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fix underflow

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This commit is contained in:
J. Nick Koston
2025-09-28 18:41:20 -05:00
parent e07af13bef
commit d65b1fad67
1 changed files with 23 additions and 17 deletions
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40
esphome/components/usb_host/usb_host_client.cpp
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@@ -361,24 +361,30 @@ TransferRequest *USBClient::get_trq_() {
uint16_t mask = this->trq_in_use_.load(std::memory_order_relaxed);
// Find first available slot (bit = 0) and try to claim it atomically
for (size_t i = 0; i < MAX_REQUESTS; i++) {
if (!(mask & (1U << i))) {
// Slot i appears available, try to claim it atomically
uint16_t expected = mask;
uint16_t desired = mask | (1U << i); // Set bit i to mark as in-use
if (this->trq_in_use_.compare_exchange_weak(expected, desired, std::memory_order_acquire,
std::memory_order_relaxed)) {
// Successfully claimed slot i - prepare the TransferRequest
auto *trq = &this->requests_[i];
trq->transfer->context = trq;
trq->transfer->device_handle = this->device_handle_;
return trq;
}
// Another thread claimed this slot, retry with updated mask
mask = expected;
i--; // Retry the same index with new mask value
// We use a while loop to allow retrying the same slot after CAS failure
size_t i = 0;
while (i < MAX_REQUESTS) {
if (mask & (1U << i)) {
// Slot is in use, move to next slot
i++;
continue;
}
// Slot i appears available, try to claim it atomically
uint16_t expected = mask;
uint16_t desired = mask | (1U << i); // Set bit i to mark as in-use
if (this->trq_in_use_.compare_exchange_weak(expected, desired, std::memory_order_acquire,
std::memory_order_relaxed)) {
// Successfully claimed slot i - prepare the TransferRequest
auto *trq = &this->requests_[i];
trq->transfer->context = trq;
trq->transfer->device_handle = this->device_handle_;
return trq;
}
// Another thread claimed this slot, retry with updated mask
// Don't increment i - retry the same slot with the updated mask
mask = expected;
}
ESP_LOGE(TAG, "Too many requests queued (all %d slots in use)", MAX_REQUESTS);