> Since JDK13, executing commands in a sub-process defaults to the so called
> `POSIX_SPAWN` launching mechanism (i.e.
> `-Djdk.lang.Process.launchMechanism=POSIX_SPAWN`) on Linux. This works by
> using `posix_spawn(3)` to firstly start a tiny helper program called
> `jspawnhelper` in a subprocess. In a second step, `jspawnhelper` reads the
> command data from the parent Java process over a Unix pipe and finally
> executes (i.e. `execvp(3)`) the requested command.
>
> In cases where the parent process terminates abnormally before `jspawnhelper`
> has read all the expected data from the pipe, `jspawnhelper` will block
> indefinitely on the reading end of the pipe. This is especially harmful if
> the parent process had open sockets, because in that case, the forked
> `jspawnhelper` process will inherit them and keep all the corresponding ports
> open effectively preventing other processes to bind to them. Notice that this
> is not an abstract scenario. We've observed this regularly in production with
> services which couldn't be restarted after a crash after migrating to JDK 17.
>
> The fix of the issue is rather trivial. `jspawnhelper` has to close its
> writing end of the pipe which connects it with the parent Java process
> *before* starting to read from that pipe such that reads from the pipe can
> immediately return with EOF if the parent process terminates abnormally.
>
> Also did some cleanup:
> - in `jspawnhelper.c` correctly chek the result of `readFully()`
> - in `ProcessImpl_md.c` use `restartableWrite()` instead of `write()` to
> write the command data from the parent process to `jspawnhelper`
> - in `childproc.{c,h}` remove remaining traces of `MODE_CLONE` because
> that's long gone.
Volker Simonis has updated the pull request incrementally with one additional
commit since the last revision:
Fix the case of truncated writes in the parent process and add a test for it
-------------
Changes:
- all: https://git.openjdk.org/jdk/pull/13956/files
- new: https://git.openjdk.org/jdk/pull/13956/files/facbdcf3..b41604ae
Webrevs:
- full: https://webrevs.openjdk.org/?repo=jdk&pr=13956&range=05
- incr: https://webrevs.openjdk.org/?repo=jdk&pr=13956&range=04-05
Stats: 123 lines in 5 files changed: 96 ins; 10 del; 17 mod
Patch: https://git.openjdk.org/jdk/pull/13956.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/13956/head:pull/13956
PR: https://git.openjdk.org/jdk/pull/13956
