Fix memory leaks in exception handling for defer, finally, and async join#436
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nbeerbower wants to merge 1 commit into
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Fix memory leaks in exception handling for defer, finally, and async join#436nbeerbower wants to merge 1 commit into
nbeerbower wants to merge 1 commit into
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Fix three memory management issues: 1. try/finally: When finally block throws/returns, the saved exception and return values were lost without being released. Now properly retains saved values before finally executes and releases them appropriately based on control flow outcome. 2. defer stack: When a deferred call throws while an exception is pending, the original exception was lost without being released. Now properly retains the saved exception and releases it if the defer throws a new exception. 3. task join: When joining a task that threw an exception, the exception_state was copied without retaining the exception_value, leading to incorrect refcounting. Now retains the exception value when copying from task to caller context. https://claude.ai/code/session_01DfpaWxNKzvp8vMc6sEhLjC
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Summary
This PR fixes memory leaks in the interpreter's exception handling by properly retaining and releasing exception values when they are copied between execution contexts or saved across control flow statements.
Key Changes
Concurrency (builtin_join): Added
VALUE_RETAIN()when re-throwing an exception from a joined task to prevent premature deallocation since both the task context and caller context hold references to the exception value.Defer Stack Execution: Added
VALUE_RETAIN()when saving the current exception before defer execution, with correspondingVALUE_RELEASE()calls in both success and failure paths to properly manage the reference count.Try-Finally Statements: Added
VALUE_RETAIN()for both saved return and exception values before executing the finally block, withVALUE_RELEASE()calls in both paths (whether finally restores or changes control flow).Test Coverage: Added three new test cases to verify the fixes:
defer_exception_leak.hml: Tests defer throwing while exception is pendingfinally_exception_leak.hml: Tests finally block throwing a new exceptionjoin_exception_refcount.hml: Tests joining a task that threw an exceptionImplementation Details
The fixes follow a consistent pattern: when an exception value is saved and the execution context may change (through defer execution, finally blocks, or async task joining), the value must be explicitly retained to maintain a reference count that accounts for multiple holders. The corresponding release calls ensure the reference count is decremented when the saved value is either restored or discarded.
This prevents use-after-free errors and memory leaks that occurred when exception values were freed prematurely while still being referenced by other contexts.
https://claude.ai/code/session_01DfpaWxNKzvp8vMc6sEhLjC