Re: 2pc leaks fds

Concretely, I propose to have a new struct like

typedef struct xlogReaderFuncs
{
    XLogPageReadCB read_page;
    XLogSegmentOpenCB open_segment;
    XLogSegmentCloseCB open_segment;
} xlogReaderFuncs;

#define XLOGREADER_FUNCS(...) &(xlogReaderFuncs){__VA_ARGS__}

and then invoke it something like

    xlogreader = XLogReaderAllocate(wal_segment_size, NULL,
                                    XLOGREADER_FUNCS(.readpage = &read_local_xlog_page,
                                              .opensegment = &wal_segment_open),
                                              .closesegment = &wal_segment_close),
                                    NULL);

(with suitable definitions for XLogSegmentOpenCB etc) so that the
support functions are all available at the xlogreader level, instead of
"open" being buried at the read-page level.  Any additional support
functions can be added easily.

This would give xlogreader a simpler interface.

If people like this, I could make this change for pg13 and avoid
changing the API again in pg14.

Thougths?

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
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