+1
Just duplicate it - saves complexity and lowers probability of error
On Feb 5, 2013, at 11:38 AM, George Bosilca <bosi...@icl.utk.edu> wrote:
> The major benefit of the second method is that it has the obvious potential
> to save us some memory. Not much I guess, but somewhere in the order of few
> Kb.
>
> But in order to save this memory, the originator must keep a pointer to the
> data in order to be able to free it after the mca_params framework is closed.
> This means for each string saved (due to the lack of the strdup in the
> mca_params framework), there will be sizeof(char*) bytes spend in
> bookkeeping. Thus the memory savings will be drastically lowered, and the
> benefit of the second approach is strongly compromised.
>
>
> George.
>
> On Feb 5, 2013, at 12:46 , Nathan Hjelm <hje...@lanl.gov> wrote:
>
>> Notes:
>>
>> Variable system currently takes ownership of string values. This is done so
>> strings can be freed when overwritten (by mca_base_var_set_value) or when
>> the variable is deregistered. This requires that initial string values be
>> allocated on the heap (not .DATA, heap, etc). Brian raised a good point that
>> projects/frameworks/components should be responsible for freeing anything
>> they allocate and that it shouldn't be the responsibility of the MCA
>> variable system to free these strings (though we have to handle the
>> mca_base_var_set_value case).
>>
>> Some options:
>> 1) Always duplicate the string passed in by the caller. The caller will have
>> to free the original value if it was allocated. Ex:
>>
>> tmp = strdup ("some_string_value");
>> backing_store = tmp;
>> mca_base_var_register (..., MCA_BASE_VAR_TYPE_STRING, ..., &backing_store);
>> free (tmp);
>>
>> 2) Add a flag indicating whether the variable system should call free on the
>> initial value. Ex:
>>
>> backing_store = "some_string_value";
>> mca_base_var_register (..., MCA_BASE_VAR_TYPE_STRING, ...,
>> MCA_BASE_VAR_FLAG_STATIC, ..., &backing_store);
>>
>> If the STATIC flag is not set the variable system takes ownership of the
>> string and frees it later. If the STATIC flag is set the variable system can
>> either 1) use the initial value, or 2) strdup the initial value. There are
>> issues with using the initial value without duplication since the registree
>> would need to ensure the initial value lives as long as the registered
>> variable (not a problem if the value is in .DATA or .BSS).
>>
>> Thoughts on these options? Other options?
>>
>>
>> List of initial supported types is adequate: char *, int, and bool. We can
>> re-evaluate later if there is a need for more types.
>>
>>
>> We need to figure out how Open MPI could read all file values and build an
>> environment that could be passed to the backend to prevent the need to read
>> from files on the backend. This may necessitate modifying the mca_base_var
>> API.
>>
>>
>> -Nathan
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>
>
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