Integration with Threads

MzScheme's threads can break external C code under two circumstances:

• Pointers to stack-based values can be communicated between threads. For example, if thread A stores a pointer to a stack-based variable in a global variable, if thread B uses the pointer in the global variable, it may point to data that is not currently on the stack.
• C functions that can invoke MzScheme (and also be invoked by MzScheme) depend on strict function-call nesting. For example, suppose a function F uses an internal stack, pushing items on to the stack on entry and popping the same items on exit. Suppose also that F invokes MzScheme to evaluate an expression. If the evaluate on this expression invoked F again in a new thread, but then returns to the first thread before completeing the second F, then F's internal stack will be corrupted.

If either of these circumstances occurs, MzScheme will probably crash.