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gh-141498: Change backoff counter to use powers of 4 instead of powers of 2 #141589

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efimov-mikhail wants to merge 2 commits into from
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gh-141498: Change backoff counter to use powers of 4 instead of powers of 2 #141589

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86de63a
Some refactor
efimov-mikhail Nov 15, 2025
4eb3231
Changes in backoff bit pattern
efimov-mikhail Nov 15, 2025
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Some refactor
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@efimov-mikhail
efimov-mikhail committed Nov 15, 2025
commit 86de63aa1f8cdc53550d750547c12c11cb181bc8
8 changes: 5 additions & 3 deletions Include/internal/pycore_backoff.h
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Original file line number Diff line number Diff line change
Expand Up @@ -32,8 +32,10 @@ extern "C" {
*/

#define BACKOFF_BITS 4
#define BACKOFF_MASK 0xF
#define MAX_BACKOFF 12
#define UNREACHABLE_BACKOFF 15
#define MAX_VALUE 0xFFF

static inline bool
is_unreachable_backoff_counter(_Py_BackoffCounter counter)
Expand All @@ -44,8 +46,8 @@ is_unreachable_backoff_counter(_Py_BackoffCounter counter)
static inline _Py_BackoffCounter
make_backoff_counter(uint16_t value, uint16_t backoff)
{
assert(backoff <= 15);
assert(value <= 0xFFF);
assert(backoff <= UNREACHABLE_BACKOFF);
assert(value <= MAX_VALUE);
_Py_BackoffCounter result;
result.value_and_backoff = (value << BACKOFF_BITS) | backoff;
return result;
Expand All @@ -63,7 +65,7 @@ static inline _Py_BackoffCounter
restart_backoff_counter(_Py_BackoffCounter counter)
{
assert(!is_unreachable_backoff_counter(counter));
int backoff = counter.value_and_backoff & 15;
int backoff = counter.value_and_backoff & BACKOFF_MASK;
if (backoff < MAX_BACKOFF) {
return make_backoff_counter((1 << (backoff + 1)) - 1, backoff + 1);
}
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