[PATCH] lock_timeout and common SIGALRM framework

Hi,

attached is a patch to implement a framework to simplify and
correctly nest multiplexing more than two timeout sources
into the same SIGALRM signal handler.

The framework is using a new internal API for timeouts:

bool enable_timeout(TimeoutName tn, int delayms);
bool disable_timeout(TimeoutName tn, bool keep_indicator);
bool disable_all_timeouts(bool keep_indicators);

A timeout source has these features to allow different initialization,
cleanup and check functions and rescheduling:

typedef void (*timeout_init)(TimestampTz, TimestampTz);
typedef void (*timeout_destroy)(bool);
typedef bool (*timeout_check)(void);
typedef TimestampTz (*timeout_start)(void);

typedef struct {
         TimeoutName     index;
         bool            resched_next;
         timeout_init    timeout_init;
         timeout_destroy timeout_destroy;
         timeout_check   timeout_check;
         timeout_start   timeout_start;
         TimestampTz     fin_time;
} timeout_params;

This makes it possible to differentiate between the standby and
statement timeouts, regular deadlock and standby deadlock using
the same signal handler function.

And finally, this makes it possible to implement the lock_timeout
feature that we at Cybertec implemented more than 2 years ago.

The patch also adds two new tests into prepared_xacts.sql to trigger
the lock_timeout instead of statement_timeout.

Documentation and extensive comments are included.

Best regards,
Zoltán Böszörményi

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Zoltán Böszörményi
Cybertec Schönig&  Schönig GmbH
Gröhrmühlgasse 26
A-2700 Wiener Neustadt, Austria
Web: http://www.postgresql-support.de
      http://www.postgresql.at/