Elixir/Ports and external process wiring: Difference between revisions

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== Shimming can kill ==

It's possible to write a small adapter which is sensitive to stdin closing, then converts this into a stronger signal like SIGTERM which it forwards to its own child. This is the idea behind a suggested shell script<ref>https://hexdocs.pm/elixir/1.19.0/Port.html#module-orphan-operating-system-processes</ref> for Elixir and the erlexec<ref>[https://hexdocs.pm/erlexec/readme.html https://hexdocs.pm/erlexec/]</ref> library. The opposite adapter is also found in the [[w:nohup|nohup]] shell command and the grimsby<ref>https://github.com/shortishly/grimsby</ref> library: these will keep standard in or out open for the child process even after the parent exits.

It's possible to write a small adapter which is sensitive to stdin closing, then converts this into a stronger signal like SIGTERM which it forwards to its own child. This is the idea behind a suggested shell script<ref>https://hexdocs.pm/elixir/1.19.0/Port.html#module-orphan-operating-system-processes</ref> for Elixir and the erlexec<ref>[https://hexdocs.pm/erlexec/readme.html https://hexdocs.pm/erlexec/]</ref> library. The opposite adapter is also found in the [[w:nohup|nohup]] shell command and the grimsby<ref>https://github.com/shortishly/grimsby</ref> library: these will keep standard in and/or standard out open for the child process even after the parent exits.

I took ~~this~~ approach with my rsync library and included a small C program<ref>https://gitlab.com/adamwight/rsync_ex/-/blob/main/src/main.c?ref_type=heads</ref> which wraps rsync and makes it sensitive to the BEAM port_close. It's featherweight, leaving pipes unchanged as it passes control to rsync—its only real effect is to convert SIGHUP to SIGKILL (see the sidebar discussion of different signals below).

I took the shim approach with my rsync library and included a small C program<ref>https://gitlab.com/adamwight/rsync_ex/-/blob/main/src/main.c?ref_type=heads</ref> which wraps rsync and makes it sensitive to the BEAM port_close. It's featherweight, leaving pipes unchanged as it passes control to rsync—its only real effect is to convert SIGHUP to SIGKILL (but should have been SIGTERM, see the sidebar discussion of different signals below).

== Reliable clean up ==

@@ Line 107: / Line 107: @@
 == Shimming can kill ==
-It's possible to write a small adapter which is sensitive to stdin closing, then converts this into a stronger signal like SIGTERM which it forwards to its own child.  This is the idea behind a suggested shell script<ref>https://hexdocs.pm/elixir/1.19.0/Port.html#module-orphan-operating-system-processes</ref> for Elixir and the erlexec<ref>[https://hexdocs.pm/erlexec/readme.html https://hexdocs.pm/erlexec/]</ref> library.  The opposite adapter is also found in the [[w:nohup|nohup]] shell command and the grimsby<ref>https://github.com/shortishly/grimsby</ref> library: these will keep standard in or out open for the child process even after the parent exits.
+It's possible to write a small adapter which is sensitive to stdin closing, then converts this into a stronger signal like SIGTERM which it forwards to its own child.  This is the idea behind a suggested shell script<ref>https://hexdocs.pm/elixir/1.19.0/Port.html#module-orphan-operating-system-processes</ref> for Elixir and the erlexec<ref>[https://hexdocs.pm/erlexec/readme.html https://hexdocs.pm/erlexec/]</ref> library.  The opposite adapter is also found in the [[w:nohup|nohup]] shell command and the grimsby<ref>https://github.com/shortishly/grimsby</ref> library: these will keep standard in and/or standard out open for the child process even after the parent exits.
-I took this approach with my rsync library and included a small C program<ref>https://gitlab.com/adamwight/rsync_ex/-/blob/main/src/main.c?ref_type=heads</ref> which wraps rsync and makes it sensitive to the BEAM port_close.  It's featherweight, leaving pipes unchanged as it passes control to rsync—its only real effect is to convert SIGHUP to SIGKILL (see the sidebar discussion of different signals below).
+I took the shim approach with my rsync library and included a small C program<ref>https://gitlab.com/adamwight/rsync_ex/-/blob/main/src/main.c?ref_type=heads</ref> which wraps rsync and makes it sensitive to the BEAM port_close.  It's featherweight, leaving pipes unchanged as it passes control to rsync—its only real effect is to convert SIGHUP to SIGKILL (but should have been SIGTERM, see the sidebar discussion of different signals below).
 == Reliable clean up ==