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

[Argyrios Kyrtzidis]

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.

> 
> 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>*/