Yedidya Feldblum

This commit performs a **maintenance update** to the **`somerge` system** by **recomputing and regenerating** the `folly/somerge_defs.bzl` definition file. Specifically, it **removes several entries** from both the base and extended native library merge maps. This ensures the `somerge` tool's configurations are up-to-date, impacting which native libraries are considered for merging within projects utilizing `folly`.

This commit **fixes a flaky test** in `folly/memory/test/ArenaTest.cpp` that specifically targeted `Arena::clear()`, which exhibited a ~23% failure rate. The flakiness was caused by an inconsistent initial state of the `Arena` between test iterations, leading to different memory allocation paths and thus varying addresses for subsequent allocations. To resolve this, the **test fix** now primes the `Arena` with a small allocation and a `clear()` operation before the main test loop. This ensures a consistent starting state for the `Arena`'s internal pointers, **improving the reliability and determinism of the `Arena` test suite**.

This commit provides a **bug fix** for a **flaky test** within the **`AtomicHashMap`** module, specifically addressing the `threadEraseInsertRace` test. An **unsigned integer underflow** in the `testEraseEraseThread` synchronization logic, where `currentLevel - lag < i` could wrap around, caused erase threads to prematurely exit and fail to clear the map. The fix changes the condition to `currentLevel < i + lag` to prevent this underflow and also **resets `insertedLevel`** for improved test isolation. This **maintenance** improvement ensures the `AtomicHashMap`'s concurrent erase/insert operations are reliably validated across various build configurations, preventing false negatives.

This commit **fixes a build failure** in the **CI system** by **removing an unsupported platform configuration** from the `folly/system/arch/test/BUCK` file. Specifically, it eliminates the `ci.windows(ci.aarch64())` label, which caused errors due to the absence of a Windows AArch64 platform definition in `platform_utils.bzl`. This **maintenance change** ensures that the `x86_test` can now be built and executed successfully on all other supported architectures, as the test itself is designed to handle non-x86 platforms gracefully. The scope is limited to this specific test's CI configuration, resolving a unique build system incompatibility.

This commit performs a significant **refactoring** to enhance the **type safety** and static analysis coverage of the **Folly Python test suite**. It primarily focuses on `folly/python/test/coro.py`, where comprehensive type annotations are added to all methods within the `FuturesTest` class, and the `pyre-unsafe` directive is removed. Additionally, a new type stub file, `folly/python/test/simplebridgecoro.pyi`, is introduced to provide type information for the `simplebridgecoro` module, with the `BUCK` file updated to include it. This work improves the maintainability and reliability of the **Folly Python coroutine tests** by enabling stricter static analysis with Pyre.

This commit introduces a **new capability** to the **`folly/json/bser`** library by adding a **depth bound** for BSER deserialization. It provides new `parseBser` overloads and a `bser_deserialization_options` struct, allowing callers to specify a maximum recursion depth. The core deserialization logic in `Load.cpp` is updated to enforce this limit, modifying functions like `decodeArray`, `decodeObject`, and `decodeTemplate` to track `remaining_depth`. This enhancement prevents potential stack overflows or excessive resource consumption when processing deeply nested or malicious BSER data, significantly improving the **robustness and security** of BSER parsing.

This commit **fixes a compiler warning** in the **AsyncUDPSocket** component by correcting a preprocessor directive. Specifically, it changes `_WIN32` to `defined(_WIN32)` within `folly/io/async/AsyncUDPSocket.cpp`. This **maintenance fix** addresses a `warning undef` that would otherwise be triggered when the `_WIN32` macro is not defined. The change improves build hygiene and prevents potential issues on various platforms where this macro might not be implicitly defined.

This commit significantly **improves the robustness** of the **`ThreadPoolExecutor`** family by implementing **exception-safe rollback** mechanisms. If thread creation fails within `ThreadPoolExecutor::addThreads` or `ThreadPoolExecutor::setNumThreads`, the pool now reverts to its prior state, preventing inconsistent configurations. This **bug fix** introduces new `initBaton` and `readyBaton` members to the `Thread` struct and updates the `threadRun` logic across `CPUThreadPoolExecutor`, `EDFThreadPoolExecutor`, `IOThreadPoolExecutor`, and `MuxIOThreadPoolExecutor` implementations. The changes ensure greater **stability and reliability** in thread pool management, preventing potential deadlocks or crashes during thread provisioning. New test cases have been added to verify this critical rollback behavior.

This commit performs **code cleanup** within the **networking/asynchronous I/O** subsystem by **removing unused header includes** from `AsyncSSLSocket.cpp`. Specifically, it eliminates `#include <fcntl.h>` and `#include <sys/types.h>`, as the symbols they provide are already available through other included headers. This **maintenance** task improves the codebase's clarity and slightly reduces compilation overhead, with no functional impact on the `AsyncSSLSocket` component.

This commit **refactors** the **`folly::executors`** library by marking various **observer callback methods** and internal thread management functions within `ThreadPoolExecutor` and `IOThreadPoolExecutor` as `noexcept`. Specifically, methods such as `threadStarted`, `threadStopped`, `registerEventBase`, and `handleObserverRegisterThread` are now guaranteed not to throw exceptions. This **maintenance** change enforces a stricter contract for observer implementations, simplifying error handling within the core executor logic and **improving the overall reliability and predictability** of thread pool operations. It ensures that the observed behavior does not need to account for failures originating from the observer callbacks themselves, thereby enhancing the robustness of the executor framework.

This commit **refactors** the **`folly::io::Cursor`** utility by modifying its `write`, `writeBE`, and `writeLE` template methods. These methods now explicitly require a type parameter `T` that matches the value's type `V`, effectively **preventing implicit integer promotion**. This change addresses a potential source of bugs where unintended data sizes could be written to buffers, such as a 32-bit store instead of a 16-bit store. By enforcing explicit type specification, the commit significantly improves the **type safety and correctness** of data serialization operations within `folly::io`.

This commit performs **code cleanup** by removing a **duplicate include** of `folly/io/SocketOptionMap.h` from the `AsyncUDPSocket.cpp` file. The header was erroneously included twice, once before the primary header and again in its correct alphabetical position within the Folly includes block. This **maintenance** task improves **code hygiene** within the **networking/IO** component, specifically for UDP socket handling, without altering any functional behavior or introducing new capabilities.

This commit **enhances data integrity and correctness** by updating various test files to use **explicit types** when calling `Cursor::write` methods. It addresses a potential **bug** where implicit integer promotion could lead to incorrect data sizes being written, such as a 16-bit value being stored as 32 bits. Specifically, test cases within `folly/io/async/test/AsyncSSLSocketTest.cpp`, `folly/io/test/IOBufCursorTest.cpp`, `folly/io/test/IOBufCursorBenchmark.cpp`, and `folly/io/test/QueueAppenderBenchmark.cpp` are modified to use explicit casts or template types for `write`, `writeLE`, and `writeBE`. This **maintenance** change prevents subtle data corruption by ensuring values are written with their intended precision, improving the reliability of I/O operations.

This commit **removes the legacy alias** `folly::hardware_concurrency()` from the Folly library, completing its deprecation. All internal usages of this function have been successfully migrated to `folly::available_concurrency()`, including an update within the **ZSTD compression context pool initialization** in `folly/compression/CompressionContextPoolSingletons.cpp`. This **maintenance refactoring** streamlines the API by eliminating an unnecessary alias, improving the long-term maintainability of **Folly's concurrency and compression utilities**. The change has no functional impact as all call sites now use the preferred function.

This commit performs a **maintenance update** by recomputing and regenerating the Bazel merge maps located in `folly/somerge_defs.bzl`. The **`somerge_maps`** are updated to include a new 'bits' entry, while simultaneously removing several outdated synchronization and symbolizer-related entries. This **chore** ensures that the `folly` build system utilizes the most current and accurate merge definitions, reflecting necessary adjustments in the project's build configuration.

This commit **fixes a build regression** on **non-Linux platforms** within the `folly/system/os` module. It addresses an issue introduced by a recent change that moved the `openat2` wrapper, causing compilation failures on operating systems other than Linux. Specifically, it modifies `folly/system/os/linux.cpp` to **conditionally include** the Linux-specific header `<linux/openat2.h>`, ensuring it is only processed when building on Linux. This **maintenance fix** restores the ability to build the `folly` library successfully across various non-Linux environments.

This commit **optimizes performance** within the **`ThrottledLifoSem` synchronization primitive** by eliminating false sharing. It **refactors** the internal structure to ensure the frequently accessed `state_` atomic variable resides on a separate cacheline from the `mutex_` and `waiters_` members. By adding `alignas(cacheline_align_v)` to `mutex_`, this change prevents unnecessary cross-core cache invalidations and snooping, which previously occurred when slow-path operations modified `mutex_`/`waiters_`. This significantly **improves throughput and reduces latency** for highly concurrent applications utilizing `ThrottledLifoSem`.

This commit performs **maintenance** by **addressing various GCC compiler warnings** and **fixing minor logical issues** across the `folly` library. It includes initializing `PyObject` pointers in `folly/python/error.cpp` to prevent uninitialized variable warnings and correcting an array index in `folly/synchronization/test/HazptrBench.cpp`. Warning suppression pragmas were added to `folly/container/small_vector.h` and an assertion was replaced with an assumption in `folly/FBString.h`. Furthermore, numerous test files were updated to remove GCC warning disable pragmas and use correct self-move assignment syntax, collectively improving code hygiene and ensuring cleaner compilation without altering public API behavior.

This commit introduces a **breaking change** to the **`folly/io/Cursor.h`** API by modifying the `Writable` and `QueueAppender`'s `write`, `writeBE`, and `writeLE` methods to **require an explicit type parameter**. This **bug fix** prevents silent data corruption caused by implicit integer promotion, where a smaller type might be unexpectedly written as a larger 32-bit value. The change ensures that users explicitly specify the intended size of data to be written, improving type safety and preventing subtle errors in **data serialization**. Consequently, several **test files** across `folly/io` were updated to reflect this new explicit type requirement.

This commit primarily **refactors** the **`folly::system::os`** subsystem by relocating the `openat2` syscall wrapper to `folly/system/os/linux.h` and `folly/system/os/linux.cpp`. The functionality is now exposed as the namespaced C++ function `folly::linux_syscall_openat2`, improving code organization and preventing potential name conflicts for Linux-specific system utilities. This **maintenance** effort involved creating a new `BUCK` target for the `linux` library to support the move. Additionally, a minor **maintenance** update was applied to `folly/FixedString.h` to adjust GCC array-bounds warning suppression for version 14.