Statistics

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

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

        Control stack + Heap: 4000000 bytes
        Control stack in use: 32 bytes
        Heap stack in use:    200 bytes
  
        Program area:         4000000 bytes
        Program area in use:  482984 bytes
  
        Trail stack:          2000000 bytes
        Trail stack in use:   92 bytes
  
        Table area:           2000000 bytes
        Table area in use:    1324 bytes
  
        Number of GC calls:   0
  

• statistics(Key,Value):   The statistics concerning Key are Value. This predicate gives multiple solutions on backtracking. The following shows the output 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?;
        no
  

  The values for all keys are lists of two elements. For runtime, the first element denotes the amount of time in milliseconds elapsed since the start of Prolog and the second element denotes the amount of time elapsed since the previous call to statistics/2 was executed. For the key gc, the number indicates the number of times the garbage collector has been invoked since B-Prolog was started. For all other keys, the first element denotes the size of memory in use and the second element denotes the size of memory 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|_]).