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Graph/dangling-lambda-reference-capture

AntiPattern

Dangling Lambda Capture

dangling-lambda-reference-capture

Lambda callbacks capture local variables by reference and outlive their scope, so Qt signal handlers later read freed memory, causing access violations; fixing it requires safe ownership (copy/move) or capturing a lifetime-valid object.

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Updated5/4/2026

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30 linked nodes

MATCHESSolution

Treat the selected value as a shared reference (avoid unnecessary cloning/deriving new arrays/objects in selectors). If memory pressure occurs, ensure large datasets are not being copied or accidentally retained (e.g., avoid creating new Float32Array/object instances per render; consider weak caching patterns such as WeakMap only for derived mappings).

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Have you checked what your csv file sizes are? — By default lambda gives you 512 MB of storage but it can go upto 10 GB now. Tension: there is a possibility that the temp storage is getting exceeded. Outcome: Lambda Ephemeral Storage Update.

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Please review my Lambda function code and help me identify the issue? — I have verified the environment variables, IAM permissions, and the input event JSON. Outcome: I suspect there might be an issue with my Lambda function.

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Trigger an AWS Lambda function whenever objects are created — whenever objects are created. Tension: write some code that either operates on the object immediately or writes the object information to a database. Outcome: it can be accessed quickly in future.

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Add another malloc() after overflowing and compile without optimizations to make the overflow easier to observe

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Technically, it's not 100% free of undefined behavior. — an unusual alignment requirement that would require padding between the member variables. Tension: Nevertheless, it should be a reliable example.

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Use smaller scopes where it improves correctness (e.g., declare loop counters inside the loop, such as `for(int i = 0; ...)`), and rely on the compiler/JIT for resource efficiency; avoid broader scopes to reduce the chance of stale or invalid variable usage.

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Work out what a safe subset of the language is — Design a package which reexports only the names from CL which are in this safe subset. Tension: there are snares everywhere. Outcome: Design a safe reader. This should at least prevent read-time evaluation.

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if all you're trying to do is share something between multiple threads — consider using `Arc` instead. Outcome: this implements a thread-safe reference counted smart pointer.

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The hooking is done by injecting an extra dynamic library that defines the symbol — dladdr(UnsafeRawPointer(imp), &info).

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`useCallback` needs to be used — to be used as a callback and thus prevent the unnecessary re-renders. Tension: `memo` can't prevent `ExpensiveComponent` from being re-rendered. Outcome: const handleRender = useCallback(() => {...}, []);.

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Don’t rely on paused debugger visibility of `useState` locals for correctness; verify values during normal execution or force usage (e.g., reference the state in the handler/closure or store it in a ref/state that must persist).

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The changed code invokes undefined behaviour. — Java 25 FFM API. Tension: You can't rely on always getting this behaviour. Outcome: The caller's pointer is passed in to it, but it's never used.

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MemorySegment result = (MemorySegment) hLoadLibraryW.invokeExact(capturedState, lpLibName); — capturedState is the first argument to hLoadLibraryW before the normal args. Tension: This would also work. Outcome: bind the state variable as first arg.

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If you define `aLambda` as follows instead — Since `Notifications.addListener` takes a parameter of type `Notifications.Listener`. Tension: it will not be garbage-collected since the `Listener` object will now have a strong reference held by `aLambda`. Outcome: then its type will be what is required by `addListener` and it will not be garbage-collected.

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If the variable is a final (or effectively final) local variable. Tension: if it was called after the method exited, the lambda wouldn't be able to read or write the (now non-existent!) variable.

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copy and modify the following function in e.g. my main.cpp file — for Qt 6.10. Tension: It disables all accessibility features. Outcome: return false;.

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Capture calls by reference in the lambda so increments affect the original counter

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introduce a filed of `QtClass` and capture `this` — A class member is no option for me. Tension: other answer provided quick fix without thinking about code intent. Outcome: Now `msg` will live as long as instance of `QtClass` lives.

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then the variable should be copied (removing &). Tension: `msg.append(" World")` seems to modify `msg`. Outcome: the lambda must be mutable.

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Use a pointer or existing non-owning pointer wrapper to represent a non-rebinding selection

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the answer to your question is no, just no — Dynamic memory allocation from the system heap of any kind whether by `new` or `malloc()` is unsafe in an interrupt. Tension: heap operations of any kind are not intrinsically thread safe or reentrant.

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Tension: I am not using direct pointers. Outcome: I would change the signature to:.

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unbounded memory allocation (DoS) — processing a crafted ELF file.

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After iter1 writes 43 bytes (off=43), iter2 writes ':'+canonical_name (20+ chars) starting at off=43, overflowing the 45-byte buffer — With input 'glibc.malloc.mxfast=glibc.malloc.mxfast=512' (43 bytes), the buffer is 45 bytes. Tension: overflowing the 45-byte buffer. Outcome: Verified by examining fix commit 1056e5b4c3.

MATCHESSolution

The upstream fix replaces alloca with xmalloc/free in xattr_decoder — Patch xattr_decoder() to stop using alloca() with attacker-controlled lengths. Tension: stop using alloca() with attacker-controlled lengths. Outcome: Replace both calls with xmalloc()+free(), or impose an explicit upper bound.

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Never cache raw pointers into a buffer that may be reallocated.

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after each allocation that may trigger GC. Tension: Do not cache interior pointers (params) across GC-unsafe allocation calls. Outcome: Apply same fix pattern to sampled_data_continue.

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Remove cleanup from calc_ecdh_key() (lines 131-134), making it NOT responsible for freeing parameters — Keep cleanup in callers (_gnutls_proc_ecdh_common_client_kx and _gnutls_gen_ecdh_common_client_kx_int). Tension: Ensure single ownership of resource lifecycle. Outcome: Alternatively, remove caller cleanup and make calc_ecdh_key() the sole cleanup point.

MATCHESSolution

Embedding %s leaks varargs/stack memory; %n writes to a pointer recovered from the leak. — upd_wrtrtl at line 6994. Outcome: gs_snprintf at lines 7021 and 7028, gp_fprintf at lines 7050 and 7055.

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