LazyInit_test Class Reference

Description

Test:

Verify a mix-in to allow for lazy initialisation of complex infrastructure tied to a std::function; the intention is to have a »trap« hidden in the function itself to trigger on first use and perform the one-time initialisation, then finally lock the object at a fixed place.

See also

lazy-init.hpp

lib::RandomDraw

Definition at line 50 of file lazy-init-test.cpp.

Classes
struct	LazyDemo
	elaborate setup used for integration test More...

Private Member Functions
void	run (Arg)
void	verify_trojanLambda ()
void	verify_inlineStorage ()
void	verify_TargetRelocation ()
void	verify_triggerMechanism ()
void	verify_lazyInitialisation ()
void	verify_complexUsageWithCopy ()

Member Function Documentation

run()

void run ( Arg  )

inlineprivate

Definition at line 55 of file lazy-init-test.cpp.

References LazyInit_test::verify_complexUsageWithCopy(), LazyInit_test::verify_inlineStorage(), LazyInit_test::verify_lazyInitialisation(), LazyInit_test::verify_TargetRelocation(), LazyInit_test::verify_triggerMechanism(), and LazyInit_test::verify_trojanLambda().

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verify_trojanLambda()

void verify_trojanLambda ( )

inlineprivate

Test:

verify construction of the »trap« front-end eventually to trigger initialisation

• this test does not involve any std::function, rather a heap-allocated copy of a λ

the <em>target function</em> finally to be invoked performs a verifiable computation

the <em>delegate</em> receives an memory location and returns a reference to the target

the generated <em>»trojan λ«</em> captures its own address, invokes the delegate,

retrieves a reference to a target functor, and finally invokes this with actual arguments.

Remarks

the purpose of this convoluted scheme is for the delegate to perform initialisation, taking into account the current memory location „sniffed“ by the trojan.

Definition at line 79 of file lazy-init-test.cpp.

References TrojanFun< SIG >::generateTrap(), and lib::rani().

Referenced by LazyInit_test::run().

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verify_inlineStorage()

void verify_inlineStorage ( )

inlineprivate

Test:

verify that std::function indeed stores a simple functor inline.

Remarks

The implementation of LazyInit relies crucially on a known optimisation in the standard library ─ which unfortunately is not guaranteed by the standard: Typically, std::function will apply small object optimisation to place a very small functor directly into the wrapper, if the payload has a trivial copy-ctor. Libstdc++ is known to be rather restrictive, while other implementations trade increased storage size of std::function against more optimisation possibilities. LazyInit exploits this optimisation to „spy“ about the current object location, allowing to execute the lazy initialisation on first use, without further help by client code. This trickery seems to be the only way, since λ-capture by reference is broken after copying or moving the host object (typically required for DSL use). In case this turns out to be fragile, LazyInit should become a "LateInit" and needs help by the client or the user to trigger initialisation; alternatively the DSL could be split off into a separate builder object distinct from RandomDraw.

Definition at line 152 of file lazy-init-test.cpp.

References util::isCloseBy().

Referenced by LazyInit_test::run().

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verify_TargetRelocation()

void verify_TargetRelocation ( )

inlineprivate

Test:

verify navigating an object structure by applying known offsets consecutively from a starting point within an remote instance

Remarks

in the real usage scenario, we know only the offset and attempt to find home without knowing the layout.

Definition at line 185 of file lazy-init-test.cpp.

References lib::rani().

Referenced by LazyInit_test::run().

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verify_triggerMechanism()

void verify_triggerMechanism ( )

inlineprivate

Test:

demonstrate the trigger mechanism in isolation

Definition at line 232 of file lazy-init-test.cpp.

References lib::rani().

Referenced by LazyInit_test::run().

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verify_lazyInitialisation()

void verify_lazyInitialisation ( )

inlineprivate

Test:

demonstrate a basic usage scenario

Definition at line 281 of file lazy-init-test.cpp.

References lib::rani().

Referenced by LazyInit_test::run().

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verify_complexUsageWithCopy()

void verify_complexUsageWithCopy ( )

inlineprivate

Test:

use an elaborately constructed example to cover more corner cases

• the function to manage and initialise lazily is a member of the derived class
• the initialisation routine adapts this function and links it with the current object location; thus, invoking this function on a copy would crash / corrupt memory.
• however, as long as initialisation has not been triggered, LazyDemo instances can be copied; they may even be assigned to existing instances, overwriting their state.
• a second given function will be chained behind the first one; this happens immediately if the first function was already invoked (and this initialised)
• but when however both functions are attached immediately, prior to invocation, then an elaborate chain of initialisers is setup behind the scenes and played back in definition order once lazy initialisation is triggered
• all the intermediary state is safe to copy and move and fork

Remarks

11/2023 memory allocations were verified using lib::test::Tracker and the EventLog

Definition at line 386 of file lazy-init-test.cpp.

References LazyInit_test::LazyDemo::attach(), LazyInit_test::LazyDemo::fun, LazyInit< PAR >::isInit(), LazyInit_test::LazyDemo::seed, and VERIFY_ERROR.

Referenced by LazyInit_test::run().

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The documentation for this class was generated from the following file:

• lazy-init-test.cpp