu.tar.gz             03-Oct-2018 09:15            28262892

I am using this one: https://bitcoin.org/bin/bitcoin-core-0.17.0.1/bitcoin-0.17.0.1-x86_64-linux-gnu.tar.gz

I just noticed 0.19 is released, I will upgrade my binary to 0.19 and check if this error still exists. I will report the result later.

After upgrade to 0.19.0.1, this error never occurs. Maybe there is a compile mistake in 0.17.0.1 binary? Anyway, version 0.19.0.1 works perfectly now.

Is it worth adding to bitcoind and bitcoin-qt ability to provide a user with compiling flags info (or some important ones of them), e.g., to the debug.log file (smth like #17826) ?

I think this can be closed?

Yeah, looks like this was fixed in 0.19 onward, based on the last comment by the reporter?