On 4/25/17 9:15 PM, Vincent Lefevre wrote:
> On 2017-04-25 23:49:56 +0200, Jilles Tjoelker wrote:
>> On Tue, Apr 25, 2017 at 03:21:24PM +0200, Vincent Lefevre wrote:
>>> I wonder how the following script is supposed to behave.
>>> The POSIX spec seems ambiguous about SIGCHLD trap in a shell. It says:
>>> "[...] a signal specified using a symbolic name, without the SIG prefix,
>>> as listed in the tables of signal names in the <signal.h> header defined
>>> in XBD Headers"; there, SIGCHLD is listed as "Child process terminated,
>>> stopped, [XSI] or continued". From this spec, I would assume that the
>>> trap would be executed for any child process that terminates, stops, or
>>> continues. But this is not what I observe.
>> I would not assume that. Since trap actions are not executed while
>> waiting for a foreground process to exit, it is likely that multiple
>> instances of SIGCHLD will be coalesced into a single trap action
>> execution.
> IMHO, this would be a bug. A shell should be able to know when all
> its children have terminated. IMHO, all the pending traps should
> be executed before the next command.

There is no requirement that a trap be executed each time a particular
signal is generated.  There is no requirement that the system keep a
count of instances of a particular pending signal; only that the signal
is pending.  SIGCHLD isn't different from any other signal in this

``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    c...@case.edu    http://cnswww.cns.cwru.edu/~chet/

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