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Text File | 1990-07-22 | 18KB | 661 lines

                The Icon Memory Monitoring System

                        Gregg M. Townsend
    Department of Computer Science, The University of Arizona



Introduction

   The Icon memory monitoring system (``MemMon'') provides tools
for displaying Icon's allocated data regions [1].  It consists of
instrumentation that produces allocation history files (Appendix
C) and visualization programs that convert allocation history
files to displays that show the sizes, types, and locations of
strings as they are allocated.  The garbage collection process is
shown in detail.

   There are several visualization programs; most of them are
specific to the University of Arizona environment.  Appendix A
describes mmps, a program for producing displays that can be
printed on any PostScript printer.

   An allocation history file is produced by setting the environ-
ment variable MEMMON to the name of the desired file.  No change
in the Icon program is necessary and the production of an alloca-
tion history file does not change program behavior (except for
increasing run time somewhat).  On Unix systems, if the value of
the MEMMON environment variable begins with `|', the rest of the
value is interpreted as a shell command into which the history is
piped.

The_Display

   Icon has two primary allocated data regions: a string region
and a block region.  On implementations that support region
expansion [2], there is also a static region.  The display shows
the regions as if they were contiguous, which they are on imple-
mentations that support region expansion.  The static region, if
it exists, comes first, followed by the string and block regions.
The choice of regions that are displayed can be specified.  By
default, the static region is not displayed, but the string and
block regions are.

   Color distinguishes the various uses of memory, and by infer-
ence the region boundaries.  A legend at the top of the screen
gives the meaning of each color.  Default colors can be changed
by providing an alternate specification file.

   Colors and boundaries are set at allocation time; subsequent
changes are not reflected until garbage collection occurs.  For
example, a string constructed in pieces may not show as a con-
catenated whole.

   The line above the color legend gives the program status at



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the left, the name of the allocation history file in the center,
and storage information at the right, such as

        60480 + 25600 + 51200  (0+0+1+0)

The first three numbers give the current sizes (in bytes) of the
static, string, and block regions respectively.  The ordering
reflects that of the display.  The first three numbers in
parentheses count the garbage collections caused by exhaustion of
the regions, with the fourth number counting garbage collections
initiated by calls to collect(0).

Garbage_Collection

   The garbage collection process is shown in detail by producing
snapshots at critical points.  The first comes at the beginning
of garbage collection, and indicates the reason the garbage col-
lection is required.

   The next snapshot follows the marking phase.  Active data is
dark gray; the remaining blocks are garbage to be discarded.

   The next snapshot shows the marked (active) data in color,
before compaction, with the garbage painted black.  This is the
inverse of the previous display.

   The last snapshot shows the state of memory at the end of gar-
bage collection, after compacting the active data.  All garbage
is gone, and the string region shows a single unbroken string.
At this point the image may be rescaled to handle region expan-
sion.

   Alien blocks (such as I/O buffers) in the static region are
not subject to marking or garbage collection and instead remain
on constant display throughout.  Obsolete co-expression blocks
are freed during the marking phase, but they are displayed in a
manner similar to other blocks so that their disappearance can be
noted.

The_Programmer's_Interface

   Three built-in Icon functions write to the allocation history
to control a subsequent MemMon run.

   mmpause(s) generates a snapshot similar to those during gar-
bage collection; the name comes from its effect on interactive
visualization programs, which pause at this point.  s, if sup-
plied, is displayed to identify the pause.  The default for s is
"programmed pause".

   mmshow(x,s) redraws x if x is in the managed memory region.
This can be used to identify one or more particular data objects
on the display.  s determines the color of x:




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        "w"  white
        "g"  gray
        "b"  black
        "h"  highlight: blinking white and black
        "r"  redraw in normal color (the default)

The altered display persists until the next garbage collection.
If x is outside the managed memory region, no action is taken.

   mmout(s) writes s (without further interpretation) as a
separate line in the history file.  This can be used to insert
comments (beginning with #).

   All three functions return the null value.

Accessing_the_Monitoring_System

   The mmps program is built in the v8/src/memmon subdirectory of
the Icon distribution.  Instructions for running mmps appear in
Appendix B.

   That subdirectory also includes some sample color specifica-
tion files as well as code for building interactive visualization
programs.  Further information about this appears in [3].


References


1.   R. E. Griswold and M. T. Griswold, The Implementation of the
     Icon Programming Language, Princeton University Press, 1986.

2.   R. E. Griswold, Supplementary Information for the
     Implementation of Version 7.9 of Icon, The Univ. of Arizona
     Icon Project Document IPD51d, 1989.

3.   G. M. Townsend, Notes on MemMon Internals, The Univ. of
     Arizona Icon Project Document IPD97a, 1989.

4.   Encapsulated PostScript File Format, Version 1.2, Adobe
     Systems Incorporated, 1987.
















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                      Appendix A:  Running mmps



   mmps generates Encapsulated Postscript [4] displays of Icon
memory.  One or more images are produced under control of command
options.  Output files are Encapsulated PostScript documents
suitable either for direct printing or for incorporation into
other documents.  The output includes full color information,
though most PostScript devices print only the black-and-white
equivalent.

   The default image is 468 x 624 points, or 6.5" x 8.7",
centered on a standard page.  One line represents 1872 bytes of
memory.  Smaller or larger images can be specified; larger ones
are reduced to fit within the above bounds.

Command_format

   mmps  [ options ]  [ file ]

Options

     -r regionsDisplay the indicated memory regions:
             f   static (fixed) region
             s   string region
             b   block region
             The default is -r sb.

     -p when Produce a snapshot at the indicated points:
             f   memory full (beginning of garbage collection)
             g   showing garbage remaining after marking
             a   showing unmarked, active blocks after marking
             c   after compaction (end of garbage collection)
             p   explicit mmpause() calls
             d   (``done'') when the program terminates
             n   never
             The default is -p fgacpd.

     -m      Run through the marking phase even when not pausing
             to display the results.  Normally, marking is
             bypassed if neither of -p ga is selected.

     -g n    Skip to the end of the nth garbage collection before
             displaying anything.

     -q n    Quit after completing the nth garbage collection.

     -Q n    Quit after the nth snapshot.

     -b n    Make each horizontal point represent n bytes of
             memory.  The default is 4.





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     -w n    Set the display width to n points.  The default is
             468.

     -h n    Set the display height to n points.  The default is
             624.

     -L n    Make the legend and status lines n points high.  -L
             0 eliminates the header entirely.  The default is
             11.

     -M n    Limit the memory region lines to a maximum of n
             points in height.  The default is 20.

     -t titleSet the display title.  The default is the
             allocation history file name.

     -c file Use an alternate color specification file (see
             Appendix B).

     -S n    Set the PostScript screen frequency to n lines per
             inch.




































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              Appendix B: Color Specification Files



   A color specification file can be used to change some or all
of the colors produced by mmps.

   The environment variable MMCOLORS can be used to name a file
containing color specifications.  mmps reads this file and uses
it to override the normal defaults.  Then, if a file is passed by
the -c option of mmps, it overrides both the built-in defaults
and anything from an MMCOLORS file.

   Lines in a color specification file contain two whitespace-
separated fields, a label and a value, optionally followed by
comments.  Blank lines are ignored, as are lines beginning with #
.  For example:


        #  change the colors for sets
        set    657  light purple for set headers
        selem  637  medium putple for set elements



   The label field matches either one of the types shown in the
legend or one of these additional keywords:

        background  background
        bsep        block separator
        ssep        string separator
        marked      marked block
        unmarked    unmarked block (when showing active data)
        status      status message
        prompt      prompt message
        title       title field
        regions     region sizes


   The value field is a set of three octal digits specifying a
color.  The digits control the red, green, and blue color
components in that order, with a range of 0 to 7 for each.  A
value of 0 is dark and a value of 7 is light.  For example, 070
is green (0% red + 100% green + 0% blue) and 405 is purple (4/7
red + 5/7 blue).  Unfortunately, the final colors are somewhat
device-dependent because of different responses to the same
specification.










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              Appendix C: Allocation History Files



   An allocation history file is composed of printable characters
forming a sequence of commands that trace interpreter actions
related to memory management.  This section describes the overall
structure of an allocation history file, using terms and commands
that are described later in detail.

   An allocation history file begins with a refresh sequence,
which completely specifies the memory layout at a particular
instant.  The initial refresh sequence gives a snapshot of memory
just before the start of execution.  Within a refresh sequence,
item commands enumerate all the objects within the three regions,
as if they are being placed, in order, into initially empty
regions.

   After the initial refresh sequence, the rest of the file
contains any number of the following components, in any order:
     item commands
     interaction commands
     garbage collection sequences

   Item commands, when outside other sequences, record new
allocations of memory.

   Interaction commands are generated by programmed calls to
mmshow() and mmpause().

   A garbage collection sequence begins with a marking sequence,
in which item commands identify live objects.  The marking
sequence is followed by a new refresh sequence giving the memory
configuration after compaction.  Then, a final marker signals the
end of garbage collection.

   Comment and verification commands may appear at any point in
the file.

Command_Format

   A command has several components:
     [addr+] [len] cmd [etc]

     addr is an optional address, given as a distance from the
          start of a region.  If the address is omitted, the
          current end of the region is assumed.  An address is
          always followed immediately by + .

     len  is a length.  If a length is needed by a command, but
          none is supplied, then the most recent length specified
          for that particular command is used.





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     cmd  is a single character identifying the command.

     etc  is additional information needed by a few particular
          commands.

   Addresses and lengths are nonnegative decimal numbers.  In the
string region, the unit of measurement is a character; in the
static and block regions, it is specified in the refresh sequence
and usually is 4 bytes.

   Whitespace between commands is optional; whitespace within a
command is allowed only in etc data.

Item_Commands

   Item commands identify individual allocated objects.  The
meaning of an item command depends on its context.  Within a
refresh sequence, item commands enumerate the existing
allocations.  Within a marking sequence, item commands mark live
objects.  Otherwise, item commands announce new allocations.

   Except during marking, string and block region item commands
do not include addresses.  Addresses may be obtained by totaling
the allocations made since the beginning of the last refresh
sequence.

   The item commands for the block region are:
     [addr+] [len] c     cset
     [addr+] [len] e     table element trapped variable
     [addr+] [len] E     external block
     [addr+] [len] f     file block
     [addr+] [len] L     list header
     [addr+] [len] l     list element
     [addr+] [len] R     record
     [addr+] [len] r     real number
     [addr+] [len] S     set header
     [addr+] [len] s     set element
     [addr+] [len] T     table header
     [addr+] [len] t     table element
     [addr+] [len] u     substring trapped variable
     [addr+] [len] x     co-expression refresh block

   The string item command is:
     [addr+] [len] "     string

   The static region item commands always include an address.
They are:
     addr + [len] X co-expression block
     addr + [len] A alien block

Refresh_Sequence_Commands
     [units] < static-region_string-region_block-region
            Begin a refresh sequence.  Each region specification
            has the form



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                 base_: used_/ max
            where base is the beginning address of the region,
            used is the amount of memory used, and max is the
            amount of memory allocated to the region.  For the
            static region, the used value is meaningless, and
            base and max are zero with fixed-region versions of
            Icon.  All values in this command are given in bytes.
            The units parameter, if present, gives the size of a
            unit of measurement for other commands referencing
            the static and block regions.  If the units parameter
            is absent, the unit of measurement is four bytes.
     >    End a refresh sequence

Verification_Command
     = static-region_block-region_string-region
            Region specifications are the same as for the <
            command.  This command provides no new information
            but confirms the accumulated memory usage after a
            series of allocations.

Garbage_Collection_Commands
     n_{  Start a garbage collection and begin the marking phase
            n indicates the reason for the collection:
                 0    collect(0) call
                 1    static region
                 2    string region
                 3    block region
     }    End the marking phase
     !    End garbage collection

Interaction_Commands
     ; string
            Pause (produce a snapshot) and display string, which
            includes all characters up to a newline.  This
            command is generated by a programmed mmpause(string)
            call.
     addr_+ len_$ c_t    highlight a string

     addr_+ len_% c_t    highlight a block

     addr_+ len_Y c_t    highlight a static object
            Highlight commands are generated by programmed
            mmshow(x,s) calls.  c is the first character of the
            argument string s, indicating the kind of
            highlighting desired.  t identifies the type of the
            object being highlighted by giving the character used
            for an allocation command of that type.

Comment_Command
     # comment
            All characters following the #, up to a newline, are
            ignored.

Example

   Here is a small, contrived program that builds a list of
strings, then inserts the strings in a set:




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        procedure main ()
           l := list ()
           every put (l, string (-50 to 50))
           s := set ()
           every insert (s, !l)
           end


   Here is the corresponding history file:

        4< 234076:60000/60000 294080:0/65024 359104:0/65024
        2+2666F2670+2050A4722+2A4726+4A4732+8A4742+256A5000+10000X
        0"
        >
        = 234076:60000/60000 294080:0/65024 359104:0/65024
        5L23lLl3"""""""""l""""""""l""""""""31l""""""""""""43l""""2"""""""""1""
        """61l"""""2""""""""""""""""""""""87l"""""""""""""""""""14S10h5sssssss
        sssssssssssssssssssssssssssssssssshsssssssssssssssssssssssssssssssssss
        sssss18hssssssssssssssssssss
        = 234076:60000/60000 294080:233/65024 359104:3524/65024





































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