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make managing multiprocess services easier and safer #16

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merged 4 commits into from Mar 25, 2014

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@acg @bruceg
@acg
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acg commented Mar 24, 2014

These changes make managing multiprocess services with daemontools-encore easier and safer. An example of a multiprocess service is one with a long-running shell pipeline in its ./run file.

Multiprocess services were problematic for classic daemontools, and are still somewhat problematic for daemontools-encore. Prior to this change, signalling multiprocess services under the latter could result in orphaned processes, unclean system shutdown, and problems with ^Z and ^C when running in a foreground terminal. These issues are addressed by propagating certain signals to services, and by signalling the entire process group when a service uses setsid.

This change also introduces compatibility with classic daemontools, which did not use a new process group for each service. To avoid using a new process group for a service, create a file ./no-setsid in the service directory. To explicitly signal just the process leader of a setsid service, use svc -+. To explicitly signal the entire process group of a no-setsid service, use svc -=.

This change is a refactor and rebase of #3. (You may find some more information there.)

acg added some commits Mar 24, 2014

@acg
disable setsid per-service with a ./no-setsid file. 
Before this change, each service always ran in a separate process group via setsid(2). For users that need the classic daemontools behavior instead, the existence of a file ./no-setsid in a service directory will disable this.
302f429
@acg
when using setsid, signal the entire process group. 
Prior to this change, only the process leader of a service would be signalled by svc(8). For multiprocess services, this meant that sending SIGINT or SIGTERM would typically orphan processes. Better behavior: always signal the entire process group when a service is using setsid.
68f1388
@acg
ensure clean service shutdown and clean ^C, ^Z behavior. 
When supervise(8) itself receives certain signals, they should be propagated to the service.

When supervise(8) receives SIGTERM or SIGINT, propagate this to the supervised process by behaving as if `svc -dx` had been called. SIGTERM occurs during system shutdown. SIGINT can occur when svscan(8) is running in terminal foreground and gets ^C. In both cases, not propagating the signal to a setsid service will result in orphans that continue to run.

When supervise(8) receives SIGTSTOP, for example because svscan(8) is running in terminal foreground and gets ^Z, behave as if `svc -p` had been called. Similarly, when supervise(8) receives SIGCONT, behave as if `svc -c` had been called. This ensures that setsid services stop and resume when running in foreground.
4cc51d7
@acg
disable process group signaling with `svc -=`. 
To explicitly send signals only to the process group leader of a service, even if the service uses setsid, use `svc -=`.

To explicitly send signals to the entire process group, even if the service uses ./no-setsid, use `svc -+`.

Otherwise, process group signalling is used iff the service is setsid.
a7b641d

@acg acg referenced this pull request Mar 24, 2014

Closed

optionally setsid and transparently use process group control #3

bruceg added a commit that referenced this pull request Mar 25, 2014

@bruceg
Merge pull request #16 from acg/multiprocess-services 
make managing multiprocess services easier and safer
1c95026

@bruceg bruceg merged commit 1c95026 into bruceg:master Mar 25, 2014

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