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@(@\newcommand{\W}[1]{ \; #1 \; } \newcommand{\R}[1]{ {\rm #1} } \newcommand{\B}[1]{ {\bf #1} } \newcommand{\D}[2]{ \frac{\partial #1}{\partial #2} } \newcommand{\DD}[3]{ \frac{\partial^2 #1}{\partial #2 \partial #3} } \newcommand{\Dpow}[2]{ \frac{\partial^{#1}}{\partial {#2}^{#1}} } \newcommand{\dpow}[2]{ \frac{ {\rm d}^{#1}}{{\rm d}\, {#2}^{#1}} }@)@
Multi-Threaded Implementation of Summation of 1/i

Syntax
ok = harmonic_sum(sum, num_sum)

Purpose
Multi-threaded computation of the summation that defines the harmonic series @[@ s = 1 + 1/2 + 1/3 + ... + 1/n @]@

Thread
It is assumed that this function is called by thread zero, and all the other threads are blocked (waiting).

ok
This return value has prototype
     bool ok
 If this return value is false, an error occurred during harmonic.

sum
This argument has prototype
     double& sum
 The input value of the argument does not matter. Upon return it is the value of the summation; i.e. @(@ s @)@.

num_sum
This argument has prototype
     size_t num_sum
 It specifies the number of terms in the summation; i.e. @(@ n @)@.

Source 

namespace {
bool harmonic_sum(double& sum, size_t num_sum)
{     // sum = 1/num_sum + 1/(num_sum-1) + ... + 1
     bool ok = true;
     ok     &= thread_alloc::thread_num() == 0;

     // setup the work for multi-threading
     ok &= harmonic_setup(num_sum);

     // now do the work for each thread
     if( num_threads_ > 0 )
          team_work( harmonic_worker );
     else     harmonic_worker();

     // combine the result for each thread and takedown the multi-threading.
     ok &= harmonic_takedown(sum);

     return ok;
}
}
Input File: example/multi_thread/harmonic.cpp