[PATCH v2 2/6] eal: add thread lifetime management

[Tyler Retzlaff]

On Sat, Jun 18, 2022 at 03:59:08PM +0300, Dmitry Kozlyuk wrote:
> 2022-06-14 16:47 (UTC-0700), Tyler Retzlaff:
> > On Windows, the function executed by a thread when the thread starts is
> > represeneted by a function pointer of type DWORD (*func) (void*).
> > On other platforms, the function pointer is a void* (*func) (void*).
> > 
> > Performing a cast between these two types of function pointers to
> > uniformize the API on all platforms may result in undefined behavior.
> > TO fix this issue, a wrapper that respects the signature required by
> > CreateThread() has been created on Windows.
> 
> The interface issue is still there:
> `rte_thread_func` allows the thread routine to have a pointer-sized result.
> `rte_thread_join()` allows to obtain this value as `unsigned long`,
> which is pointer-sized on 32-bit platforms
> and less than that on 64-bit platforms.
> This can lead to issues when developers assume they can return a pointer
> and this works on 32 bits, but doesn't work on 64 bits.
> If you want to keep API as close to phtread as possible,
> the limitation must be at least clearly documented in Doxygen
> (`rte_thread_func` is undocumented BTW).
> I also suggest using `uint32_t` instead of `unsigned long`
> precisely to avoid "is it pointer-sized?" doubts.
> (I don't see much benefit in keeping pthread-like signature.
> When moving from pthread to rte_thread,
> it is as trivial to change the thread routine return type.)

thanks Dmitry, i wasn't aware this feedback had been given previously.
let me digest the problem and we'll figure out how we can address it.

> 
> > +int
> > +rte_thread_create(rte_thread_t *thread_id,
> > +		const rte_thread_attr_t *thread_attr,
> > +		rte_thread_func thread_func, void *args)
> > +{
> > [...]
> > +		if (thread_attr->priority ==
> > +				RTE_THREAD_PRIORITY_REALTIME_CRITICAL) {
> > +			ret = ENOTSUP;
> > +			goto cleanup;
> > +		}
> > +		ret = thread_map_priority_to_os_value(thread_attr->priority,
> > +				&param.sched_priority, &policy);
> > +		if (ret != 0)
> > +			goto cleanup;
> 
> thread_map_priority_to_os_value() already checks for unsupported values,
> why not let it do this particular check?

hm, i hadn't noticed that was duplicated. let me try to eliminate it.

> 
> > +int
> > +rte_thread_join(rte_thread_t thread_id, unsigned long *value_ptr)
> > +{
> > +	int ret = 0;
> > +	void *res = NULL;
> > +	void **pres = NULL;
> > +
> > +	if (value_ptr != NULL)
> > +		pres = &res;
> > +
> > +	ret = pthread_join((pthread_t)thread_id.opaque_id, pres);
> > +	if (ret != 0) {
> > +		RTE_LOG(DEBUG, EAL, "pthread_join failed\n");
> > +		return ret;
> > +	}
> > +
> > +	if (value_ptr != NULL && *pres != NULL)
> > +		*value_ptr = *(unsigned long *)(*pres);
> > +
> > +	return 0;
> > +}
> 
> What makes *pres == NULL special?
> 
> > +static DWORD
> > +thread_func_wrapper(void *args)
> > +{
> > +	struct thread_routine_ctx *pctx = args;
> > +	struct thread_routine_ctx ctx;
> > +
> > +	ctx.thread_func = pctx->thread_func;
> > +	ctx.routine_args = pctx->routine_args;
> 
> ctx = *pctx?

ack

> 
> > +
> > +	free(pctx);
> > +
> > +	return (DWORD)(uintptr_t)ctx.thread_func(ctx.routine_args);
> > +}
> > +
> > +int
> > +rte_thread_create(rte_thread_t *thread_id,
> > +		  const rte_thread_attr_t *thread_attr,
> > +		  rte_thread_func thread_func, void *args)
> > +{
> > +	int ret = 0;
> > +	DWORD tid;
> > +	HANDLE thread_handle = NULL;
> > +	GROUP_AFFINITY thread_affinity;
> > +	struct thread_routine_ctx *ctx = NULL;
> > +
> > +	ctx = calloc(1, sizeof(*ctx));
> > +	if (ctx == NULL) {
> > +		RTE_LOG(DEBUG, EAL, "Insufficient memory for thread context allocations\n");
> > +		ret = ENOMEM;
> > +		goto cleanup;
> > +	}
> > +	ctx->routine_args = args;
> > +	ctx->thread_func = thread_func;
> > +
> > +	thread_handle = CreateThread(NULL, 0, thread_func_wrapper, ctx,
> > +		CREATE_SUSPENDED, &tid);
> > +	if (thread_handle == NULL) {
> > +		ret = thread_log_last_error("CreateThread()");
> > +		free(ctx);
> > +		goto cleanup;
> 
> Missing `free(ctx)` from other error paths below.

ack

> 
> > +	}
> > +	thread_id->opaque_id = tid;
> > +
> > +	if (thread_attr != NULL) {
> > +		if (CPU_COUNT(&thread_attr->cpuset) > 0) {
> > +			ret = convert_cpuset_to_affinity(
> > +							&thread_attr->cpuset,
> > +							&thread_affinity
> > +							);
> > +			if (ret != 0) {
> > +				RTE_LOG(DEBUG, EAL, "Unable to convert cpuset to thread affinity\n");
> > +				goto cleanup;
> > +			}
> > +
> > +			if (!SetThreadGroupAffinity(thread_handle,
> > +						    &thread_affinity, NULL)) {
> > +				ret = thread_log_last_error("SetThreadGroupAffinity()");
> > +				goto cleanup;
> > +			}
> > +		}
> > +		ret = rte_thread_set_priority(*thread_id,
> > +				thread_attr->priority);
> > +		if (ret != 0) {
> > +			RTE_LOG(DEBUG, EAL, "Unable to set thread priority\n");
> > +			goto cleanup;
> > +		}
> > +	}
> > +
> > +	if (ResumeThread(thread_handle) == (DWORD)-1) {
> > +		ret = thread_log_last_error("ResumeThread()");
> > +		goto cleanup;
> > +	}
> > +
> > +cleanup:
> > +	if (thread_handle != NULL) {
> > +		CloseHandle(thread_handle);
> > +		thread_handle = NULL;
> > +	}
> > +
> > +	return ret;
> > +}

thanks let me tidy those bits up, i'll submit a revision this week.