SQLite

    proc checkpoint {db mode args} {
      eval sqlite3_wal_checkpoint_v2 [list $db] [list $mode] $args
    }
  }

  2 {
    proc checkpoint {db mode args} {
      set sql "PRAGMA wal_checkpoint = $mode"
      if {[llength $args] && [lindex $args 0]!=""} {
        set sql "PRAGMA [lindex $args 0].wal_checkpoint = $mode"
      }
      set rc [catch { $db eval $sql } msg]
      if {$rc} {
        regsub {database} $msg {database:} msg
        error "[sqlite3_errcode $db] - $msg"
      }
      set msg

    set ::write_errors
  } {}

  db close
  db2 close
  tvfs delete

  proc busy_handler {mode busy_handler_mode n} {
    incr ::busy_handler_counter
    switch -- $busy_handler_mode {
      1 {
        # Do nothing. Do not block.
        return 1
      }

      2 {
        # Close first the reader, then later the writer.
        if {$n==5}  { catch {db2 eval commit} }
        if {$n==10} { catch {db3 eval commit} }
        return 0
      }

      3 {
        # Close first the writer, then later the reader.
        if {$n==5}  { catch {db2 eval commit} }
        if {$n==10} { catch {db3 eval commit} }
        return 0
      }
    }
  }

  foreach {mode busy_handler_mode} { 
    passive 1
    full    1
    full    2
    full    3
  } {

    set ::sync_counter 0

    proc tvfs_callback {method args} {
      set tail [file tail [lindex $args 0]]
      if {$method == "xSync" && $tail == "test.db"} {
        incr ::sync_counter
      }

      if {$method == "xWrite" && $tail=="test.db"} {
        if {$::write_ok < 0} {
          set ::write_ok [expr ![catch {db5 eval { BEGIN IMMEDIATE }}]]
          catch { db5 eval ROLLBACK }
        }
        if {$::read_ok < 0} {
          set ::read_ok [expr ![catch {db5 eval { SELECT * FROM t1 }}]]
        }
      }
    }

    catch { db close }
    forcedelete test.db
    testvfs tvfs
    sqlite3 db test.db -vfs tvfs
    #tvfs filter xSync
    tvfs script tvfs_callback

    do_execsql_test $tn.4.$mode.0 {
      CREATE TABLE t1(a, b);
      CREATE TABLE t2(a, b);
      PRAGMA journal_mode = wal;
      INSERT INTO t1 VALUES(1, 2);
      INSERT INTO t1 VALUES(3, 4);
      INSERT INTO t1 VALUES(5, 6);
    } {wal}

    # Open a reader on the current database snapshot.
    do_test $tn.4.$mode.1 {
      sqlite3 db2 test.db -vfs tvfs
      execsql {
        BEGIN;
          SELECT * FROM t1 UNION ALL SELECT * FROM t2;
      } db2
    } {1 2 3 4 5 6}

    # Open a writer. Write a transaction. Then begin, but do not commit,
    # a second transaction.
    do_test $tn.4.$mode.2 {
      sqlite3 db3 test.db -vfs tvfs
      execsql {
        INSERT INTO t2 VALUES(7, 8);
        BEGIN;
          INSERT INTO t2 VALUES(9, 10);
          SELECT * FROM t1 UNION ALL SELECT * FROM t2;
      } db3
    } {1 2 3 4 5 6 7 8 9 10}

    sqlite3 db5 test.db -vfs tvfs

    # Register a busy-handler with connection [db].
    #
    db busy [list busy_handler $mode $busy_handler_mode]
    set ::sync_counter 0
    set ::busy_handler_counter 0
    set ::read_ok -1
    set ::write_ok -1
    
    do_test $tn.4.$mode.3 {
      checkpoint db $mode main
      set {} {}
    } {}

    if { $mode=="passive" } {
      # EVIDENCE-OF: R-16333-64433 Checkpoint as many frames as possible
      # without waiting for any database readers or writers to finish, then
      # sync the database file if all frames in the log were checkpointed.
      #
      #   "As many frames as possible" means all but the last two transactions
      #   (the two that write to table t2, of which the scond is unfinished).
      #   So copying the db file only we see the t1 change, but not the t2
      #   modifications.
      #
      #   The busy handler is not invoked (see below) and the db reader and
      #   writer are still active - so the checkpointer did not wait for either
      #   readers or writers. As a result the checkpoint was not finished and
      #   so the db file is not synced.
      #
      # EVIDENCE-OF: R-62920-47450 The busy-handler callback is never invoked
      # in the SQLITE_CHECKPOINT_PASSIVE mode.
      #
      #   It's not. Test case "$tn.4.$mode.6".
      #
      do_test $tn.4.$mode.4 {
        forcecopy test.db abc.db
        sqlite3 db4 abc.db
        db4 eval { SELECT * FROM t1 UNION ALL SELECT * FROM t2 }
      } {1 2 3 4 5 6}
      do_test $tn.4.$mode.5 { set ::sync_counter } 0
      do_test $tn.4.$mode.6 { set ::busy_handler_counter } 0
      db4 close
  
      db2 eval COMMIT
      db3 eval COMMIT
  
      # EVIDENCE-OF: R-65499-53765 On the other hand, passive mode might leave
      # the checkpoint unfinished if there are concurrent readers or writers.
      #
      #   The reader and writer have now dropped their locks. And so a 
      #   checkpoint now is able to checkpoint more frames. Showing that the
      #   attempt above was left "unfinished".
      #
      #   Also, because the checkpoint finishes this time, the db is synced.
      #   Which is part of R-16333-64433 above.
      #
      do_test $tn.4.$mode.7 {
        checkpoint db $mode main
        forcecopy test.db abc.db
        sqlite3 db4 abc.db
        db4 eval { SELECT * FROM t1 UNION ALL SELECT * FROM t2 }
      } {1 2 3 4 5 6 7 8 9 10}
      do_test $tn.4.$mode.6 { set ::sync_counter } 1
      do_test $tn.4.$mode.7 { set ::busy_handler_counter } 0
      db4 close
    }

    if { $mode=="full" } {
      if {$busy_handler_mode==2 || $busy_handler_mode==3} {
        # EVIDENCE-OF: R-59171-47567 This mode blocks (it invokes the
        # busy-handler callback) until there is no database writer and all
        # readers are reading from the most recent database snapshot.
        #
        #   Show that both the reader and writer have finished:
        #
        do_test $tn.4.$mode.7 {
          list [catchsql COMMIT db2] [catchsql COMMIT db3]
        } [list                                             \
            {1 {cannot commit - no transaction is active}}  \
            {1 {cannot commit - no transaction is active}}  \
        ]

        # EVIDENCE-OF: R-29177-48281 It then checkpoints all frames in the log
        # file and syncs the database file.
        #
        do_test $tn.4.$mode.8 {
          forcecopy test.db abc.db
          sqlite3 db4 abc.db
          db4 eval { SELECT * FROM t1 UNION ALL SELECT * FROM t2 }
        } {1 2 3 4 5 6 7 8 9 10}
        do_test $tn.4.$mode.9 { set ::sync_counter } 1
        db4 close

        # EVIDENCE-OF: R-51867-44713 This mode blocks new database writers
        # while it is pending, but new database readers are allowed to continue
        # unimpeded.
        do_test $tn.4.$mode.10 {
          list $::write_ok $::read_ok
        } {0 1}

      }
    }

    db2 close
    db3 close
    db5 close
  }

  db close
  tvfs delete
}

#-----------------------------------------------------------------------
# EVIDENCE-OF: R-03996-12088 The M parameter must be a valid checkpoint
# mode:
#
#   Valid checkpoint modes are 0, 1, 2 and 3.