MapTool Memory Usage

How Maptool Uses Memory

When MapTool starts, the Java virtual machine (the program that lets MapTool run on your computer!) configures a number of settings for the program. Three of these settings affect the memory given to MapTool: heap memory (the memory MapTool uses to store data and resources), and stack memory (the amount of memory threads are allowed to use).

Heap memory

The heap memory allocated to MapTool indicates how much memory MapTool uses to store objects (maps, tokens, image files, macros, etc.) Heap memory allocation is controlled by two options: -Xms sets the starting heap size (the initial amount of memory MapTool is allocated) and -Xmx sets the maximum heap size (the maximum amount of memory MapTool is allowed to access).

If you set the maximum heap size too low, MapTool may run out of memory and crash, freeze, or have other problems. MapTool clients that are connecting to a server should use the same memory settings as the server when possible; otherwise clients may freeze or lose connection when using larger or more complex maps.

Stack memory

The stack memory is the amount of memory each thread is given; threads are sub-processes that handle application functions like network access, macro execution, and drawing the UI. Stack memory allocation is controlled by one option: -Xss sets the stack size (each thread is given exactly the amount specified; there is no starting or maximum stack size).

Some macro frameworks will require larger stack sizes as they perform more complex calculations and functions; they will usually specify their stack requirements. If a thread runs out of stack memory you will see a StackOverflow error and the macro will not work.

Configuring memory allocation for MapTool

In the beginning, MapTool used whatever default stack size and heap size Java felt like setting. The actual amount varied from operating system to operating system, but it was generally enough for the simple macros that were in use at the time. As the power and flexibility of the macro code increased, macros began to bump up against the limits of the default stack, and users began adjusting the stack size to compensate. As frameworks and maps became larger and more complex, users began adjusting the maximum heap size.

The amount of memory is specified in kilobytes or megabytes; "512K" is 512 kilobytes, while "512M" is 512 megabytes.

WARNING: Stack memory is allocated in addition to heap memory and each thread receives the same amount of stack memory. If you set the stack memory allocation too high, the Java VM can consume far more memory than is necessary which will affect overall computer performance.

Setting the memory allocation in a batch file

One of the ways to start MapTool is via the various script or batch files that are included when you download and unzip a copy of MapTool. There are three different types of script files included with MapTool as of 1.3.v77:

Launch MapTool.bat, Launch MapTool-512M-Memory.bat and Launch MapTool-1G-Memory.bat for Windows; the different names refer to different maximum heap allocations
Launch MapTool.sh for Linux and Mac OS X
Launch MapTool.command for Mac OS X; this file can be double-clicked to start MapTool.

Editing a .bat file

Though each batch file has different heap sizes specified, the format is the same:

javaw -Xmx512M -Xss512K -jar maptool-*.jar run

To set the maximum heap size, change the -Xmx option. To set the stack size, change the -Xss option.

Editing the .sh or .command file

At the top of the shell script file are three variables:

MAXMEMSZ="768m"
MINMEMSZ="32m"
STACKSZ="2m"

You can set the starting heap (MINMEMSZ), maximum heap (MAXMEMSZ), and stack size (STACKSZ) by changing these variables.

Setting the memory allocation using MapToolLauncher

If you start MapTool with the Windows launcher, you can set the starting heap (Min Mem), maximum heap (Max Mem), and stack (Stack Size) sizes.

The Windows launcher defaults to a 2MB stack which is perfectly acceptable for pretty much all uses. If you change the memory values, the new values will be saved for the next launch.

Setting the memory allocation for Java WebStart

If you start MapTool using the Java WebStart option, you can change the settings here, too.

Go to the MapTool Launch page
Click the CUSTOMIZATION link; three fields for setting memory options will be exposed
You can set the starting heap (Minimum memory), maximum heap (Maximum memory), and stack size (Stack size) by changing these variables
Click on the links above to start the application you wish to use.

If you have a saved .jnlp (WebStart) file, you can edit the memory settings by hand.

Open the .jnlp file in a text editor
Look for the following section (the actual memory values may differ in your copy):

   <j2se version="1.5+"
       initial-heap-size="64m"
       max-heap-size="512m"
       java-vm-args="-Xmx512m -Xms64m -Xss2m"/>

To change the starting heap size, change the initial-heap-size entry and the -Xms entry
To change the maximum heap size, change the max-heap-size entry and the -Xmx entry
To change the stack memory size, change the -Xss entry
Save the .jnlp file

Setting the memory allocation in the Mac OS X application bundle

Users who download the .dmg (disk image) file from the RPTools web site and installed MapTool from it will see MapTool as a Mac OS X application bundle. MapTool can be launched by double-clicking it like any other Mac OS application.

Ctrl-click (or right-click) on MapTool application icon.
Choose "Show Package Contents" and a new Finder window will open.
Open the Contents folder and locate the Info.plist file.
Ctrl-click (or right-click) on that file and choose Open With > Other...
In the Choose Application dialog that opens, locate TextEdit and double-click on it.
Look for the following section:

   <key>VMOptions</key>
     <array>
       <string>-Xmx768m</string>
       <string>-Xms64m</string>
       <string>-Xss3m</string>
     </array>

To set the starting heap size, change the -Xms option. To set the maximum heap size, change the -Xmx option. To set the stack size, change the -Xss option.
Save the file. The next time you double-click the MapTool icon, it will launch using the new memory settings.