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Provide a reliable mechanism for terminating a background worker.

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Although previously-introduced APIs allow the process that registers a
background worker to obtain the worker's PID, there's no way to prevent
a worker that is not currently running from being restarted.  This
patch introduces a new API TerminateBackgroundWorker() that prevents
the background worker from being restarted, terminates it if it is
currently running, and causes it to be unregistered if or when it is
not running.

Patch by me.  Review by Michael Paquier and KaiGai Kohei.
This commit is contained in:
Robert Haas
2013-10-18 10:21:25 -04:00
parent c2316dcda1
commit 523beaa11b
5 changed files with 96 additions and 19 deletions
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19
doc/src/sgml/bgworker.sgml
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@ -184,13 +184,18 @@ typedef struct BackgroundWorker
argument to <function>RegisterDynamicBackgroundWorker</function>. If the
worker is successfully registered, this pointer will be initialized with an
opaque handle that can subsequently be passed to
<function>GetBackgroundWorkerPid(<parameter>BackgroundWorkerHandle *</parameter>, <parameter>pid_t *</parameter>)</function>.
This function can be used to poll the status of the worker: a return
value of <literal>BGWH_NOT_YET_STARTED</> indicates that the worker has not
yet been started by the postmaster; <literal>BGWH_STOPPED</literal>
indicates that it has been started but is no longer running; and
<literal>BGWH_STARTED</literal> indicates that it is currently running.
In this last case, the PID will also be returned via the second argument.
<function>GetBackgroundWorkerPid(<parameter>BackgroundWorkerHandle *</parameter>, <parameter>pid_t *</parameter>)</function> or
<function>TerminateBackgroundWorker(<parameter>BackgroundWorkerHandle *</parameter>)</function>.
<function>GetBackgroundWorker</> can be used to poll the status of the
worker: a return value of <literal>BGWH_NOT_YET_STARTED</> indicates that
the worker has not yet been started by the postmaster;
<literal>BGWH_STOPPED</literal> indicates that it has been started but is
no longer running; and <literal>BGWH_STARTED</literal> indicates that it is
currently running. In this last case, the PID will also be returned via the
second argument.
<function>TerminateBackgroundWorker</> causes the postmaster to send
<literal>SIGTERM</> to the worker if it is running, and to unregister it
as soon as it is not.
</para>
<para>