Mailfromd
	General-Purpose Mail Filter	Sergey Poznyakoff

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4.1.1 Pragma stacksize

Syntax

#pragma stacksize size
#pragma stacksize size twice|incr
#pragma stacksize size twice|incr max

Description

The stacksize pragma sets the initial size of the run-time stack and may also define the policy of its growing, in case it becomes full. It takes one mandatory and two optional arguments. The first argument gives the desired initial stack size, in words. It defaults to 4096 words. You may wish to increase this number if your configuration program uses recursive functions or does an excessive amount of string manipulations. For example:

#pragma stacksize 7168

The size may end with a usual size suffix, i.e. one of:

File suffixes are case-insensitive:

#pragma stacksize 7m
#pragma stacksize 7M

When the MFL engine notices that there is no more stack space available, it attempts to expand the stack. If this attempt succeeds, the operation continues. Otherwise, a runtime error is reported and the execution of the filter stops.

Optional second argument to #pragma stacksize defines growth policy for the stack. A positive number in its place is taken for the expansion chunk size. In this case, the stack will be grown in blocks that contain integer number of expansion chunks. The following example sets initial stack size to 10240, and expansion chunk size to 2048 words:

#pragma stacksize 10M 2K

This incremental growth policy is the default. The default chunk size is 4096 words.

The word ‘twice’ in the second argument enables exponential stack growth policy:

#pragma stacksize 10240 twice

In this case, when the run-time evaluator hits the stack size limit, it expands the stack to twice the size it had before. So, in the example above, the stack will be sequentially expanded to the following sizes: 20480, 40960, 81920, 163840.

Third argument to #pragma stacksize defines maximum size of the stack. If stack grows beyond this limit, the execution of the script will be aborted.

If you are concerned about the execution time of your script, you may wish to avoid stack reallocations. To help you find out the optimal stack size, each time the stack is expanded, mailfromd issues a warning in its log file, which looks like this:

warning: stack segment expanded, new size=8192

You can use these messages to adjust your stack size configuration settings.

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