mutex usage problem?

[Ish via Digitalmars-d-learn]

The following code does core dump (compiled with gdc). Pointers 
will be appreciated.
import std.stdio;
import std.conv;
import std.math;
import std.concurrency;
import core.thread;
import core.sync.mutex;

enum count = 5;
__gshared double rslt = 0.0;
__gshared Mutex mutex;

void term(immutable(int)* nterm) {
	double r;
	auto n = to!double(*nterm);
	r = 4.0*pow(-1.0, *nterm)/(2.0*n + 1);
	writefln("%s: %6.6f.", *nterm, r);
	mutex.lock();
	   rslt = rslt + r;
	mutex.unlock();
}


void main() {

     foreach (i; 0 .. count) {
	int* jm = new int;
         *jm = i;
	immutable int *j = cast(immutable) jm;
         Tid tid = spawn(&term, j);
     }

     thread_joinAll();
     writefln("Result: %6.9f.", rslt);
}

-ish