PFS_ringbuffer_index Class Reference

Index in the error-log ring-buffer. More...

#include <cursor_by_error_log.h>

Public Member Functions
void	reset ()
	Reset index. More...
	PFS_ringbuffer_index ()
	Constructor. More...
void	set_at (const PFS_ringbuffer_index *other)
	Set this index to a given position. More...
void	set_after (const PFS_ringbuffer_index *other)
	Set our index to the element after the given one (if that is valid; otherwise, we cannot determine a next element). More...
log_sink_pfs_event *	get_event ()
	Get event if it's still valid. More...
log_sink_pfs_event *	scan_next ()
	Return current record (if valid), then set index to the next record. More...

Private Attributes
int	m_index
	Numeric row index. More...
log_sink_pfs_event *	m_event
	Pointer to an event in the ring-buffer. More...
ulonglong	m_timestamp
	Time-stamp we copied from the event we point to when setting this index. More...

Detailed Description

Index in the error-log ring-buffer.

Has a numeric index, a pointer to an event in the buffer, and the timestamp for that event. This lets us easily check whether this index is still valid: its timestamp must be greater than or equal to that of the ring-buffer's oldest entry (the tail or "read-position"). If our timestamp is older than that value, it points to an event that has since expired.

Constructor & Destructor Documentation

PFS_ringbuffer_index()

PFS_ringbuffer_index::PFS_ringbuffer_index ( )

inline

Constructor.

Member Function Documentation

get_event()

log_sink_pfs_event * PFS_ringbuffer_index::get_event ( )

inline

Get event if it's still valid.

Caller should hold read-lock on ring-buffer.

If m_index is 0, the index was reset, and we re-obtain the ring-buffer's read-pointer / tail. This updates m_event and m_timestamp.

If m_index is -1 (EOF), we return nullptr.

Otherwise, we try to obtain the event in the ring-buffer pointed to by m_event. If that event is still valid, we return it; otherwise, we return nullptr (but leave the stale pointer on the object for debugging). It is therefore vital to to determine success/failure by checking the retval rather than calling this method and then checking m_event directly!

Return values

nullptr	no event (EOF, empty buffer, or stale index)
!=nullptr	the event this index is referring to

reset()

void PFS_ringbuffer_index::reset ( void  )

inline

Reset index.

scan_next()

log_sink_pfs_event * PFS_ringbuffer_index::scan_next ( )

inline

Return current record (if valid), then set index to the next record.

Caller should hold read-lock on ring-buffer. Returned value is only valid as long as the lock is held.

Note that three states are possible: a) an event-pointer is returned, and the index points to a valid succeeding event (i.e. is not EOF): there are more elements b) an event-pointer is returned, but the index now flags EOF: this was the last element c) NULL is returned, and the index flags EOF: no event could be obtained (the buffer is empty, or we're at EOF)

Updates m_event, m_timestamp, and m_index.

Return values

nullptr	no valid record could be obtained (end of buffer etc.)
!=nullptr	pointer to an entry in the ring-buffer

set_after()

void PFS_ringbuffer_index::set_after ( const PFS_ringbuffer_index *  other )

inline

Set our index to the element after the given one (if that is valid; otherwise, we cannot determine a next element).

Caller should hold read-lock on ring-buffer.

Parameters

other

set our index to the position after the given one

set_at()

void PFS_ringbuffer_index::set_at ( const PFS_ringbuffer_index *  other )

inline

Set this index to a given position.

This copies other without validating it.

Parameters

other

set our index from the given one

Member Data Documentation

m_event

log_sink_pfs_event* PFS_ringbuffer_index::m_event

private

Pointer to an event in the ring-buffer.

Before dereferencing this pointer, use

See also

log_sink_pfs_event_valid() to make sure it has not become stale.

m_index

int PFS_ringbuffer_index::m_index

private

Numeric row index.

valid range [0;num_events[. -1 == EOF

m_timestamp

ulonglong PFS_ringbuffer_index::m_timestamp

private

Time-stamp we copied from the event we point to when setting this index.

The ring-buffer keeps track of what the oldest item in it is. If our timestamp is older than that item's timestamp, the event we're pointing too has been purged from the ring-buffer, and our pointer is stale. 0 for undefined.

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The documentation for this class was generated from the following file:

• storage/perfschema/cursor_by_error_log.h