pgsql: On Windows, syslogger runs in two threads.

Log Message:
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On Windows, syslogger runs in two threads. The main thread processes config
reload and rotation signals, and a helper thread reads messages from the
pipe and writes them to the log file. However, server code isn't generally
thread-safe, so if both try to do e.g palloc()/pfree() at the same time,
bad things will happen. To fix that, use a critical section (which is like
a mutex) to enforce that only one the threads are active at a time.

Tags:
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REL8_2_STABLE

Modified Files:
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    pgsql/src/backend/postmaster:
        syslogger.c (r1.29.2.5 -> r1.29.2.6)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/syslogger.c?r1=1.29.2.5&r2=1.29.2.6)