Exceeding the max. number of pending aio requests on MacOS

[edgargabriel]

Thank you for taking the time to submit an issue!

Background information

This is a bug discovered while debugging issue #8350 Running our testsuite on Mac OS revealed that posted a large number of non-blocking read/write operations leads to an error message on this platform. A fix is already available and will be committed shortly.

What version of Open MPI are you using? (e.g., v3.0.5, v4.0.2, git branch name and hash, etc.)

master, 4.0.x, 4.1.x

Describe how Open MPI was installed (e.g., from a source/distribution tarball, from a git clone, from an operating system distribution package, etc.)

git clone

If you are building/installing from a git clone, please copy-n-paste the output from git submodule status.

all looks good.

Please describe the system on which you are running

• Operating system/version:
• Computer hardware:
• Network type:

MacOS

Details of the problem

This is a bug discovered while debugging issue #8350 Running our testsuite on Mac OS revealed that posted a large number of non-blocking read/write operations leads to an error message on this platform. A fix is already available and will be committed shortly.

The issue stems from limitations on macOs and the concurrent number of aio_read/aio_write operations that can be pending. While the code already handled that correctly for a single request, this bug exposed that the overall limited has to be respected across all pending requests.