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Optimize function calls by reducing inherit vars heap allocations and copies

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* Convert `function_get_inherit_vars()` to return a reference to the
  (possibly) existing map, rather than a copy;
* Preallocate and reuse a static (read-only) map for the (very) common
  case of no inherited vars;
* Pass references to the inherit vars map around thereafter, never
  triggering the map copy (or even move) constructor.

NB: If it turns out the reference is unsafe, we can switch the inherit vars
to be a shared_ptr and return that instead.
This commit is contained in:
Mahmoud Al-Qudsi
2019-04-13 11:26:10 -05:00
parent 56125f73e4
commit cdce8511a1
4 changed files with 7 additions and 5 deletions
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6
src/function.cpp
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@@ -257,10 +257,12 @@ bool function_get_definition(const wcstring &name, wcstring &out_definition) {
return func != NULL;
}
std::map<wcstring, env_var_t> function_get_inherit_vars(const wcstring &name) {
const std::map<wcstring, env_var_t> &function_get_inherit_vars(const wcstring &name) {
static const std::map<wcstring, env_var_t> empty_inherit_vars;
scoped_rlock locker(functions_lock);
const function_info_t *func = function_get(name);
return func ? func->inherit_vars : std::map<wcstring, env_var_t>();
return func ? func->inherit_vars : empty_inherit_vars;
}
bool function_get_desc(const wcstring &name, wcstring &out_desc) {