2.3.1 Data Races in omp_prime.c

% cc -xopenmp=noopt omp_prime.c -lm -xinstrument=datarace

% collect -r race a.out | sort -n 
0
0
0
0
0
0
0
0
0
0
...
0
0
Creating experiment database test.1.er ...
Number of prime numbers between 2 and 3000: 429
2
3
5
7
11
13
17
19
23
29
31
37
41
47
53
59
61
67
71
73
...
2971
2999

% er_print test.1.er 
(er_print) races

Total Races:  4 Experiment:  test.1.er

Race #1, Vaddr: 0xffbfeec4
      Access 1: Read,  main -- MP doall from line 42 [_$d1A42.main] + 0x00000060,
                       line 45 in "omp_prime.c"
      Access 2: Write, main -- MP doall from line 42 [_$d1A42.main] + 0x0000008C,
                       line 46 in "omp_prime.c"
  Total Traces: 2

Race #2, Vaddr: 0xffbfeec4
      Access 1: Write, main -- MP doall from line 42 [_$d1A42.main] + 0x0000008C,
                       line 46 in "omp_prime.c"
      Access 2: Write, main -- MP doall from line 42 [_$d1A42.main] + 0x0000008C,
                       line 46 in "omp_prime.c"
  Total Traces: 1

Race #3, Vaddr: (Multiple Addresses)
      Access 1: Write, main -- MP doall from line 42 [_$d1A42.main] + 0x0000007C,
                       line 45 in "omp_prime.c"
      Access 2: Write, main -- MP doall from line 42 [_$d1A42.main] + 0x0000007C,
                       line 45 in "omp_prime.c"
  Total Traces: 1

Race #4, Vaddr: 0x21418
      Access 1: Read,  is_prime + 0x00000074,
                       line 18 in "omp_prime.c"
      Access 2: Write, is_prime + 0x00000114,
                       line 21 in "omp_prime.c"
  Total Traces: 1
(er_print)

The following screen-shot shows the races that were detected in omp_primes.c as displayed by the Thread Analyzer GUI. The command to invoke the GUI and load the experiment data is tha test.1.er.

Figure 2–1 Data Races Detected in omp_primes.c

There are four data-races in omp_primes.c:

• Race number one: A data-race between a read from total on line 45 and a write to total on line 46.

• Race number two: A data-race between a write to total on line 46 and another write to total on the same line.

• Race number three: A data-race between a write to primes[] on line 45 and another write to primes[] on the same line.

• Race number four: A data-race between a read from pflag[] on line 18 and a write to pflag[] on line 21.