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+/*
+** 2001 September 16
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+**
+******************************************************************************
+**
+** This header file (together with is companion C source-code file
+** "os.c") attempt to abstract the underlying operating system so that
+** the SQLite library will work on both POSIX and windows systems.
+*/
+#ifndef _SQLITE_OS_H_
+#define _SQLITE_OS_H_
+
+/*
+** Figure out if we are dealing with Unix, Windows or MacOS.
+**
+** N.B. MacOS means Mac Classic (or Carbon). Treat Darwin (OS X) as Unix.
+**      The MacOS build is designed to use CodeWarrior (tested with v8)
+*/
+#if !defined(OS_UNIX) && !defined(OS_TEST) && !defined(OS_OTHER)
+# define OS_OTHER 0
+# ifndef OS_WIN
+#   if defined(_WIN32) || defined(WIN32) || defined(__CYGWIN__) || defined(__MINGW32__) || defined(__BORLANDC__)
+#     define OS_WIN 1
+#     define OS_UNIX 0
+#   else
+#     define OS_WIN 0
+#     define OS_UNIX 1
+#  endif
+# else
+#  define OS_UNIX 0
+# endif
+#else
+# ifndef OS_WIN
+#  define OS_WIN 0
+# endif
+#endif
+
+/*
+** Invoke the appropriate operating-system specific header file.
+*/
+#if OS_TEST
+# include "os_test.h"
+#endif
+#if OS_UNIX
+# include "os_unix.h"
+#endif
+#if OS_WIN
+# include "os_win.h"
+#endif
+
+/* os_other.c and os_other.h are not delivered with SQLite.  These files
+** are place-holders that can be filled in by third-party developers to
+** implement backends to their on proprietary operating systems.
+*/
+#if OS_OTHER
+# include "os_other.h"
+#endif
+
+/* If the SET_FULLSYNC macro is not defined above, then make it
+** a no-op
+*/
+#ifndef SET_FULLSYNC
+# define SET_FULLSYNC(x,y)
+#endif
+
+/*
+** Temporary files are named starting with this prefix followed by 16 random
+** alphanumeric characters, and no file extension. They are stored in the
+** OS's standard temporary file directory, and are deleted prior to exit.
+** If sqlite is being embedded in another program, you may wish to change the
+** prefix to reflect your program's name, so that if your program exits
+** prematurely, old temporary files can be easily identified. This can be done
+** using -DTEMP_FILE_PREFIX=myprefix_ on the compiler command line.
+*/
+#ifndef TEMP_FILE_PREFIX
+# define TEMP_FILE_PREFIX "sqlite_"
+#endif
+
+/*
+** The following values may be passed as the second argument to
+** sqlite3OsLock(). The various locks exhibit the following semantics:
+**
+** SHARED:    Any number of processes may hold a SHARED lock simultaneously.
+** RESERVED:  A single process may hold a RESERVED lock on a file at
+**            any time. Other processes may hold and obtain new SHARED locks.
+** PENDING:   A single process may hold a PENDING lock on a file at
+**            any one time. Existing SHARED locks may persist, but no new
+**            SHARED locks may be obtained by other processes.
+** EXCLUSIVE: An EXCLUSIVE lock precludes all other locks.
+**
+** PENDING_LOCK may not be passed directly to sqlite3OsLock(). Instead, a
+** process that requests an EXCLUSIVE lock may actually obtain a PENDING
+** lock. This can be upgraded to an EXCLUSIVE lock by a subsequent call to
+** sqlite3OsLock().
+*/
+#define NO_LOCK         0
+#define SHARED_LOCK     1
+#define RESERVED_LOCK   2
+#define PENDING_LOCK    3
+#define EXCLUSIVE_LOCK  4
+
+/*
+** File Locking Notes:  (Mostly about windows but also some info for Unix)
+**
+** We cannot use LockFileEx() or UnlockFileEx() on Win95/98/ME because
+** those functions are not available.  So we use only LockFile() and
+** UnlockFile().
+**
+** LockFile() prevents not just writing but also reading by other processes.
+** A SHARED_LOCK is obtained by locking a single randomly-chosen 
+** byte out of a specific range of bytes. The lock byte is obtained at 
+** random so two separate readers can probably access the file at the 
+** same time, unless they are unlucky and choose the same lock byte.
+** An EXCLUSIVE_LOCK is obtained by locking all bytes in the range.
+** There can only be one writer.  A RESERVED_LOCK is obtained by locking
+** a single byte of the file that is designated as the reserved lock byte.
+** A PENDING_LOCK is obtained by locking a designated byte different from
+** the RESERVED_LOCK byte.
+**
+** On WinNT/2K/XP systems, LockFileEx() and UnlockFileEx() are available,
+** which means we can use reader/writer locks.  When reader/writer locks
+** are used, the lock is placed on the same range of bytes that is used
+** for probabilistic locking in Win95/98/ME.  Hence, the locking scheme
+** will support two or more Win95 readers or two or more WinNT readers.
+** But a single Win95 reader will lock out all WinNT readers and a single
+** WinNT reader will lock out all other Win95 readers.
+**
+** The following #defines specify the range of bytes used for locking.
+** SHARED_SIZE is the number of bytes available in the pool from which
+** a random byte is selected for a shared lock.  The pool of bytes for
+** shared locks begins at SHARED_FIRST. 
+**
+** These #defines are available in os.h so that Unix can use the same
+** byte ranges for locking.  This leaves open the possiblity of having
+** clients on win95, winNT, and unix all talking to the same shared file
+** and all locking correctly.  To do so would require that samba (or whatever
+** tool is being used for file sharing) implements locks correctly between
+** windows and unix.  I'm guessing that isn't likely to happen, but by
+** using the same locking range we are at least open to the possibility.
+**
+** Locking in windows is manditory.  For this reason, we cannot store
+** actual data in the bytes used for locking.  The pager never allocates
+** the pages involved in locking therefore.  SHARED_SIZE is selected so
+** that all locks will fit on a single page even at the minimum page size.
+** PENDING_BYTE defines the beginning of the locks.  By default PENDING_BYTE
+** is set high so that we don't have to allocate an unused page except
+** for very large databases.  But one should test the page skipping logic 
+** by setting PENDING_BYTE low and running the entire regression suite.
+**
+** Changing the value of PENDING_BYTE results in a subtly incompatible
+** file format.  Depending on how it is changed, you might not notice
+** the incompatibility right away, even running a full regression test.
+** The default location of PENDING_BYTE is the first byte past the
+** 1GB boundary.
+**
+*/
+#define PENDING_BYTE      0x40000000  /* First byte past the 1GB boundary */
+/* #define PENDING_BYTE     0x5400   // Page 22 - for testing */
+#define RESERVED_BYTE     (PENDING_BYTE+1)
+#define SHARED_FIRST      (PENDING_BYTE+2)
+#define SHARED_SIZE       510
+
+
+int sqlite3OsDelete(const char*);
+int sqlite3OsFileExists(const char*);
+int sqlite3OsOpenReadWrite(const char*, OsFile*, int*);
+int sqlite3OsOpenExclusive(const char*, OsFile*, int);
+int sqlite3OsOpenReadOnly(const char*, OsFile*);
+int sqlite3OsOpenDirectory(const char*, OsFile*);
+int sqlite3OsSyncDirectory(const char*);
+int sqlite3OsTempFileName(char*);
+int sqlite3OsIsDirWritable(char*);
+int sqlite3OsClose(OsFile*);
+int sqlite3OsRead(OsFile*, void*, int amt);
+int sqlite3OsWrite(OsFile*, const void*, int amt);
+int sqlite3OsSeek(OsFile*, i64 offset);
+int sqlite3OsSync(OsFile*);
+int sqlite3OsTruncate(OsFile*, i64 size);
+int sqlite3OsFileSize(OsFile*, i64 *pSize);
+char *sqlite3OsFullPathname(const char*);
+int sqlite3OsLock(OsFile*, int);
+int sqlite3OsUnlock(OsFile*, int);
+int sqlite3OsCheckReservedLock(OsFile *id);
+
+
+/* The interface for file I/O is above.  Other miscellaneous functions
+** are below */
+
+int sqlite3OsRandomSeed(char*);
+int sqlite3OsSleep(int ms);
+int sqlite3OsCurrentTime(double*);
+void sqlite3OsEnterMutex(void);
+void sqlite3OsLeaveMutex(void);
+
+#endif /* _SQLITE_OS_H_ */