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198 lines
7.5 KiB
C
198 lines
7.5 KiB
C
/*
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** 2001 September 16
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**
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** The author disclaims copyright to this source code. In place of
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** a legal notice, here is a blessing:
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**
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** May you do good and not evil.
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** May you find forgiveness for yourself and forgive others.
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** May you share freely, never taking more than you give.
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**
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******************************************************************************
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**
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** This header file (together with is companion C source-code file
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** "os.c") attempt to abstract the underlying operating system so that
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** the SQLite library will work on both POSIX and windows systems.
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*/
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#ifndef _SQLITE_OS_H_
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#define _SQLITE_OS_H_
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/*
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** Figure out if we are dealing with Unix, Windows or MacOS.
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**
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** N.B. MacOS means Mac Classic (or Carbon). Treat Darwin (OS X) as Unix.
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** The MacOS build is designed to use CodeWarrior (tested with v8)
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*/
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#if !defined(OS_UNIX) && !defined(OS_TEST)
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# ifndef OS_WIN
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# ifndef OS_MAC
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# if defined(__MACOS__)
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# define OS_MAC 1
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# define OS_WIN 0
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# define OS_UNIX 0
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# elif defined(_WIN32) || defined(WIN32) || defined(__CYGWIN__) || defined(__MINGW32__) || defined(__BORLANDC__)
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# define OS_MAC 0
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# define OS_WIN 1
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# define OS_UNIX 0
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# else
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# define OS_MAC 0
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# define OS_WIN 0
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# define OS_UNIX 1
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# endif
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# else
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# define OS_WIN 0
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# define OS_UNIX 0
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# endif
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# else
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# define OS_MAC 0
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# define OS_UNIX 0
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# endif
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#else
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# define OS_MAC 0
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# ifndef OS_WIN
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# define OS_WIN 0
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# endif
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#endif
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/*
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** Invoke the appropriate operating-system specific header file.
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*/
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#if OS_TEST
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# include "os_test.h"
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#endif
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#if OS_UNIX
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# include "os_unix.h"
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#endif
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#if OS_WIN
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# include "os_win.h"
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#endif
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#if OS_MAC
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# include "os_mac.h"
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#endif
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/*
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** Temporary files are named starting with this prefix followed by 16 random
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** alphanumeric characters, and no file extension. They are stored in the
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** OS's standard temporary file directory, and are deleted prior to exit.
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** If sqlite is being embedded in another program, you may wish to change the
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** prefix to reflect your program's name, so that if your program exits
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** prematurely, old temporary files can be easily identified. This can be done
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** using -DTEMP_FILE_PREFIX=myprefix_ on the compiler command line.
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*/
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#ifndef TEMP_FILE_PREFIX
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# define TEMP_FILE_PREFIX "sqlite_"
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#endif
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/*
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** The following values may be passed as the second argument to
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** sqlite3OsLock(). The various locks exhibit the following semantics:
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**
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** SHARED: Any number of processes may hold a SHARED lock simultaneously.
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** RESERVED: A single process may hold a RESERVED lock on a file at
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** any time. Other processes may hold and obtain new SHARED locks.
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** PENDING: A single process may hold a PENDING lock on a file at
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** any one time. Existing SHARED locks may persist, but no new
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** SHARED locks may be obtained by other processes.
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** EXCLUSIVE: An EXCLUSIVE lock precludes all other locks.
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**
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** PENDING_LOCK may not be passed directly to sqlite3OsLock(). Instead, a
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** process that requests an EXCLUSIVE lock may actually obtain a PENDING
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** lock. This can be upgraded to an EXCLUSIVE lock by a subsequent call to
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** sqlite3OsLock().
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*/
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#define NO_LOCK 0
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#define SHARED_LOCK 1
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#define RESERVED_LOCK 2
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#define PENDING_LOCK 3
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#define EXCLUSIVE_LOCK 4
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/*
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** File Locking Notes: (Mostly about windows but also some info for Unix)
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**
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** We cannot use LockFileEx() or UnlockFileEx() on Win95/98/ME because
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** those functions are not available. So we use only LockFile() and
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** UnlockFile().
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**
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** LockFile() prevents not just writing but also reading by other processes.
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** A SHARED_LOCK is obtained by locking a single randomly-chosen
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** byte out of a specific range of bytes. The lock byte is obtained at
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** random so two separate readers can probably access the file at the
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** same time, unless they are unlucky and choose the same lock byte.
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** An EXCLUSIVE_LOCK is obtained by locking all bytes in the range.
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** There can only be one writer. A RESERVED_LOCK is obtained by locking
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** a single byte of the file that is designated as the reserved lock byte.
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** A PENDING_LOCK is obtained by locking a designated byte different from
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** the RESERVED_LOCK byte.
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**
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** On WinNT/2K/XP systems, LockFileEx() and UnlockFileEx() are available,
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** which means we can use reader/writer locks. When reader/writer locks
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** are used, the lock is placed on the same range of bytes that is used
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** for probabilistic locking in Win95/98/ME. Hence, the locking scheme
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** will support two or more Win95 readers or two or more WinNT readers.
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** But a single Win95 reader will lock out all WinNT readers and a single
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** WinNT reader will lock out all other Win95 readers.
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**
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** The following #defines specify the range of bytes used for locking.
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** SHARED_SIZE is the number of bytes available in the pool from which
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** a random byte is selected for a shared lock. The pool of bytes for
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** shared locks begins at SHARED_FIRST.
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**
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** These #defines are available in os.h so that Unix can use the same
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** byte ranges for locking. This leaves open the possiblity of having
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** clients on win95, winNT, and unix all talking to the same shared file
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** and all locking correctly. To do so would require that samba (or whatever
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** tool is being used for file sharing) implements locks correctly between
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** windows and unix. I'm guessing that isn't likely to happen, but by
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** using the same locking range we are at least open to the possibility.
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**
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** Locking in windows is manditory. For this reason, we cannot store
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** actual data in the bytes used for locking. The pager never allocates
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** the pages involved in locking therefore. SHARED_SIZE is selected so
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** that all locks will fit on a single page even at the minimum page size.
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** PENDING_BYTE defines the beginning of the locks. By default PENDING_BYTE
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** is set high so that we don't have to allocate an unused page except
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** for very large databases. But one should test the page skipping logic
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** by setting PENDING_BYTE low and running the entire regression suite.
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**
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** Changing the value of PENDING_BYTE results in a subtly incompatible
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** file format. Depending on how it is changed, you might not notice
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** the incompatibility right away, even running a full regression test.
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** The default location of PENDING_BYTE is the first byte past the
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** 1GB boundary.
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**
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*/
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#define PENDING_BYTE 0x40000000 /* First byte past the 1GB boundary */
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/* #define PENDING_BYTE 0x5400 // Page 20 - for testing */
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#define RESERVED_BYTE (PENDING_BYTE+1)
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#define SHARED_FIRST (PENDING_BYTE+2)
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#define SHARED_SIZE 510
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int sqlite3OsDelete(const char*);
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int sqlite3OsFileExists(const char*);
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int sqlite3OsOpenReadWrite(const char*, OsFile*, int*);
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int sqlite3OsOpenExclusive(const char*, OsFile*, int);
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int sqlite3OsOpenReadOnly(const char*, OsFile*);
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int sqlite3OsOpenDirectory(const char*, OsFile*);
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int sqlite3OsSyncDirectory(const char*);
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int sqlite3OsTempFileName(char*);
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int sqlite3OsClose(OsFile*);
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int sqlite3OsRead(OsFile*, void*, int amt);
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int sqlite3OsWrite(OsFile*, const void*, int amt);
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int sqlite3OsSeek(OsFile*, i64 offset);
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int sqlite3OsSync(OsFile*);
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int sqlite3OsTruncate(OsFile*, i64 size);
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int sqlite3OsFileSize(OsFile*, i64 *pSize);
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int sqlite3OsRandomSeed(char*);
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int sqlite3OsSleep(int ms);
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int sqlite3OsCurrentTime(double*);
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int sqlite3OsFileModTime(OsFile*, double*);
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void sqlite3OsEnterMutex(void);
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void sqlite3OsLeaveMutex(void);
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char *sqlite3OsFullPathname(const char*);
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int sqlite3OsLock(OsFile*, int);
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int sqlite3OsUnlock(OsFile*, int);
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int sqlite3OsCheckReservedLock(OsFile *id);
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#endif /* _SQLITE_OS_H_ */
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