Description

The following fence operations are supported.

void atomic_work_item_fence(cl_mem_fence_flags flags,
                            memory_order order,
                            memory_scope scope)

// Older syntax memory fences are equivalent to atomic_work_item_fence with the
// same flags parameter, memory_scope_work_group scope, and ordering as follows:
void mem_fence(cl_mem_fence_flags flags)        // memory_order_acq_rel
void read_mem_fence(cl_mem_fence_flags flags)   // memory_order_acquire
void write_mem_fence(cl_mem_fence_flags flags)  // memory_order_release

flags must be set to CLK_GLOBAL_MEM_FENCE, CLK_LOCAL_MEM_FENCE, CLK_IMAGE_MEM_FENCE or a combination of these values ORed together; otherwise the behavior is undefined. The behavior of calling atomic_work_item_fence with CLK_IMAGE_MEM_FENCE ORed together with either CLK_GLOBAL_MEM_FENCE or CLK_LOCAL_MEM_FENCE is equivalent to calling atomic_work_item_fence individually for CLK_IMAGE_MEM_FENCE and the other flags. Passing both CLK_GLOBAL_MEM_FENCE and CLK_LOCAL_MEM_FENCE to atomic_work_item_fence will synchronize memory operations to both local and global memory through some shared atomic action, as described in section 3.3.6.2 of the OpenCL Specification.

Depending on the value of order, this operation:

  • has no effects, if order == memory_order_relaxed.

  • is an acquire fence, if order == memory_order_acquire.

  • is a release fence, if order == memory_order_release.

  • is both an acquire fence and a release fence, if order == memory_order_acq_rel.

  • is a sequentially consistent acquire and release fence, if order == memory_order_seq_cst.

For images declared with the read_write qualifier, the atomic_work_item_fence must be called to make sure that writes to the image by a work-item become visible to that work-item on subsequent reads to that image by that work-item.

The use of memory order and scope enumerations must respect the restrictions section below.

See Also

atomicFunctions, atomicTypes, atomic_compare_exchange, atomic_exchange, atomic_fetch_key, atomic_flag, atomic_flag_clear, atomic_flag_test_and_set, atomic_flag_test_and_set_explicit, atomic_init, atomic_load, atomic_store, atomic_work_item_fence

Document Notes

For more information, see the OpenCL C Specification

This page is extracted from the OpenCL C Specification. Fixes and changes should be made to the Specification, not directly.

Copyright

Copyright 2014-2025 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0