[Openmp-dev] Detached tasks behavior changed

[Shilei Tian via Openmp-dev]

Hi Raúl,

Thanks for your report. I’ll fix it soon.

Regards,
Shilei

> On Feb 1, 2021, at 3:48 AM, Raúl Peñacoba Veigas via Openmp-dev <openmp-dev at lists.llvm.org> wrote:
> 
> Hi everyone,
> 
> I've noticed in 9d64275a the behavior of detached tasks has changed. From this commit now the runtime does not taskwait the detached task until completion. If I understand correctly, detached tasks behave like a proxy task, and proxy tasks are taskwaited until completion.
> 
> I attach test that creates a detached or proxy task that performs a sleep to check that the master thread stays in the taskwait.
> 
> // test.c
> 
> #if !defined(DETACH) && !defined(PROXY)
> #error Use -DDETACH or -DPROXY to compile the test
> #endif
> 
> #include <stdio.h>
> #include <pthread.h>
> #include <omp.h>
> #include <unistd.h>
> 
> // detached
> #define PTASK_FLAG_DETACHABLE 0x40
> // proxy
> #define PTASK_FLAG_PROXY 0x10
> 
> // OpenMP RTL interfaces
> typedef long long kmp_int64;
> 
> typedef struct ID {
>   int reserved_1;
>   int flags;
>   int reserved_2;
>   int reserved_3;
>   char *psource;
> } id;
> 
> // Compiler-generated code (emulation)
> typedef struct ident {
>   void* dummy; // not used in the library
> } ident_t;
> 
> typedef enum kmp_event_type_t {
>   KMP_EVENT_UNINITIALIZED = 0,
>   KMP_EVENT_ALLOW_COMPLETION = 1
> } kmp_event_type_t;
> 
> typedef struct {
>   kmp_event_type_t type;
>   union {
>     void *task;
>   } ed;
> } kmp_event_t;
> 
> typedef struct shar { // shareds used in the task
> } *pshareds;
> 
> typedef struct task {
>   pshareds shareds;
>   int(*routine)(int,struct task*);
>   int part_id;
> // void *destructor_thunk; // optional, needs flag setting if provided
> // int priority; // optional, needs flag setting if provided
> // ------------------------------
> // privates used in the task:
>   omp_event_handle_t evt;
> } *ptask, kmp_task_t;
> 
> typedef int(* task_entry_t)( int, ptask );
> 
> #ifdef __cplusplus
> extern "C" {
> #endif
> extern int  __kmpc_global_thread_num(void *id_ref);
> extern int** __kmpc_omp_task_alloc(id *loc, int gtid, int flags,
>                                    size_t sz, size_t shar, task_entry_t rtn);
> extern int __kmpc_omp_task(id *loc, kmp_int64 gtid, kmp_task_t *task);
> extern void __kmpc_proxy_task_completed_ooo ( kmp_task_t *ptask );
> extern omp_event_handle_t __kmpc_task_allow_completion_event(
>                               ident_t *loc_ref, int gtid, kmp_task_t *task);
> #ifdef __cplusplus
> }
> #endif
> 
> int volatile checker;
> 
> void *target(void *task)
> {
>     sleep( 3 );
>     checker = 1;
> #ifdef DETACH
>     omp_fulfill_event(((ptask)task)->evt);
> #endif
> #ifdef PROXY
>     __kmpc_proxy_task_completed_ooo((ptask)task);
> #endif
>     return NULL;
> }
> 
> pthread_t target_thread;
> 
> // User's code
> int task_entry(int gtid, ptask task)
> {
>     pthread_create(&target_thread, NULL, &target, task);
>     return 0;
> }
> 
> int main() {
>   int gtid = __kmpc_global_thread_num(NULL);
>   ptask task;
>   checker = 0;
>   omp_event_handle_t evt;
> /*
>   #pragma omp task detach(evt)
>   {}
> */
> #ifdef DETACH
>   printf("detaching...\n");
>   task = (ptask)__kmpc_omp_task_alloc(NULL,gtid,PTASK_FLAG_DETACHABLE,
>                     sizeof(struct task),sizeof(struct shar),&task_entry);
>   evt = (omp_event_handle_t)__kmpc_task_allow_completion_event(NULL,gtid,task);
>   task->evt = evt;
> #endif
> #ifdef PROXY
>   printf("proxifying...\n");
>   task = (ptask)__kmpc_omp_task_alloc(NULL,gtid,PTASK_FLAG_PROXY,
>                     sizeof(struct task),sizeof(struct shar),&task_entry);
> #endif
>   __kmpc_omp_task(NULL, gtid, task);
>   #pragma omp taskwait
> 
>   // check results
>   if (checker == 1) {
>     printf("passed\n");
>     return 0;
>   } else {
>     printf("failed\n");
>     return 1;
>   }
> }
> 
> // end test.c
> 
> To use detached or proxy task use -DDETACH or -DPROXY in the compilation line.
> 
> The source line that is performing that behavior is https://github.com/llvm/llvm-project/blob/main/openmp/runtime/src/kmp_tasking.cpp#L1274 . Previously the code was https://github.com/llvm/llvm-project/blob/357eea6e8bf78a822b8d3a6fe3bc6f85fee66a3e/openmp/runtime/src/kmp_tasking.cpp#L1236 .
> 
> Regards,
> 
> Raúl
> 
> 
> 
> http://bsc.es/disclaimer
> _______________________________________________
> Openmp-dev mailing list
> Openmp-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/openmp-dev

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/openmp-dev/attachments/20210201/800afcef/attachment.html>