Hi!
On Tue, 27 Aug 2013 21:30:49 +0000, "Iyer, Balaji V" <balaji.v.i...@intel.com>
wrote:
> --- /dev/null
> +++ gcc/testsuite/c-c++-common/cilk-plus/CK/spawning_arg.c
> @@ -0,0 +1,37 @@
> +/* { dg-do run { target { i?86-*-* x86_64-*-* arm*-*-* } } } */
> +/* { dg-options "-fcilkplus" } */
> +/* { dg-options "-lcilkrts" { target { i?86-*-* x86_64-*-* arm*-*-* } } } */
> +
> +void f0(volatile int *steal_flag)
> +{
> + int i = 0;
> + /* Wait for steal_flag to be set */
> + while (!*steal_flag)
> + ;
> +}
> +
> +int f1()
> +{
> +
> + volatile int steal_flag = 0;
> + _Cilk_spawn f0(&steal_flag);
> + steal_flag = 1; // Indicate stolen
> + _Cilk_sync;
> + return 0;
> +}
> +
> +void f2(int q)
> +{
> + q = 5;
> +}
> +
> +void f3()
> +{
> + _Cilk_spawn f2(f1());
> +}
> +
> +int main()
> +{
> + f3();
> + return 0;
> +}
Is this really well-formed Cilk Plus code? Running with CILK_NWORKERS=1,
or -- the equivalent -- in a system with just one CPU (as per
libcilkrts/runtime/os-unix.c:__cilkrts_hardware_cpu_count returning 1), I
see this test busy-loop as follows:
Breakpoint 1, __cilkrts_hardware_cpu_count () at
../../../source/libcilkrts/runtime/os-unix.c:358
358 {
(gdb) return 1
Make __cilkrts_hardware_cpu_count return now? (y or n) y
#0 cilkg_get_user_settable_values () at
../../../source/libcilkrts/runtime/global_state.cpp:385
385 CILK_ASSERT(hardware_cpu_count > 0);
(gdb) c
Continuing.
^C
Program received signal SIGINT, Interrupt.
f0 (steal_flag=steal_flag@entry=0x7fffffffd03c) at
[...]/source/gcc/testsuite/c-c++-common/cilk-plus/CK/spawning_arg.c:9
9 while (!*steal_flag)
(gdb) info threads
Id Target Id Frame
* 1 Thread 0x7ffff7fcd780 (LWP 30816) "spawning_arg.ex" f0
(steal_flag=steal_flag@entry=0x7fffffffd03c) at
[...]/source/gcc/testsuite/c-c++-common/cilk-plus/CK/spawning_arg.c:9
(gdb) list
4
5 void f0(volatile int *steal_flag)
6 {
7 int i = 0;
8 /* Wait for steal_flag to be set */
9 while (!*steal_flag)
10 ;
11 }
12
13 int f1()
(gdb) bt
#0 f0 (steal_flag=steal_flag@entry=0x7fffffffd03c) at
[...]/source/gcc/testsuite/c-c++-common/cilk-plus/CK/spawning_arg.c:9
#1 0x00000000004009c8 in _cilk_spn_0 () at
[...]/source/gcc/testsuite/c-c++-common/cilk-plus/CK/spawning_arg.c:17
#2 0x0000000000400a4b in f1 () at
[...]/source/gcc/testsuite/c-c++-common/cilk-plus/CK/spawning_arg.c:17
#3 0x0000000000400d0e in _cilk_spn_1 () at
[...]/source/gcc/testsuite/c-c++-common/cilk-plus/CK/spawning_arg.c:30
#4 0x0000000000400d7a in f3 () at
[...]/source/gcc/testsuite/c-c++-common/cilk-plus/CK/spawning_arg.c:30
#5 0x0000000000400e33 in main () at
[...]/source/gcc/testsuite/c-c++-common/cilk-plus/CK/spawning_arg.c:35
No additional thread has been spawned by libcilkrts, and the one initial
thread is stuck in f0, without being able to make progress. Should in
f0's while loop, some function be called to "yield to libcilkrts
scheduler", or should libcilkrts have spawned an additional thread, or is
the test case just not valid Cilk Plus code?
Grüße,
Thomas
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