我正在解决一个与从 OpenCL 内核添加单个全局值相关的错误。
考虑这个（过于简单的）例子：
__kernel some_kernel(__global unsigned int *ops) {
unsigned int somevalue = ...; // a non-zero value is assigned here
*ops += somevalue;
}
我通过clCreateBufferand传入一个初始化为零的参数clEnqueueWriteBuffer。我假设在添加值之后，让队列完成并读回它，我会得到一个非零值。
然后我想这可能是一些奇怪的冲突，所以我尝试做一个原子操作：
__kernel some_kernel(__global unsigned int *ops) {
unsigned int somevalue = ...; // a non-zero value is assigned here
atomic_add(ops, somevalue);
}
唉，没有骰子 - 在将值读回主机指针后，它仍然为零。我已经验证了somevalue在内核执行中具有非零值，并且不知所措。
根据要求，创建内存的代码：
unsigned int *cpu_ops = new unsigned int;
*cpu_ops = 0;
cl_mem_flags flags = CL_MEM_READ_WRITE | CL_MEM_COPY_HOST_PTR;
cl_int error;
cl_mem buffer = clCreateBuffer(context, flags, sizeof(unsigned int), (void*)cpu_ops, &error);
// error code check snipped
error = clEnqueueWriteBuffer(queue, buffer, CL_TRUE, 0, sizeof(unsigned int), (void*)cpu_ops, 0, NULL, NULL);
// error code check snipped
// snip: program setup - it checks out, no errors
cl_kernel some_kernel = clCreateKernel(program, "some_kernel", &error);
// error code check snipped
cl_int error = clSetKernelArg(some_kernel, 0, sizeof(cl_mem), &buffer);
// error code check snipped
//global_work_size and local_work_size set elsewhere
cl_int error = clEnqueueNDRangeKernel(queue, some_kernel, 1, NULL, &global_work_size, &local_work_size, 0, NULL, NULL);
// error code check snipped
clFinish(queue);
cl_int error = clEnqueueReadBuffer(queue, buffer, CL_TRUE, 0, sizeof(unsigned int), (void*)cpu_ops, 0, NULL, NULL);
// error code check snipped
// at this point, cpu_ops still has it's initial value (whatever that value might have been set to)'
我跳过了错误检查代码，因为它不会出错。我实际上使用了一堆自定义的帮助函数来发送和接收数据，设置平台和上下文，编译程序等等，所以上面是由适当的帮助器的主体构造的，参数名称更改为说得通。
我相当确定这是我的失误或缺乏理解，但迫切需要对此的投入。