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Terminate custom module scripts on exit

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(Fixes #358.)

Subprocesses created for custom module scripts were previously left
running when the parent Waybar process exited. This patch sets the
parent-death signal of child processes (PR_SET_PDEATHSIG on Linux,
PROC_PDEATHSIG_CTL on FreeBSD) to SIGTERM.

Caveats:

* This uses Linux-specific or FreeBSD-specific calls. I don’t know if
  this project targets other systems?
* There is a possibility that Waybar exits after calling `fork()`, but
  before calling `prctl` to set the parent-death signal. In this case,
  the child will not receive the SIGTERM signal and will continue to
  run. I did not handle this case as I consider it quite unlikely, since
  module scripts are usually launched only when Waybar starts. Please
  let me know if you think it needs to be handled.

Testing:

* With `htop` open, run Waybar v0.9.5 with a custom module that has an
  `exec` script. Terminate the Waybar process and notice that the
  script’s subprocess stays alive and is now a child of the init
  process.
* Run Waybar with this patch and follow the same steps as above. Notice
  that this time the script’s subprocess terminates when the parent
  exits.
This commit is contained in:
Mattéo Delabre 2021-02-12 20:15:38 +01:00
parent 08e19602f7
commit d8706af2ea
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GPG Key ID: AE3FBD02DC583ABB
1 changed files with 19 additions and 0 deletions
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19
include/util/command.hpp
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@ -5,6 +5,13 @@
#include <sys/wait.h>
#include <unistd.h>
#ifdef __linux__
#include <sys/prctl.h>
#endif
#ifdef __FreeBSD__
#include <sys/procctl.h>
#endif
#include <array>
extern std::mutex reap_mtx;
@ -77,6 +84,18 @@ inline FILE* open(const std::string& cmd, int& pid) {
// Reset sigmask
err = pthread_sigmask(SIG_UNBLOCK, &mask, nullptr);
if (err != 0) spdlog::error("pthread_sigmask in open failed: {}", strerror(err));
// Kill child if Waybar exits
int deathsig = SIGTERM;
#ifdef __linux__
if (prctl(PR_SET_PDEATHSIG, deathsig) != 0) {
spdlog::error("prctl(PR_SET_PDEATHSIG) in open failed: {}", strerror(errno));
}
#endif
#ifdef __FreeBSD__
if (procctl(P_PID, 0, PROC_PDEATHSIG_CTL, reinterpret_cast<void*>(&deathsig)) == -1) {
spdlog::error("procctl(PROC_PDEATHSIG_CTL) in open failed: {}", strerror(errno));
}
#endif
::close(fd[0]);
dup2(fd[1], 1);
setpgid(child_pid, child_pid);