SQLite

proc do_thread_test2 {args} {
  set name [lindex $args 0]
  if {[lsearch $args -processes]>=0} { error "bad option: -processes"}
  uplevel [lreplace $args 0 0 do_thread_test "$name-threads" -processes 0]
  uplevel [lreplace $args 0 0 do_thread_test "$name-processes" -processes 1]
}


#--------------------------------------------------------------------------
# Start 10 threads. Each thread performs both read and write 
# transactions. Each read transaction consists of:
#
#   1) Reading the md5sum of all but the last table row,
#   2) Running integrity check.
#   3) Reading the value stored in the last table row,

  execsql {
    PRAGMA journal_mode = WAL;
    CREATE TABLE t1(a INTEGER PRIMARY KEY, b UNIQUE);
  }
} -thread r 1 {
  # This connection only ever reads the database. Therefore the 
  # busy-handler is not required. Disable it to check that this is true.

  #
  # UPDATE: That is no longer entirely true - as we don't use a blocking
  # lock to enter RECOVER state. Which means there is a small chance a
  # reader can see an SQLITE_BUSY.
  #
  while {[tt_continue]} {
    integrity_check
  }
  set {} ok
} -thread w 1 {

  proc wal_hook {zDb nEntry} {
    if {$nEntry>15} {db eval {PRAGMA wal_checkpoint}}
    return 0
  }