If barrier is inside a conditional statement, then all work-items must enter the conditional if any work-item enters the conditional statement and executes the barrier.

If barrier is inside a loop, all work-items must execute the barrier for each iteration of the loop before any are allowed to continue execution beyond the barrier.

The barrier function also queues a memory fence (reads and writes) to ensure correct ordering of memory operations to local or global memory.

The flags argument specifies the memory address space and can be set to a combination of the following literal values.

CLK_LOCAL_MEM_FENCE - The barrier function will either flush any variables stored in local memory or queue a memory fence to ensure correct ordering of memory operations to local memory.

CLK_GLOBAL_MEM_FENCE - The barrier function will queue a memory fence to ensure correct ordering of memory operations to global memory. This can be useful when work-items, for example, write to buffer or image objects and then want to read the updated data.