MemMon -- A Case History

• MemMon ("Memory Monitor") was developed to visualize storage management in Icon
  
• it is a classic example of adding instrumentation to an implementation
  
• the instrumentation writes event information to a file
  
• instrumentation is enabled by defining an environment variable (MEMMON) that specified the file for monitoring output
  
• the output usually is processed in flight-recorder mode after program execution, but MEMMON can be defined to be a pipe, so that storage management can be visualized while the program being monitor is running
  
• since the instrumentation applies only to storage management - allocation and garbage collection -- it is confined to a few modules
  
• macros are used to produce monitoring output, so that Icon can be built with or without memory monitoring enabled; the macros simply are defined to be empty if Icon is built
  
• MemMon instrumentation has been replaced by more comprehensive instrumentation in the current version of Icon, but MemMon still is available in an older version

MemMon Instrumentation

• when storage is allocated, the event produced gives its type and size (if it is not determined by the type)
  
• typical calls of instrumentation code look like this:

               ...

      StrLen(ts) = slen;
      StrLoc(ts) = s;
      if (!collect(Strings, slen))
         return NULL;
      s = StrLoc(ts);
      }
   MMStr(slen);                    /* string allocation */
   strtotal += slen;
               ...

      struct region *rp = NULL;
      if (DiffPtrs(blkend, blkfree) < nbytes) {
      if (!collect(Blocks, nbytes))
          return NULL;
      }
   MMAlc((word)nbytes, t_code);    /* block allocation */
            ...

  if (InRange(blkbase, block, blkfree)) {
      type = BlkType(block);
      if ((uword)type <= MaxType) {
         endblock = block + BlkSize(block);
         MMMark(block, (int)type);  /* block marked */
         }

MemMon Output

• MemMon output is ASCII text, but formatted for "easy" viewing instead of being a simple event stream:

##  Icon MemMon output
#
#   program: ./rsg
#   date:    Fri May 18 09:35:34 1990

4< 155484:68160/68160 223680:0/46080 269760:0/92160
2+4524F4528+2048A6578+256A6836+202A7040+10000X
0"
>
= 155484:68160/68160 223680:0/46080 269760:0/92160
5L23lL21l16T10h7eL9lLl80+7%rteLlLl115+%rteLlLl150+%rteLlLl185+%rteLlLl
220+%rte6RLlLl255+%rteRLlLl296+%rteRLlLl337+%rtLl2478+2048A41"5ueL23l10c
LlcRccRccRccRccc397+%rt35"ueLlcLlcRccRccRccc599+%rt32"ueLlcLlcRccRccRc
cc775+%rt148"ueLlcLlccc951+%rt46"ueLlcLlcRcRcRcRcRcRcRcc1059+%rt50"ueL
lcLlcccLlcccLlcccLlcccLlccc1269+%rt56"ueLlcLlcccLlcccLlcccLlcccLlccc1609+%rt
84"ueLlcLlcccLlcccLlcccLlcccLlcccLlcccLlcccLlcccLlcclc1949+%rt64"ueLlc
LlccRccLlccRccLlccRccLlccRccRcc2544+%rt62"ueLlcLlcccLlcccLlcccLlcccLlc
ccLlccc2916+%rt34"ueLlcLlcccLlcccLlccc3314+%rt28"ueLlcLlcRccRcc3538+%rt
17"ueLlcLlcccLlccc3678+%rt54"ueLlcLlcccLlcccLlcccLlcccLlcccLlcccLlcccL
lccc3844+%rt37"ueLlcLlcccLlcccLlcccLlccc4358+%rt8"uRL9lL21lL7lL9lL19l0"
138"L9lL17l1"L19lL15lL9lL25l18"1"L9lL21l8"2"L11lL17l4"L9lL17l7"1"L9lL13l
"L19lL11lL9lL21l5"1"L9lL17l3"1"L9lL13l9"1"L9lLl"LlL7l"428+ARL9lL21lL7l
L9lL19l0"138"L9lL17l1"L19lL15lL9lL25l3"1"L9lL21l7"2"L15lL17l6"L9lL21l9"
1"L9lL17l6"1"L9lL13l"L19lL11lL9lL21l11"1"L9lL17l18"1"L9lL13l6"1"L9lLl"
LlL7l"RL9lL21lL7lL9lL19l0"138"L9lL17l1"L19lL15lL9lL25l7"1"L9lL21l9"2"L
11lL17l4"L9lL17l6"1"L9lL13l"L19lL11lL9lL21l11"1"L9lL17l7"1"L9lL13l6"1"
L9lLl"LlL7l"RL9lL21lL7lL9lL19l0"138"L9lL17l1"L19lL15lL9lL25l18"1"L9lL21l
6"2"L15lL17l6"L9lL21l9"1"L9lL17l11"1"L9lL13l"L19lL11lL9lL21l7"1"L9lL17l

MemMon Visualization

• MemMon output would be easier to handle if it were written as a simple event stream
  
• the output of the MemMon instrumentation can be used in many ways
  
• the primary use of MemMon output has been to provide animated visualizations of storage management
  
• the visualization shows the string and block regions in proportion to their actual sizes as folded strips of cells
  
• types are coded by colors; different palettes are available
  
• when storage is allocated, it is shown at the position it is allocated and with its size in proportion
  
• in the string region, the last pixel of each allocation is highlighted so that the sizes of allocated strings can be determined

MemMon Visualization Layout

MemMon Visualization Example

just prior to garbage collection:



data to be saved highlighted:



data to be discarded highlighted:



saved data compacted:

Using MemMon to Compare Programming Techniques

Concordance Program Using Strings:

global uses, lineno, width

procedure main(args)
   local word, line

   width := 15	# width of word field
   uses := table("")
   lineno := 0
   every tabulate(words())	# tabulate all the citations
   output()	# print the citations
end
          ...

procedure tabulate(word)
   if uses[word][-2 -:*lineno] == lineno then return
   else {
   uses[word] ||:= lineno || ", "	# new line number
   return
   }
end

procedure output()
   local word

   write()
   uses := sort(uses,3)	# sort citations
   while word := get(uses) do
      write(left(word, width), get(uses)[1:-2])
end

Concordance Program Using Lists:

          ...

procedure tabulate(word)
   if /uses[word] := [lineno] then return
   else {
   if uses[word][-1] ~= lineno then put(uses[word] ,lineno)
   return
   }
end
          ...

procedure output()
   local word, line, numbers

   write()
   uses := sort(uses,3) # sort citations
   while word := get(uses) do {
      line := ""
      numbers := get(uses)
      while line ||:= get(numbers) || ", "
      write(left(word, width), line[1:-2])
      }
end

Concordance Program Using Sets:

procedure tabulate(word)
   /uses[word] := set()
   insert(uses[word], lineno)
   return
end
          ...

procedure output()
   local word, line, numbers

   write()
   uses := sort(uses,3)
   while word := get(uses) do {
      line := ""
      numbers := sort(get(uses))
      while line ||:= get(numbers) || ", "
      write(left(word, width), line[1:-2])
      }
end

Concordance Program Using Tables:

procedure tabulate(word)
   /uses[word] := table()
   uses[word][lineno] := 1
   return
end
          ...

procedure output()
   local word, line, numbers

   write()
   uses := sort(uses,3)
   while word := get(uses) do {
   line := ""
   numbers := sort(get(uses),3)
   while line ||:= get(numbers) || ", " do
      get(numbers)
      write(left(word,width), line[1:-2])
      }
end

Different MemMon Palettes