callback - Add size-limited function-object overloads to Callback #2851
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retest uvisor |
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/morph test-nightly |
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@mbed-bot: TEST HOST_OSES=ALL |
Result: FAILUREYour command has finished executing! Here's what you wrote!
Outputmbed Build Number: 983 Build failed! |
This allows additional attributes to be attached to the internally
generated type such as move and destructor operations with no increase
in RAM footprint.
The current overloads can't take advantage of this, but it does open
the possibility for more powerful overloads that can provide these
additional attributes.
Changes to mbed-os memory consumption:
.text .data .bss
before 57887 2292 7692
after 57842 2292 7691
The callback class can now accept generalized function-objects:
class Thing {
public:
int value;
void operator()() {
printf("hi! %d\n", value);
}
};
Callback<void()> cb(Thing(2));
However, with the intention of avoiding implicit dynamic-memory
allocations, the Callback class is limited to a single word of storage.
Exceeding this size will eliminate the function-object type from the
overload set and fail to compile.
Effort was invested to make this situation very clear to the user. Here
is an example error message with noise removed:
[ERROR] ./main.cpp: In function 'int main()':
./mbed-os/hal/api/Ticker.h:101:10: note:
no known conversion for argument 1 from 'BigFunc' to 'mbed::Callback<void()>'
The real benefit of this change is the ability for users to hook into
the attributes of the Callback class. This mostly allows lifetime
management of the function-objects from third-party libraries (such as
the Event class from mbed-events).
Note: The convenient `callback` function may become ambiguous if
provided with a type that defines multiple incompatible `operator()`
member functions.
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Looks like I accidentally let gcc-specific struct initialiers in. Updated and tested locally with GCC and ARMCC. /morph test |
Result: FAILUREYour command has finished executing! Here's what you wrote!
Outputmbed Build Number: null Examples Build failed! |
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/morph test |
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Just FYI, I was making a change in the CI config that caused the above test failure, please ignore it! |
Result: SUCCESSYour command has finished executing! Here's what you wrote!
Outputmbed Build Number: 986 All builds and test passed! |
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[Build 995] |
The callback class can now accept generalized function-objects:
However, with the intention of avoiding implicit dynamic-memory allocations, the Callback class is limited to a single word of storage. Exceeding this size will eliminate the function-object type from the
overload set and fail to compile.
Effort was invested to make this situation very clear to the user. Here is an example error message with noise removed:
The real benefit of this change is the ability for users to hook into the attributes of the Callback class. This mostly allows lifetime management of the function-objects from third-party libraries (such as
the Event class from mbed-events).
Note: The convenient
callbackfunction may become ambiguous if provided with a type that defines multiple incompatibleoperator()member functions.Changes to mbed-os memory consumption:
Viewable diff of the zero-argument Callback:
https://www.diffchecker.com/bxWky06j
extra thanks to @pan- and @bogdanm for input on this patch
cc @pan-, @bogdanm, @sg-