STACKSIZE

The executing program maintains a main memory stack for the master thread and distinct stacks for each slave thread. Stacks are temporary memory address spaces used to hold arguments and automatic variables over subprogram invocations.

The default size of the main stack is about eight megabytes. Use the limit command to display the current main stack size as well as set it.

% limit
cputime unlimited
filesize unlimited
datasize 2097148 kbytes
stacksize 8192 kbytes <- current main stack size
coredumpsize 0 kbytes
descriptors 256
memorysize unlimited
% limit stacksize 65536 <- set main stack to 64Mb

Each slave thread of a multithreaded program has its own thread stack. This stack mimics the main stack of the master thread but is unique to the thread. The thread’s private arrays and variables (local to the thread) are allocated on the thread stack.

All slave threads have the same stack size, which is four megabytes for 32-bit applications and eight megabytes for 64-bit applications by default. The size is set with the STACKSIZE environment variable:

% setenv STACKSIZE 16483 <- Set thread stack size to 16 Mb

Setting the thread stack size to a value larger than the default may be necessary for some parallelized code.

Sometimes the compiler may generate a warning message that indicates a bigger stack size is needed. However, it may not be possible to know just how large to set it, except by trial and error, especially if private/local arrays are involved. If the stack size is too small for a thread to run, the program will abort with a segmentation fault.