Various bug fixes throughout the code base #171
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iCharlesHu
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| int flags = fcntl(fd, F_GETFD); | ||
| if (flags >= 0) { | ||
| // Set FD_CLOEXEC on every open fd so they are closed after exec() | ||
| fcntl(fd, F_SETFD, flags | FD_CLOEXEC); |
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If you're doing a syscall anyway, why don't you just close it?
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For two reasons:
- I've searched around (close vs setting FD_CLOEXEC) and it seems in general
FD_CLOEXECis preferred for this situation:
https://utcc.utoronto.ca/~cks/space/blog/unix/ForkFDsAndRaces
- A more practical reason is I don't think we can safely
close()while traversing/dev/fdbeforeclose()modifies that directory.
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I've searched around (close vs setting FD_CLOEXEC) and it seems in general FD_CLOEXEC is preferred for this situation:
Both of those articles I think are really talking about the pre-fork case. I think in our specific situation where we've already called fork (and thus have exactly one thread and no concurrency considerations), and we can guarantee that we will not call fork again, and that we will call exec imminently, there's no practical difference (that I can see).
A more practical reason is I don't think we can safely close() while traversing /dev/fd before close() modifies that directory.
This seems like a great point though!
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A more practical reason is I don't think we can safely close() while traversing /dev/fd before close() modifies that directory.
That should not happen and doesn't happen in the original code from swift-sdk-generator. How the original code works is:
- Get the maximum fd
- Loop from 3 to maximum fd and close
That's completely fine. What is not fine (but that's not what the original code does) is to close whilst iterating of course.
| for (int fd = STDERR_FILENO + 1; fd <= highest_open_fd; fd++) { | ||
| // We must NOT close pipefd[1] for writing errors | ||
| if (fd != pipefd[1]) { | ||
| close(fd); |
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close feels better here and will be cheaper overall. Otherwise you need to do N syscalls to mark as CLOEXEC and later on there's more work necessary to close them. Why not just close?
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Ditto to above: it seems the general consensus is to use FD_CLOEXEC instead of close(). We would have to issue N close() calls here, so without close_range, it doesn't really save much.
- Instead of calling `[UInt8].removeFirst` on `LineSequence`’s `underlyingBuffer`, we now use an index-based approach. This change improves overall streaming performance by eliminating the `O(n)` `.removeFirst()` operation. - The `safelyCloseMultiple` function has been updated to handle cases where the same `IODescriptor` is passed to multiple input/outputs. - On Linux, `_highest_possibly_open_fd_dir_linux()` has been updated to `_close_open_fd_linux()` to more efficiently emulate `POSIX_SPAWN_CLOEXEC_DEFAULT`.
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[UInt8].removeFirstonLineSequence’sunderlyingBuffer, we now use an index-based approach. This change improves overall streaming performance by eliminating theO(n).removeFirst()operation.safelyCloseMultiplefunction has been updated to handle cases where the sameIODescriptoris passed to multiple input/outputs._highest_possibly_open_fd_dir_linux()has been updated to_close_open_fd_linux()to more efficiently emulatePOSIX_SPAWN_CLOEXEC_DEFAULT.Resolves: #165, #160, #159