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.)
i'll alter the rte api to use fixed width uint32_t for thread result. it
seems like an unnecessary feature to return a pointer and it can be
accomplished through void *arg if necessary.
>
> > +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?
it's not clear what you mean, can you explain? maybe there is some
context i am missing from the original patch series?
> > +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.
beyond this point free(ctx) will happen in thread_func_wrapper. i will
add a comment to make it clear.
thanks.
