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Add data structure description comments to memjournal.c. (CVS 5847)

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FossilOrigin-Name: e9c2adbcbf5c28837b06e0fbba93f1764cc3607f
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drh
2008-10-28 18:12:36 +00:00
parent 0f3f072d9f
commit 27c3bd7b73
3 changed files with 36 additions and 19 deletions
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39
src/memjournal.c
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@@ -1,5 +1,5 @@
/*
** 2007 August 22
** 2008 October 7
**
** The author disclaims copyright to this source code. In place of
** a legal notice, here is a blessing:
@@ -10,32 +10,51 @@
**
*************************************************************************
**
** @(#) $Id: memjournal.c,v 1.1 2008/10/17 19:13:05 danielk1977 Exp $
** This file contains code use to implement an in-memory rollback journal.
** The in-memory rollback journal is used to journal transactions for
** ":memory:" databases and when the journal_mode=MEMORY pragma is used.
**
** @(#) $Id: memjournal.c,v 1.2 2008/10/28 18:12:36 drh Exp $
*/
#include "sqliteInt.h"
/* Forward references to internal structures */
typedef struct MemJournal MemJournal;
typedef struct FilePoint FilePoint;
typedef struct FileChunk FileChunk;
/* Space to hold the rollback journal is allocated in increments of
** this many bytes.
*/
#define JOURNAL_CHUNKSIZE 1024
/* Macro to find the minimum of two numeric values.
*/
#define MIN(x,y) ((x)<(y)?(x):(y))
/*
** The rollback journal is composed of a linked list of these structures.
*/
struct FileChunk {
FileChunk *pNext;
u8 zChunk[JOURNAL_CHUNKSIZE];
FileChunk *pNext; /* Next chunk in the journal */
u8 zChunk[JOURNAL_CHUNKSIZE]; /* Content of this chunk */
};
/*
** An instance of this object serves as a cursor into the rollback journal.
** The cursor can be either for reading or writing.
*/
struct FilePoint {
sqlite3_int64 iOffset;
FileChunk *pChunk;
sqlite3_int64 iOffset; /* Offset from the beginning of the file */
FileChunk *pChunk; /* Specific chunk into which cursor points */
};
/*
** This subclass is a subclass of sqlite3_file. Each open memory-journal
** is an instance of this class.
*/
struct MemJournal {
sqlite3_io_methods *pMethod; /* I/O methods on journal files */
sqlite3_io_methods *pMethod; /* Parent class. MUST BE FIRST */
FileChunk *pFirst; /* Head of in-memory chunk-list */
FilePoint endpoint; /* Pointer to the end of the file */
FilePoint readpoint; /* Pointer to the end of the last xRead() */
@@ -219,5 +238,3 @@ int sqlite3IsMemJournal(sqlite3_file *pJfd){
int sqlite3MemJournalSize(){
return sizeof(MemJournal);
}