setMaxThreads
Sets the maximal allowed number of threads for @pool. A value of -1 means that the maximal number of threads is unlimited. If @pool is an exclusive thread pool, setting the maximal number of threads to -1 is not allowed.
Setting @max_threads to 0 means stopping all work for @pool. It is effectively frozen until @max_threads is set to a non-zero value again.
A thread is never terminated while calling @func, as supplied by g_thread_pool_new(). Instead the maximal number of threads only has effect for the allocation of new threads in g_thread_pool_push(). A new thread is allocated, whenever the number of currently running threads in @pool is smaller than the maximal number.
Return
true on success, false if an error occurred
Parameters
a new maximal number of threads for @pool, or -1 for unlimited