On Tue, Jun 30, 2020 at 12:01 PM Johannes Schindelin <Johannes.Schindelin@xxxxxx> wrote: > > Hi Matheus, > > I am fine with the Windows changes (although I have to admit that I did > not find time to test things yet). > > There is one problem in that I do not necessarily know that the memory is > released correctly when threads end; You will notice that the > `pthread_key_create()` shim in `compat/win32/pthread.h` does not use the > `destructor` parameter at all. The documentation at > > https://docs.microsoft.com/en-us/windows/win32/procthread/using-thread-local-storage > > is also not terribly clear _how_ the memory is released that was assigned > via `TlsSetValue()`. Yes, I wasn't sure about that either... It would be great if someone familiar with TLS memory on Windows could help us with this. > A couple more things: > > On Fri, 26 Jun 2020, Matheus Tavares wrote: > > [...] > > +struct hexbuf_array { > > + int idx; > > Is there a specific reason why you renamed `bufno` to `idx`? If not, I'd > rather keep the old name. OK, I'll change it back in v3. > > + char bufs[4][GIT_MAX_HEXSZ + 1]; > > +}; > > + > > +#ifdef HAVE_THREADS > > +static pthread_key_t hexbuf_array_key; > > +static pthread_once_t hexbuf_array_once = PTHREAD_ONCE_INIT; > > + > > +static void init_hexbuf_array_key(void) > > +{ > > + if (pthread_key_create(&hexbuf_array_key, free)) > > + die(_("failed to initialize threads' key for hash to hex conversion")); > > +} > > + > > +#else > > +static struct hexbuf_array default_hexbuf_array; > > +#endif > > + > > char *hash_to_hex_algop(const unsigned char *hash, const struct git_hash_algo *algop) > > { > > - static int bufno; > > - static char hexbuffer[4][GIT_MAX_HEXSZ + 1]; > > - bufno = (bufno + 1) % ARRAY_SIZE(hexbuffer); > > - return hash_to_hex_algop_r(hexbuffer[bufno], hash, algop); > > + struct hexbuf_array *ha; > > + > > +#ifdef HAVE_THREADS > > + void *value; > > + > > + if (pthread_once(&hexbuf_array_once, init_hexbuf_array_key)) > > + die(_("failed to initialize threads' key for hash to hex conversion")); > > + > > + value = pthread_getspecific(hexbuf_array_key); > > + if (value) { > > + ha = (struct hexbuf_array *) value; > > + } else { > > + ha = xmalloc(sizeof(*ha)); > > + if (pthread_setspecific(hexbuf_array_key, (void *)ha)) > > + die(_("failed to set thread buffer for hash to hex conversion")); > > + } > > +#else > > + ha = &default_hexbuf_array; > > +#endif > > This introduces two ugly `#ifdef HAVE_THREADS` constructs which are > problematic because they are the most likely places to introduce compile > errors. > > I wonder whether you considered introducing a function (and probably a > macro) that transparently gives you a thread-specific instance of a given > data type? The caller would look something like > > struct hexbuf_array *hex_array; > > GET_THREADSPECIFIC(hex_array); > > where the macro would look somewhat like this: > > #define GET_THREADSPECIFIC(var) \ > if (get_thread_specific(&var, sizeof(var)) < 0) > die(_("Failed to get thread-specific %s"), #var); > > and the function would allocate and assign the variable. Hmm, we would need two macros, wouldn't we? GET_THREADSPECIFIC(var) and a DECLARE_THREADSPECIFIC(var, destructor), to declare the pthread_once_t and pthread_key_t variables, as well as define a initialization function for the key (i.e. the callback to pthread_once()). Or we could provide these declarations ourselves, but then we would need the "ifdef HAVE_THREADS" guard to avoid calling pthread_key_create() when there is no multithreading. I think that would work, yes. Alternatively, I think we could adjust the dummy pthread_key_* functions in thread-utils.h to emulate the real ones when HAVE_THREADS == false. Then we could eliminate the `#ifdef HAVE_THREADS` guards and use the same code for both cases here (and everywhere else pthread_key is used). I haven't thought about it carefully enough yet, but I think this *might* be as simple as adding the following defines in the "#ifdef NO_PTHREADS" section of thread-utils.h: #define pthread_key_t void * /* * The destructor is not used in this case as the main thread will only * exit when the program terminates. */ #define pthread_key_create(key_ptr, unused) return_0((*key_ptr) = NULL) #define pthread_setspecific(key, value) return_0((key) = (value)) #define pthread_getspecific(key) (key) #define pthread_key_delete(key) return_0(NULL) static inline int return_0(void *unused) { return 0; } That's the general idea, but we might as well define a `struct dummy_pthread_key_t` instead of defining the key directly as `void *` (and have functions instead of macros). This way we could store, e.g., an "initialized" flag that could be used to return an error code on double-initializations. What do you think?
