[PATCH] Verify source files for a module only once during the build

[Dmitri Gribenko]

On Fri, Feb 7, 2014 at 10:36 PM, Argyrios Kyrtzidis <kyrtzidis at apple.com> wrote:
>
> On Feb 7, 2014, at 1:56 PM, Dmitri Gribenko <gribozavr at gmail.com> wrote:
>
> On Fri, Feb 7, 2014 at 9:54 PM, Argyrios Kyrtzidis <kyrtzidis at apple.com>
> wrote:
>
> On Feb 7, 2014, at 1:46 PM, Dmitri Gribenko <gribozavr at gmail.com> wrote:
>
> On Fri, Feb 7, 2014 at 9:39 PM, Argyrios Kyrtzidis <kyrtzidis at apple.com>
> wrote:
>
> On Feb 7, 2014, at 12:47 PM, Dmitri Gribenko <gribozavr at gmail.com> wrote:
> I wanted to avoid the need to do the atomic-rename dance.
>
> What is you concern with it ?
>
>
> No real concerns, just a bit more code to write.
>
> What is the
> potential for mtime confusion that you see?  We could provide a
> function in libclang to get the current timestamp so that clients
> don't have to invent their own, potentially incorrect way to get it.
>
>
> I really want to reduce complexity here and potential for out-of-sync,
> because now you have
>
>
> 1) The builder needs to provide an increasing timestamp by getting clock
> time (or libclang call ?)
> 2) we will compare that clock time with the file system modification time
> which can come from any kind of underlying file system
>
>
> vs
>
> 1) The builder needs to provide an increasing timestamp
>
>
> I much prefer the latter simpler approach.
>
>
> I can see how clients can break any of these while implementing (1) --
> for example, by using the local time instead of UTC time, and having
> the build happen when the DST adjustment is made.  But (2) is just an
> OS-level thing, it can not go wrong.
>
> Also, imagine that we have a good client build system and a bad client
> build system.  A good client uses correct timestamps, a bad client
> uses timestamps + 1 billion.  Then after the bad client creates a
> module, the good client will never rebuild it, because its timestamps
> will always be "in the past”.
>
>
> A bad client will always be a problem but this is the responsibility of the
> builder, if the builder timestamps are self-consistent we don’t need to
> worry about any time changes or adjustments or what have you, it will not
> even need to be time based, we just don’t care.
>
>
> A bad client will only create a problem for itself if clang uses
> filesystem mtime on the timestamp file.
>
>
> Ok, I retract my objections but with the current approach we definitely need
> a libclang API to control what gets passed in with the option (and provide a
> convenient way to “get it right”), could you add that ?

Sure, will do.  Do you think that we could also add a separate binary
/ a mode in clang to print it to use in build systems that don't embed
libclang?

Dmitri

-- 
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/