py/modsys: Add sys.implementation._thread attribute.

This is useful to distinguish between GIL and non-GIL builds.

Signed-off-by: Damien George <damien@micropython.org>

docs/library/sys.rst

@@ -77,6 +77,8 @@ Constants
    * *_mpy* - supported mpy file-format version (optional attribute)
    * *_build* - string that can help identify the configuration that
      MicroPython was built with
+   * *_thread* - optional string attribute, exists if the target has threading
+     and is either "GIL" or "unsafe"
 
    This object is the recommended way to distinguish MicroPython from other
    Python implementations (note that it still may not exist in the very
@@ -95,6 +97,14 @@ Constants
    * On microcontroller targets, the first element is the board name and the second
      element (if present) is the board variant, for example ``'RPI_PICO2-RISCV'``
 
+   The *_thread* entry was added in version 1.26.0 and if it exists then the
+   target has the ``_thread`` module.  If the target enables the GIL (global
+   interpreter lock) then this attribute is ``"GIL"``.  Otherwise the attribute
+   is ``"unsafe"`` and the target has threading but does not enable the GIL,
+   and mutable Python objects (such as `bytearray`, `list` and `dict`) that are
+   shared amongst threads must be protected explicitly by locks such as
+   ``_thread.allocate_lock``.
+
    .. admonition:: Difference to CPython
       :class: attention
 

py/modsys.c

@@ -103,6 +103,18 @@ static const MP_DEFINE_STR_OBJ(mp_sys_implementation__build_obj, MICROPY_BOARD_B
 #define SYS_IMPLEMENTATION_ELEMS__BUILD
 #endif
 
+#if MICROPY_PY_THREAD
+#if MICROPY_PY_THREAD_GIL
+#define SYS_IMPLEMENTATION_ELEMS__THREAD \
+    , MP_ROM_QSTR(MP_QSTR_GIL)
+#else
+#define SYS_IMPLEMENTATION_ELEMS__THREAD \
+    , MP_ROM_QSTR(MP_QSTR_unsafe)
+#endif
+#else
+#define SYS_IMPLEMENTATION_ELEMS__THREAD
+#endif
+
 #if MICROPY_PREVIEW_VERSION_2
 #define SYS_IMPLEMENTATION_ELEMS__V2 \
     , MP_ROM_TRUE
@@ -120,6 +132,9 @@ static const qstr impl_fields[] = {
     #if defined(MICROPY_BOARD_BUILD_NAME)
     MP_QSTR__build,
     #endif
+    #if MICROPY_PY_THREAD
+    MP_QSTR__thread,
+    #endif
     #if MICROPY_PREVIEW_VERSION_2
     MP_QSTR__v2,
     #endif
@@ -127,20 +142,21 @@ static const qstr impl_fields[] = {
 static MP_DEFINE_ATTRTUPLE(
     mp_sys_implementation_obj,
     impl_fields,
-    3 + MICROPY_PERSISTENT_CODE_LOAD + MICROPY_BOARD_BUILD + MICROPY_PREVIEW_VERSION_2,
+    3 + MICROPY_PERSISTENT_CODE_LOAD + MICROPY_BOARD_BUILD + MICROPY_PY_THREAD + MICROPY_PREVIEW_VERSION_2,
     SYS_IMPLEMENTATION_ELEMS_BASE
     SYS_IMPLEMENTATION_ELEMS__MPY
     SYS_IMPLEMENTATION_ELEMS__BUILD
+    SYS_IMPLEMENTATION_ELEMS__THREAD
     SYS_IMPLEMENTATION_ELEMS__V2
     );
 #else
 static const mp_rom_obj_tuple_t mp_sys_implementation_obj = {
     {&mp_type_tuple},
     3 + MICROPY_PERSISTENT_CODE_LOAD,
-    // Do not include SYS_IMPLEMENTATION_ELEMS__BUILD or SYS_IMPLEMENTATION_ELEMS__V2
+    // Do not include SYS_IMPLEMENTATION_ELEMS__BUILD, SYS_IMPLEMENTATION_ELEMS__THREAD
-    // because SYS_IMPLEMENTATION_ELEMS__MPY may be empty if
+    // or SYS_IMPLEMENTATION_ELEMS__V2 because SYS_IMPLEMENTATION_ELEMS__MPY may be empty if
     // MICROPY_PERSISTENT_CODE_LOAD is disabled, which means they'll share
-    // the same index. Cannot query _build or _v2 if MICROPY_PY_ATTRTUPLE is
+    // the same index. Cannot query _build, _thread or _v2 if MICROPY_PY_ATTRTUPLE is
     // disabled.
     {
         SYS_IMPLEMENTATION_ELEMS_BASE

tests/basics/sys1.py

@@ -30,6 +30,12 @@ else:
     # Effectively skip subtests
     print(str)
 
+if hasattr(sys.implementation, '_thread'):
+    print(sys.implementation._thread in ("GIL", "unsafe"))
+else:
+    # Effectively skip subtests
+    print(True)
+
 try:
     print(sys.intern('micropython') == 'micropython')
     has_intern = True