Statistics

The predicates statistics/0 and statistics/2 are useful for obtaining statistics of the system, such as how much space or time has been consumed, and how much space is left.

• statistics: This predicate displays the number of bytes that are allocated to each data area, and the number of bytes that are already in use. The output looks like:

        Stack+Heap:    12,000,000 bytes
          Stack in use:     1,104 bytes
          Heap in use:        816 bytes
        
        Program:        8,000,000 bytes
          In use:       1,088,080 bytes
        
        Trail:          8,000,000 bytes
          In use:              72 bytes
        
        Table:          4,000,000 bytes
          In use:               0 bytes
        
        Number of GC calls:    0
        Total GC time:         0 ms
        Numbers of expansions: Stack+Heap(0), Program(0), Trail(0), Table(0)
        
        Number of symbols:  5332
        FD backtracks:         0
  

• statistics(Key,Value): The statistics concerning Key are Value. This predicate gives multiple solutions upon backtracking. The following shows the output that the system displays after receiving the query statistics(Key,Value).

        | ?- statistics(Key,Value).
  
        Key = runtime
        Value = [633,633]?;
  
        Key = program
        Value = [483064,3516936]?;
  
        Key = heap
        Value = [364,3999604]?;
  
        Key = control
        Value = [32,3999604]?;
  
        Key = trail
        Value = [108,1999892]?;
  
        Key = table
        Value = [1324,1998676]?;
  
        key = gc
        Value = 0?;
  
        Key = backtracks
        V = 0 ?;
  
        Key = gc_time
        Value = 0 
  
        no
  

  For all keys, the values are lists of two elements. For runtime, the first element denotes the amount of time that has elapsed since the start of Prolog, in milliseconds, and the second element denotes the amount of time that has elapsed since the previous call to statistics/2 was executed. For the key gc, the number indicates the number of times that the garbage collector has been invoked. For the key backtracks, the number indicates the number of backtracks done in the labeling of finite domain variables since B-Prolog was started. For all other keys, the first element denotes the size of the memory that is in use, and the second element denotes the size of the memory that is still available in the corresponding data area.
• cputime(T): The current cpu time is T. It is implemented as follows:

        cputime(T):-statistics(runtime,[T|_]).
  

• time(Goal): Calls Goal, and reports the CPU time that is consumed by the execution. It is defined as follows:

        time(Goal):-
            cputime(Start),
            call(Goal),
            cputime(End),
            T is (End-Start)/1000,
            format(``CPU time ~w seconds. ``, [T]).