Github user HyukjinKwon commented on a diff in the pull request: https://github.com/apache/spark/pull/18320#discussion_r122695789 --- Diff: R/pkg/inst/worker/daemon.R --- @@ -31,7 +31,30 @@ inputCon <- socketConnection( port = port, open = "rb", blocking = TRUE, timeout = connectionTimeout) while (TRUE) { - ready <- socketSelect(list(inputCon)) + ready <- socketSelect(list(inputCon), timeout = 1) + + # Note that the children should be terminated in the parent. If each child terminates + # itself, it appears that the resource is not released properly, that causes an unexpected + # termination of this daemon due to, for example, running out of file descriptors + # (see SPARK-21093). Therefore, the current implementation tries to retrieve children + # that are exited (but not terminated) and then sends a kill signal to terminate them properly + # in the parent. + # + # There are two paths that it sends a signal to terminate the children in the parent. + # + # 1. Every second if any socket connection is not available. + # 2. Right after a socket connection is available. + # + # In other words, the parent sends the signal to children every second or right before + # launching other worker children from the following new socket connection. + # + # Only the process IDs of exited children are returned and the termination is attempted below. + finishedChildren <- parallel:::selectChildren(timeout = 0) --- End diff -- This is 0 by default but I added to prevent conversion.
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