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Document sequence numbers and generation numbers better

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This commit is contained in:
Markus Armbruster 2011-04-11 21:21:19 +02:00
parent 12a0279a80
commit 47b68a1c1f
1 changed files with 16 additions and 1 deletions
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17
src/lib/common/file.c
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@ -29,7 +29,7 @@
* Known contributors to this file: * Known contributors to this file:
* Dave Pare, 1989 * Dave Pare, 1989
* Steve McClure, 2000 * Steve McClure, 2000
* Markus Armbruster, 2005-2009 * Markus Armbruster, 2005-2011
*/ */
#include <config.h> #include <config.h>
@ -336,6 +336,7 @@ ef_ptr(int type, int id)
/* /*
* Read element ID from table TYPE into buffer INTO. * Read element ID from table TYPE into buffer INTO.
* FIXME pass buffer size! * FIXME pass buffer size!
* INTO is marked fresh with ef_mark_fresh().
* Return non-zero on success, zero on failure. * Return non-zero on success, zero on failure.
*/ */
int int
@ -503,6 +504,7 @@ do_write(struct empfile *ep, void *buf, int id, int count)
* cache straight to disk. * cache straight to disk.
* Cannot write beyond the end of fully cached table (flags & EFF_MEM). * Cannot write beyond the end of fully cached table (flags & EFF_MEM).
* Can write at the end of partially cached table. * Can write at the end of partially cached table.
* FROM must be fresh; see ef_make_stale().
* Return non-zero on success, zero on failure. * Return non-zero on success, zero on failure.
*/ */
int int
@ -598,6 +600,8 @@ get_seqno(struct empfile *ep, int id)
* Increment sequence number in BUF, which is about to be written to EP. * Increment sequence number in BUF, which is about to be written to EP.
* Do nothing if table is not EFF_TYPED (it has no sequence number * Do nothing if table is not EFF_TYPED (it has no sequence number
* then). * then).
* Else, BUF's sequence number must match the one in EP's cache. If
* it doesn't, we're about to clobber a previous write.
*/ */
static void static void
new_seqno(struct empfile *ep, void *buf) new_seqno(struct empfile *ep, void *buf)
@ -612,12 +616,22 @@ new_seqno(struct empfile *ep, void *buf)
elt->seqno = old_seqno + 1; elt->seqno = old_seqno + 1;
} }
/*
* Make all copies stale.
* Only fresh copies may be written back to the cache.
* To be called by functions that may yield the processor.
* Writing an copy when there has been a yield since it was read is
* unsafe, because we could clobber another thread's write then.
* Robust code must assume the that any function that may yield does
* yield. Marking copies stale there lets us catch unsafe writes.
*/
void void
ef_make_stale(void) ef_make_stale(void)
{ {
ef_generation++; ef_generation++;
} }
/* Mark copy of an element of table TYPE in BUF fresh. */
void void
ef_mark_fresh(int type, void *buf) ef_mark_fresh(int type, void *buf)
{ {
@ -703,6 +717,7 @@ ef_extend(int type, int count)
/* /*
* Initialize element ID for EP in BUF. * Initialize element ID for EP in BUF.
* FIXME pass buffer size! * FIXME pass buffer size!
* BUF is marked fresh with ef_mark_fresh().
*/ */
void void
ef_blank(int type, int id, void *buf) ef_blank(int type, int id, void *buf)