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

On Wednesday, 2 December 2015 at 13:55:02 UTC, Ish wrote:
> 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

You never initialize Mutex, so it is a null pointer when you call `mutex.lock`.

Also, no point in passing a pointer here; just pass `i` instead of `j`.