On 12/18/24 07:54, Yu Kuai wrote:
> Hi,
>
> 在 2024/12/17 21:14, Nilay Shroff 写道:
>> This commit helps fix the above race condition by touching a temp file. The
>> the existence of the temp file is then polled by the background process at
>> regular interval. Until the temp file is created, the background process
>> would not forward progress and starts submitting IO and from the main
>> thread we'd touch temp file only after we write PID of the background
>> process into cgroup.procs.
>
> It's right sleep 0.1 is not appropriate here, and this can work.
> However, I think reading cgroup.procs directly is better, something
> like following:
>
> _throtl_test_io() {
> - local pid
> + local pid="none"
>
> {
> local rw=$1
> local bs=$2
> local count=$3
>
> - sleep 0.1
> + while ! cat $CGROUP2_DIR/$THROTL_DIR/cgroup.procs | grep $pid; do
> + sleep 0.1
> _throtl_issue_io "$rw" "$bs" "$count"
> } &
Thank you for your review and suggestion!
However, IMO this may not work always because the issue here's that the @pid is local
variable and when the shell starts the background job/process, typically, all local
variables are copied to the new job. Henceforth, any update made to @pid in the parent
shell would not be visible to the background job.
I think, for IPC between parent shell and background job, we may use temp file,
named pipe or signals. As file is the easiest and simplest mechanism, for this
simple test I preferred using file.
Thanks,
--Nilay
