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7.2.8 _gfortran_caf_register — Registering coarrays ¶

Description:

Registers memory for a coarray and creates a token to identify the coarray. The routine is called for both coarrays with SAVE attribute and using an explicit ALLOCATE statement. If an error occurs and STAT is a NULL pointer, the function shall abort with printing an error message and starting the error termination. If no error occurs and STAT is present, it shall be set to zero. Otherwise, it shall be set to a positive value and, if not-NULL, ERRMSG shall be set to a string describing the failure. The routine shall register the memory provided in the DATA-component of the array descriptor DESC, when that component is non-NULL, else it shall allocate sufficient memory and provide a pointer to it in the DATA-component of DESC. The array descriptor has rank zero, when a scalar object is to be registered and the array descriptor may be invalid after the call to _gfortran_caf_register. When an array is to be allocated the descriptor persists.

For CAF_REGTYPE_COARRAY_STATIC and CAF_REGTYPE_COARRAY_ALLOC, the passed size is the byte size requested. For CAF_REGTYPE_LOCK_STATIC, CAF_REGTYPE_LOCK_ALLOC and CAF_REGTYPE_CRITICAL it is the array size or one for a scalar.

When CAF_REGTYPE_COARRAY_ALLOC_REGISTER_ONLY is used, then only a token for an allocatable or pointer component is created. The SIZE parameter is not used then. On the contrary when CAF_REGTYPE_COARRAY_ALLOC_ALLOCATE_ONLY is specified, then the token needs to be registered by a previous call with regtype CAF_REGTYPE_COARRAY_ALLOC_REGISTER_ONLY and either the memory specified in the DESC’s data-ptr is registered or allocate when the data-ptr is NULL.

Syntax:

void caf_register (size_t size, caf_register_t type, caf_token_t *token, gfc_descriptor_t *desc, int *stat, char *errmsg, size_t errmsg_len)

Arguments:

size	For normal coarrays, the byte size of the coarray to be allocated; for lock types and event types, the number of elements.
type	one of the caf_register_t types.
token	intent(out) An opaque pointer identifying the coarray.
desc	intent(inout) The (pseudo) array descriptor.
stat	intent(out) For allocatable coarrays, stores the STAT=; may be NULL
errmsg	intent(out) When an error occurs, this will be set to an error message; may be NULL
errmsg_len	the buffer size of errmsg.

NOTES

Nonallocatable coarrays have to be registered prior use from remote images. In order to guarantee this, they have to be registered before the main program. This can be achieved by creating constructor functions. That is what GCC does such that also for nonallocatable coarrays the memory is allocated and no static memory is used. The token permits to identify the coarray; to the processor, the token is a nonaliasing pointer. The library can, for instance, store the base address of the coarray in the token, some handle or a more complicated struct. The library may also store the array descriptor DESC when its rank is non-zero.

For lock types, the value shall only be used for checking the allocation status. Note that for critical blocks, the locking is only required on one image; in the locking statement, the processor shall always pass an image index of one for critical-block lock variables (CAF_REGTYPE_CRITICAL). For lock types and critical-block variables, the initial value shall be unlocked (or, respectively, not in critical section) such as the value false; for event types, the initial state should be no event, e.g. zero.