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POAn "atomic" call to cout in MPI
 

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  1. POAn "atomic" call to cout in MPI
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    <p>I am interested in whether there is a command or a technique within OpenMPI to have an atomic call to write to stdout (or, for that matter, any stream).</p> <p>What I have noticed is that during the execution of MPI programs, calls to write to cout (or other streams) can become confusing, as each proc may write whenever it gets to a certain section of code. When reporting results, a line can be written to by several procs, confusing the issue. So 2 different procs might do something like this:</p> <pre><code>//Proc 10 - results calculated somewhere above // result1 = 10 // result2 = 11 cout &lt;&lt; "My results are: " &lt;&lt; result1 &lt;&lt; " " &lt;&lt; resul2 &lt;&lt; endl; </code></pre> <p>and:</p> <pre><code>//Proc 20 - results calculated somewhere above // result1 = 20 // result2 = 21 cout &lt;&lt; "My results are: " &lt;&lt; result1 &lt;&lt; " " &lt;&lt; resul2 &lt;&lt; endl; </code></pre> <p>But the result might be:</p> <pre><code>My results are: 20 My results are: 10 11 21 </code></pre> <p>What I'm looking for is something like a "blocking" or atomic cout (as well as possibly writing to other streams, such as file streams). So once I start writing a to cout, it blocks until the end of the statement, or until endl or a flush to the stream is issued. If this were the case, I'd be guaranteed that the 2 lines would be separate (but, of course, I still wouldn't know which line would come first):</p> <pre><code>My results are: 20 21 My results are: 10 11 </code></pre>
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    1. USMadeleine P. Vincent
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    1. COTwo different PROCESSES or TWO threads?
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    2. COI was asking about 2 different processes.
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    3. CORunning on the same machine or different machines?
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