[PATCH] LLD: Implement our own future and use that for FileArchive::preload().

[Shankar Easwaran]

On 3/3/2015 12:51 PM, Rui Ueyama wrote:
> On Tue, Mar 3, 2015 at 8:53 AM, Shankar Kalpathi Easwaran <
> shankarke at gmail.com> wrote:
>
>> ================
>> Comment at: include/lld/Core/Parallel.h:77
>> @@ +76,3 @@
>> +/// https://gcc.gnu.org/ml/gcc-patches/2014-05/msg01389.html
>> +template<typename T> class Future {
>> +public:
>> ----------------
>> there is only one usage of Future with lld::File, Why do we want to make
>> this a template ?
>
> I didn't plan to implement a future. I first tried to do that all within
> FileArchive using mutex and condition variables, and then realized that
> that's too low-level multi-thread programming which is pretty error-prone.
>
> If you are familiar with multi-thread programming, futures are basic
> building block of high-level multi-thread programming. It's a rendezvous
> point of a producer thread and a consumer thread. I built a basic block
> here. Replacing T of this Future class with File * is weird.
>
>
>> ================
>> Comment at: lib/ReaderWriter/FileArchive.cpp:63-69
>> @@ -62,8 +62,9 @@
>>       {
>>         std::lock_guard<std::mutex> lock(_mutex);
>>         auto it = _preloaded.find(memberStart);
>>         if (it != _preloaded.end()) {
>> -        std::future<const File *> &future = it->second;
>> -        return future.get();
>> +        std::unique_ptr<Future<const File *>> &p = it->second;
>> +        Future<const File *> *future = p.get();
>> +        return future->get();
>>         }
>>       }
>> ----------------
>> The _preloaded map could get resized here ? Can we resize the map in
>> advance since we know how many members are in the archive ?
>>
> There's no such function like resize defined for std::map because of the
> nature of the map. It's a balanced tree, there's no such notion like making
> room for future use.
I was hinting to make this a unordered_map which has a reserve function 
in it.

Shankar Easwaran

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the Linux Foundation