* Tips for improving performance of Python pretty-printer?
@ 2022-01-11 18:00 Antoine Pitrou
2022-01-11 19:22 ` David Blaikie
0 siblings, 1 reply; 2+ messages in thread
From: Antoine Pitrou @ 2022-01-11 18:00 UTC (permalink / raw)
To: gdb
Hello,
I'm implementing a bunch of pretty-printers (in Python) to improve the
debuggability of C++ types in Apache Arrow C++:
https://github.com/apache/arrow/pull/12092
However, I'm seeing performance issues where inspecting even relatively
simple information is quite slow as soon as I use the "natural" way, by
calling public C++ APIs (e.g. object methods) using
`gdb.parse_and_eval()`.
So for now I'm resorting to inspect private implementation details,
even for types I don't control such as `std::string` or `std::vector`.
As an example, I have the following helper code (simplified below for
clarity):
```
class SharedPtr:
def __init__(self, val):
self.val = val
try:
# libstdc++ internals
self._ptr = val['_M_ptr']
except gdb.error:
# fallback for other C++ standard libraries
self._ptr = gdb.parse_and_eval(
f"{for_evaluation(val)}.get()")
def get(self):
return self._ptr
def for_evaluation(val):
"""
Return a parsable form of gdb.Value `val`
"""
ty = gdb.types.get_basic_type(val.type)
if ty.code == gdb.TYPE_CODE_PTR:
# It's already a pointer, can represent it directly
return f"(({ty}) ({val}))"
if val.address is None:
raise ValueError(f"Cannot further evaluate rvalue: {val}")
return f"(* ({ty}*) ({val.address}))"
```
This works fine but:
1) I need to maintain a generic fallback for non-GNU libstdc++
implementations of the C++ standard library
2) The generic fallback (obviously) suffers from the original
performance problem
Is it expected that `gdb.parse_and_eval` has such a poor performance?
(I didn't run any timings, but as a rough estimate I estimate that it
takes around 100 ms for a relatively simple expression)
Regards
Antoine.
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Tips for improving performance of Python pretty-printer?
2022-01-11 18:00 Tips for improving performance of Python pretty-printer? Antoine Pitrou
@ 2022-01-11 19:22 ` David Blaikie
0 siblings, 0 replies; 2+ messages in thread
From: David Blaikie @ 2022-01-11 19:22 UTC (permalink / raw)
To: Antoine Pitrou; +Cc: gdb
One side note: Generally pretty printers should not call into the code
under test - doing so means the pretty printer can't be used when debugging
a core dump, and risks not being usable when the process is corrupted in
some ways, or risks creating corruption/disturbing a reproduction by
executing code in the test program.
On Tue, Jan 11, 2022 at 10:05 AM Antoine Pitrou via Gdb <gdb@sourceware.org>
wrote:
>
> Hello,
>
> I'm implementing a bunch of pretty-printers (in Python) to improve the
> debuggability of C++ types in Apache Arrow C++:
> https://github.com/apache/arrow/pull/12092
>
> However, I'm seeing performance issues where inspecting even relatively
> simple information is quite slow as soon as I use the "natural" way, by
> calling public C++ APIs (e.g. object methods) using
> `gdb.parse_and_eval()`.
>
> So for now I'm resorting to inspect private implementation details,
> even for types I don't control such as `std::string` or `std::vector`.
> As an example, I have the following helper code (simplified below for
> clarity):
>
> ```
> class SharedPtr:
>
> def __init__(self, val):
> self.val = val
> try:
> # libstdc++ internals
> self._ptr = val['_M_ptr']
> except gdb.error:
> # fallback for other C++ standard libraries
> self._ptr = gdb.parse_and_eval(
> f"{for_evaluation(val)}.get()")
>
> def get(self):
> return self._ptr
>
>
> def for_evaluation(val):
> """
> Return a parsable form of gdb.Value `val`
> """
> ty = gdb.types.get_basic_type(val.type)
> if ty.code == gdb.TYPE_CODE_PTR:
> # It's already a pointer, can represent it directly
> return f"(({ty}) ({val}))"
> if val.address is None:
> raise ValueError(f"Cannot further evaluate rvalue: {val}")
> return f"(* ({ty}*) ({val.address}))"
> ```
>
> This works fine but:
>
> 1) I need to maintain a generic fallback for non-GNU libstdc++
> implementations of the C++ standard library
> 2) The generic fallback (obviously) suffers from the original
> performance problem
>
> Is it expected that `gdb.parse_and_eval` has such a poor performance?
> (I didn't run any timings, but as a rough estimate I estimate that it
> takes around 100 ms for a relatively simple expression)
>
> Regards
>
> Antoine.
>
>
>
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