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fix: Avoid premature release for external pointers #423

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fix: Avoid premature release for external pointers #423

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3e2132e
fix: Avoid premature release for external pointers
krlmlr Dec 7, 2024
09f8524
Merge branch 'main' into b-extptr-leak
krlmlr Oct 2, 2025
51908e8
Add test for external_pointer attribute preservation and fix move ass…
Copilot Jan 22, 2026
6639ef6
Remove
krlmlr Jan 22, 2026
77060f5
Clarify
krlmlr Jan 22, 2026
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krlmlr Jan 22, 2026
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49 changes: 49 additions & 0 deletions cpp11test/src/test-external_pointer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -36,4 +36,53 @@ context("external_pointer-C++") {
uniq.reset();
expect_true(deleted == true);
}

test_that("external_pointer preserves attributes when moved (issue #308)") {
// Test move constructor
{
int* value = new int(42);
cpp11::external_pointer<int> p(value);

// Set an attribute on the external pointer
Rf_setAttrib(p, R_ClassSymbol, Rf_mkString("test_class"));

// Verify attribute exists before move
SEXP class_attr = Rf_getAttrib(p, R_ClassSymbol);
expect_true(class_attr != R_NilValue);

// Move the external pointer using move constructor
cpp11::external_pointer<int> p_moved = std::move(p);

// Verify attribute is preserved after move
SEXP class_attr_after = Rf_getAttrib(p_moved, R_ClassSymbol);
expect_true(class_attr_after != R_NilValue);
expect_true(strcmp(CHAR(STRING_ELT(class_attr_after, 0)), "test_class") == 0);

// Clean up
delete p_moved.release();
}

// Test move assignment operator
{
int* value1 = new int(1);
cpp11::external_pointer<int> p1(value1);

// Set an attribute on p1
Rf_setAttrib(p1, R_ClassSymbol, Rf_mkString("test_class"));

// Create p2 with nullptr (no memory leak)
cpp11::external_pointer<int> p2(nullptr);

// Move assign p1 to p2
p2 = std::move(p1);

// Verify attribute is preserved after move assignment
SEXP class_attr_after = Rf_getAttrib(p2, R_ClassSymbol);
expect_true(class_attr_after != R_NilValue);
expect_true(strcmp(CHAR(STRING_ELT(class_attr_after, 0)), "test_class") == 0);

// Clean up
delete p2.release();
}
}
}
11 changes: 9 additions & 2 deletions inst/include/cpp11/external_pointer.hpp
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Expand Up @@ -66,9 +66,16 @@ class external_pointer {
data_ = safe[Rf_shallow_duplicate](rhs.data_);
}

external_pointer(external_pointer&& rhs) { reset(rhs.release()); }
external_pointer(external_pointer&& rhs) {
data_ = rhs.data_;
rhs.data_ = R_NilValue;
}

external_pointer& operator=(external_pointer&& rhs) noexcept { reset(rhs.release()); }
external_pointer& operator=(external_pointer&& rhs) noexcept {
data_ = rhs.data_;
rhs.data_ = R_NilValue;
Comment on lines +77 to +79
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Copilot AI Jan 22, 2026

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The move assignment operator overwrites data_ without releasing the previously held resource, potentially causing a memory leak. The old data_ should be released before assigning the new value.

Suggested change
data_ = rhs.data_;
rhs.data_ = R_NilValue;
if (this != &rhs) {
if (data_ != R_NilValue) {
r_deleter(data_);
}
data_ = rhs.data_;
rhs.data_ = R_NilValue;
}

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@krlmlr krlmlr Jan 22, 2026

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This is wrong and defeats the purpose of this PR. Added a clarification comment.

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@pachadotdev pachadotdev Jan 23, 2026

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I had no idea about this copilot thing. I will take a look!

Btw, in the cpp4r I ended up doing things a bit different https://github.com/pachadotdev/cpp4r/blob/main/inst/include/cpp4r/external_pointer.hpp

return *this;
}
Comment on lines +74 to +81
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Copilot AI Jan 22, 2026

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The move assignment operator does not handle self-assignment correctly. If this == &rhs, the operation will set data_ to R_NilValue before returning, resulting in a null pointer. Add a self-assignment check at the beginning of the function.

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external_pointer& operator=(std::nullptr_t) noexcept { reset(); };

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