Point-To-Point Synchronization#

The following section discusses Intel® SHMEM interfaces that provide a mechanism for synchronization between two PEs based on the value of a symmetric data object. The point-to-point synchronization routines can be used to portably ensure that memory access operations observe remote updates in the order enforced by the initiator PE.

The point-to-point synchronization routines support values (the ivar and cmp_value arguments) having a type in the Standard AMO Types Table.

The point-to-point synchronization interface provides named constants whose values are integer constant expressions that specify the comparison operators used by the ishmem synchronization routines. The constant names and associated operations are presented in Table Point-to-point Comparison Constants.

Point-to-point Comparison Constants

Constant Name

Comparison

ISHMEM_CMP_EQ

Equal

ISHMEM_CMP_NE

Not equal

ISHMEM_CMP_GT

Greater than

ISHMEM_CMP_GE

Greater than or equal to

ISHMEM_CMP_LT

Less than

ISHMEM_CMP_LE

Less than or equal to

ISHMEM_WAIT_UNTIL#

Wait for a variable on the local PE to change.

Below, TYPE is one of the standard AMO types and has a corresponding TYPENAME specified by Table Standard AMO Types.

void ishmem_TYPENAME_wait_until(TYPE *ivar, int cmp, TYPE cmp_value)#
Parameters:

  • ivar – Symmetric address of a remotely accessible data object. The type of ivar should match the TYPE and TYPENAME according to the table of Standard AMO Types.

  • cmp – A comparison operator from Table Point-to-point Comparison Constants that compares ivar with cmp_value.

  • cmp_value – The value to be compared with ivar. The type of cmp_value should match the TYPE and TYPENAME according to the table of Standard AMO Types.

Callable from the host and the device.

Description: The ishmem_wait_until operation blocks until the value contained in the symmetric data object, ivar, at the calling PE satisfies the wait condition. The ivar object at the calling PE may be updated by an AMO performed by a thread located within the calling PE or within another PE.

These routines can be used to implement point-to-point synchronization between PEs or between threads within the same PE. A call to ishmem_wait_until blocks until the value of ivar at the calling PE satisfies the wait condition specified by the comparison operator, cmp, and comparison value, cmp_value.

Implementations must ensure that ishmem_wait_until does not return before the update of the memory indicated by ivar is fully complete.

ISHMEMX_WAIT_UNTIL_WORK_GROUP#

Wait for a variable on the local PE to change.

Below, TYPE is one of the standard AMO types and has a corresponding TYPENAME specified by Table Standard AMO Types.

template<typename Group>
void ishmemx_TYPENAME_wait_until_work_group(TYPE *ivar, int cmp, TYPE cmp_value)#
Parameters:

  • ivar – Symmetric address of a remotely accessible data object. The type of ivar should match the TYPE and TYPENAME according to the table of Standard AMO Types.

  • cmp – A comparison operator from Table Point-to-point Comparison Constants that compares ivar with cmp_value.

  • cmp_value – The value to be compared with ivar. The type of cmp_value should match the TYPE and TYPENAME according to the table of Standard AMO Types.

  • group – The SYCL group or sub_group on which to collectively perform the wait operation.

Callable from the device.

Description: The ishmemx_wait_until_work_group operation blocks until the value contained in the symmetric data object, ivar, at the calling PE satisfies the wait condition. The ivar object at the calling PE may be updated by an AMO performed by a thread located within the calling PE or within another PE.

These routines can be used to implement point-to-point synchronization between PEs or between threads within the same PE. A call to ishmemx_wait_until_work_group blocks until the value of ivar at the calling PE satisfies the wait condition specified by the comparison operator, cmp, and comparison value, cmp_value.

Implementations must ensure that ishmemx_wait_until_work_group does not return before the update of the memory indicated by ivar is fully complete.

ISHMEM_TEST#

Indicate whether a variable on the local PE meets the specified condition.

Below, TYPE is one of the standard AMO types and has a corresponding TYPENAME specified by Table Standard AMO Types.

int ishmem_TYPENAME_test(TYPE *ivar, int cmp, TYPE cmp_value)#
Parameters:

  • ivar – Symmetric address of a remotely accessible data object. The type of ivar should match the TYPE and TYPENAME according to the table of Standard AMO Types.

  • cmp – A comparison operator from Table Point-to-point Comparison Constants that compares ivar with cmp_value.

  • cmp_value – The value to be compared with ivar. The type of cmp_value should match the TYPE and TYPENAME according to the table of Standard AMO Types.

Returns:

ishmem_test returns 1 if the comparison of the symmetric object pointed to by ivar with the value cmp_value according to the comparison operator cmp evaluates to true; otherwise, it returns 0.

Callable from the host and device.

Description: ishmem_test tests the numeric comparison of the symmetric object pointed to by ivar with the value cmp_value according to the comparison operator cmp. The ivar object at the calling PE may be updated by an AMO performed by a thread located within the calling PE or within another PE.

Implementations must ensure that ishmem_test does not return 1 before the update of the memory indicated by ivar is fully complete.

ISHMEMX_TEST_WORK_GROUP#

Indicate whether a variable on the local PE meets the specified condition.

Below, TYPE is one of the standard AMO types and has a corresponding TYPENAME specified by Table Standard AMO Types.

int ishmemx_TYPENAME_test_work_group(TYPE *ivar, int cmp, TYPE cmp_value)#
Parameters:

  • ivar – Symmetric address of a remotely accessible data object. The type of ivar should match the TYPE and TYPENAME according to the table of Standard AMO Types.

  • cmp – A comparison operator from Table Point-to-point Comparison Constants that compares ivar with cmp_value.

  • cmp_value – The value to be compared with ivar. The type of cmp_value should match the TYPE and TYPENAME according to the table of Standard AMO Types.

  • group – The SYCL group or sub_group on which to collectively perform the wait operation.

Returns:

ishmem_test returns 1 if the comparison of the symmetric object pointed to by ivar with the value cmp_value according to the comparison operator cmp evaluates to true; otherwise, it returns 0.

Callable from the device.

Description: ishmemx_test_work_group tests the numeric comparison of the symmetric object pointed to by ivar with the value cmp_value according to the comparison operator cmp. The ivar object at the calling PE may be updated by an AMO performed by a thread located within the calling PE or within another PE.

Implementations must ensure that ishmemx_test_work_group does not return 1 before the update of the memory indicated by ivar is fully complete.