SQLite

** structure.  The fcntl() system call is only invoked to set a 
** POSIX lock if the internal lock structure transitions between
** a locked and an unlocked state.
*/

/*
** An instance of the following structure serves as the key used
** to locate a particular lockInfo structure given its inode.  Note
** that we have to include the process ID as part of the key.  On some
** threading implementations (ex: linux), each thread has a separate
** process ID.
*/
struct lockKey {
  dev_t dev;   /* Device number */
  ino_t ino;   /* Inode number */

  pid_t pid;   /* Process ID */

};

/*
** An instance of the following structure is allocated for each inode.
** A single inode can have multiple file descriptors, so each OsFile
** structure contains a pointer to an instance of this object and this
** object keeps a count of the number of OsFiles pointing to it.
*/
struct lockInfo {
  struct lockKey key;  /* The lookup key */
  int cnt;              /* 0: unlocked.  -1: write lock.  1...: read lock. */
  int nRef;             /* Number of pointers to this structure */
};

/* 
** This hash table maps inodes (in the form of lockKey structures) into
** pointers to lockInfo structures.
*/
static Hash lockHash = { SQLITE_HASH_BINARY, 0, 0, 0, 0, 0 };

/*
** Given a file descriptor, locate a lockInfo structure that describes
** that file descriptor.  Create a new one if necessary.  NULL might
** be returned if malloc() fails.
*/
static struct lockInfo *findLockInfo(int fd){
  int rc;
  struct lockKey key;
  struct stat statbuf;
  struct lockInfo *pInfo;
  rc = fstat(fd, &statbuf);
  if( rc!=0 ) return 0;
  memset(&key, 0, sizeof(key));
  key.dev = statbuf.st_dev;
  key.ino = statbuf.st_ino;

  key.pid = getpid();

  pInfo = (struct lockInfo*)sqliteHashFind(&lockHash, &key, sizeof(key));
  if( pInfo==0 ){
    struct lockInfo *pOld;
    pInfo = sqliteMalloc( sizeof(*pInfo) );
    if( pInfo==0 ) return 0;
    pInfo->key = key;
    pInfo->nRef = 1;

# 2003 December 18
#
# 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 file implements regression tests for SQLite library.  The
# focus of this script is multithreading behavior
#
# $Id: thread1.test,v 1.2 2003/12/19 08:40:24 drh Exp $


set testdir [file dirname $argv0]
source $testdir/tester.tcl

# Skip this whole file if the thread testing code is not enabled
#

    INSERT INTO t1 SELECT a+2, b||b FROM t1;
    INSERT INTO t1 SELECT a+4, b||b FROM t1;
    SELECT count(*), max(length(b)) FROM t1;
  }
} {8 64}

# Interleave two threads on read access.  Then make sure a third
# thread can write the database.  In other words:
#
#    read-lock A
#    read-lock B
#    unlock A
#    unlock B
#    write-lock C
#
# At one point, the write-lock of C would fail on Linux. 
#
do_test thread1-1.2 {
  thread_create A test.db
  thread_create B test.db
  thread_create C test.db
  thread_compile A {SELECT a FROM t1}
  thread_step A

  thread_step C
  thread_result C
} SQLITE_DONE
do_test thread1-1.11 {
  thread_finalize C
  thread_result C
} SQLITE_OK
do_test thread1-1.12 {
  catchsql {SELECT name FROM sqlite_master}
  execsql {SELECT name FROM sqlite_master}
} {t1 t2}


# Under this scenario:
#
#    read-lock A
#    read-lock B
#    unlock A
#    write-lock C
#
# Make sure the write-lock fails with SQLITE_BUSY 
#
do_test thread1-2.1 {
  thread_halt *
  thread_create A test.db
  thread_compile A {SELECT a FROM t1}
  thread_step A
  thread_result A
} SQLITE_ROW
do_test thread1-2.2 {
  thread_create B test.db
  thread_compile B {SELECT b FROM t1}
  thread_step B
  thread_result B
} SQLITE_ROW
do_test thread1-2.3 {
  thread_create C test.db
  thread_compile C {INSERT INTO t2 VALUES(98,99)}
  thread_step C
  thread_result C
} SQLITE_BUSY
do_test thread1-2.4 {
  execsql {SELECT * FROM t2}
} {}
do_test thread1-2.5 {
  thread_finalize A
  thread_result A
} SQLITE_OK
do_test thread1-2.6 {
  thread_step C
  thread_result C
} SQLITE_BUSY
do_test thread1-2.7 {
  execsql {SELECT * FROM t2}
} {}
do_test thread1-2.8 {
  thread_finalize B
  thread_result B
} SQLITE_OK
do_test thread1-2.9 {
  thread_step C
  thread_result C
} SQLITE_DONE
do_test thread1-2.10 {
  execsql {SELECT * FROM t2}
} {98 99}
do_test thread1-2.11 {
  thread_finalize C
  thread_result C
} SQLITE_OK

thread_halt *   
finish_test