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[router-table] simplify Allocate() and random selection of ID (#8032)

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This commit updates `RouterTable::Allocate()` to use Reservoir
sampling algorithm to randomly select a router ID while iterating
through the list of available IDs.
This commit is contained in:
Abtin Keshavarzian
2022-08-17 15:36:10 -07:00
committed by GitHub
parent 061d22ba8e
commit 1d10948069
1 changed files with 19 additions and 29 deletions
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src/core/thread/router_table.cpp
+19 -29
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@@ -205,9 +205,11 @@ void RouterTable::UpdateAllocation(void)
Router *RouterTable::Allocate(void)
{
Router *rval = nullptr;
uint8_t numAvailable = 0;
uint8_t freeBit;
Router *router = nullptr;
uint8_t numAvailable = 0;
uint8_t selectedRouterId = Mle::kInvalidRouterId;
VerifyOrExit(mActiveRouterCount < Mle::kMaxRouters);
// count available router ids
#if OPENTHREAD_CONFIG_REFERENCE_DEVICE_ENABLE
@@ -219,38 +221,26 @@ Router *RouterTable::Allocate(void)
if (!IsAllocated(routerId) && mRouterIdReuseDelay[routerId] == 0)
{
numAvailable++;
// Randomly select a router ID as we iterate through the
// list using Reservoir algorithm: We replace the
// selected ID with current entry in the list with
// probably `1/numAvailable`.
if (Random::NonCrypto::GetUint8InRange(0, numAvailable) == 0)
{
selectedRouterId = routerId;
}
}
}
VerifyOrExit(mActiveRouterCount < Mle::kMaxRouters && numAvailable > 0);
VerifyOrExit(selectedRouterId != Mle::kInvalidRouterId);
// choose available router id at random
freeBit = Random::NonCrypto::GetUint8InRange(0, numAvailable);
// allocate router
#if OPENTHREAD_CONFIG_REFERENCE_DEVICE_ENABLE
for (uint8_t routerId = mMinRouterId; routerId <= mMaxRouterId; routerId++)
#else
for (uint8_t routerId = 0; routerId <= Mle::kMaxRouterId; routerId++)
#endif
{
if (IsAllocated(routerId) || mRouterIdReuseDelay[routerId] > 0)
{
continue;
}
if (freeBit == 0)
{
rval = Allocate(routerId);
OT_ASSERT(rval != nullptr);
ExitNow();
}
freeBit--;
}
router = Allocate(selectedRouterId);
OT_ASSERT(router != nullptr);
exit:
return rval;
return router;
}
Router *RouterTable::Allocate(uint8_t aRouterId)