diff options
Diffstat (limited to 'cpukit/score/cpu/no_cpu/rtems/score/cpu.h')
| -rw-r--r-- | cpukit/score/cpu/no_cpu/rtems/score/cpu.h | 33 |
1 files changed, 31 insertions, 2 deletions
diff --git a/cpukit/score/cpu/no_cpu/rtems/score/cpu.h b/cpukit/score/cpu/no_cpu/rtems/score/cpu.h index 9570fb6c8d..0fcc6e719c 100644 --- a/cpukit/score/cpu/no_cpu/rtems/score/cpu.h +++ b/cpukit/score/cpu/no_cpu/rtems/score/cpu.h @@ -578,11 +578,40 @@ typedef struct { #ifdef RTEMS_SMP /** * @brief On SMP configurations the thread context must contain a boolean - * indicator if this context is executing on a processor. + * indicator to signal if this context is executing on a processor. * * This field must be updated during a context switch. The context switch * to the heir must wait until the heir context indicates that it is no - * longer executing on a processor. + * longer executing on a processor. The context switch must also check if + * a thread dispatch is necessary to honor updates of the heir thread for + * this processor. This indicator must be updated using an atomic test and + * set operation to ensure that at most one processor uses the heir + * context at the same time. + * + * @code + * void _CPU_Context_switch( + * Context_Control *executing, + * Context_Control *heir + * ) + * { + * save( executing ); + * + * executing->is_executing = false; + * memory_barrier(); + * + * if ( test_and_set( &heir->is_executing ) ) { + * do { + * Per_CPU_Control *cpu_self = _Per_CPU_Get_snapshot(); + * + * if ( cpu_self->dispatch_necessary ) { + * heir = _Thread_Get_heir_and_make_it_executing( cpu_self ); + * } + * } while ( test_and_set( &heir->is_executing ) ); + * } + * + * restore( heir ); + * } + * @endcode */ volatile bool is_executing; #endif |