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feat(build): add CONFIG_COMPILER_CXX_ATOMIC_LOCK_POLICY option

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libstdc++ selects between a lock-free and a mutex-based policy for
std::shared_ptr reference counting based on this macro. Enabling this
option forces the lock-free policy, which avoids pulling in the
mutex-based implementation and can reduce code size.

Note: the lock-free policy avoids embedding a mutex in each control
block, saving about 88 bytes per shared_ptr, and improves performance
by using atomic operations instead of mutex locking.

Note: this option changes the ABI of libstdc++ atomic/shared_ptr
helpers. It can be incompatible when linking against prebuilt
libraries that were compiled without it, leading to link errors or
undefined runtime behavior. Only enable it if all C++ objects and
libraries in the build use the same setting.
This commit is contained in:
Alexey Lapshin
2026-07-23 18:20:25 +07:00
parent 480d5f2559
commit b3ae652f21
16 changed files with 239 additions and 0 deletions
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docs/en/api-guides/performance/ram-usage.rst
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@@ -160,6 +160,7 @@ There are some ESP-IDF configuration options that can reduce heap usage at runti
:esp32: - In single-core mode only, it is possible to use IRAM as byte-accessible memory added to the regular heap by enabling :ref:`CONFIG_ESP32_IRAM_AS_8BIT_ACCESSIBLE_MEMORY`. Note that this option carries a performance penalty, and the risk of security issues caused by executable data. If this option is enabled, then it is possible to set other options to prefer certain buffers allocated from this memory: :ref:`CONFIG_MBEDTLS_MEM_ALLOC_MODE`, :ref:`NimBLE <CONFIG_BT_NIMBLE_MEM_ALLOC_MODE>`.
:esp32: - Reduce :ref:`CONFIG_BTDM_CTRL_BLE_MAX_CONN` if using Bluetooth LE.
:esp32: - Reduce :ref:`CONFIG_BTDM_CTRL_BR_EDR_MAX_ACL_CONN` if using Bluetooth Classic.
:CONFIG_IDF_TARGET_ARCH_RISCV and not esp32c2 and not esp32c3: - Enabling :ref:`CONFIG_COMPILER_CXX_ATOMIC_LOCK_POLICY` forces libstdc++ lock-free ``std::shared_ptr`` reference counting instead of a mutex-based implementation, avoiding an embedded mutex in each control block and saving about 88 bytes of heap per ``shared_ptr``. All C++ object files and linked libraries must use the same setting; see the config help for ABI details.
.. note::