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

[Argyrios Kyrtzidis]

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 ?

> 
> 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>*/

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