GCC Code Coverage Report

Directory: Os/Generic/Types/
File: AtomicQueue.cpp
Date: 2026-09-03 21:15:49
Exec Total Coverage
Lines: 155 169 91.7%
Functions: 13 14 92.9%
Branches: 53 71 74.6%
Line Branch Exec Source
1 // ======================================================================
2 // \title AtomicQueue.cpp
3 // \author B. Duckett
4 // \brief Lock-free MPMC circular buffer with embedded buffer storage
5 //
6 // \copyright
7 // Copyright 2026, by the California Institute of Technology.
8 // ALL RIGHTS RESERVED. United States Government Sponsorship
9 // acknowledged.
10 //
11 // ======================================================================
12
13 #include <Fw/Types/Assert.hpp>
14 #include <Os/Generic/Types/AtomicQueue.hpp>
15 #include <cstdio>
16 #include <cstring>
17 #include <new>
18
19 namespace Types {
20
21 ✗ U32 AtomicQueue::computeChecksum(const U8* buffer, FwSizeType size) {
22 ✗ FW_ASSERT(buffer != nullptr);
23 ✗ U32 sum = 0;
24 ✗ for (FwSizeType i = 0; i < size; ++i) {
25 ✗ sum += buffer[i];
26 ✗ sum = (sum << 1) | (sum >> 31); // Rotate left
27 }
28 ✗ return sum;
29 }
30
31 24 AtomicQueue::AtomicQueue()
32 24 : m_slots(nullptr),
33 24 m_bufferMemory(nullptr),
34 24 m_capacity(0),
35 24 m_bufferSize(0),
36 24 m_mask(0),
37 24 m_enqueuePos(0),
38 24 m_dequeuePos(0),
39 24 m_allocator(nullptr),
40 24 m_allocatorId(0),
41 24 m_notFullSem(nullptr) {}
42
43 24 AtomicQueue::~AtomicQueue() {
44 24 this->teardown();
45 24 }
46
47 20 void AtomicQueue::create(FwSizeType numBuffers,
48 FwSizeType bufferSize,
49 Fw::MemAllocator& allocator,
50 FwEnumStoreType allocatorId) {
51 20 FW_ASSERT(numBuffers > 0, static_cast<FwAssertArgType>(numBuffers));
52 20 FW_ASSERT(bufferSize > 0, static_cast<FwAssertArgType>(bufferSize));
53
54 20 this->m_capacity = numBuffers;
55 20 this->m_bufferSize = bufferSize;
56 20 this->m_allocator = &allocator;
57 20 this->m_allocatorId = allocatorId;
58
59 // Optimization: use bitwise AND for power-of-2, otherwise modulo
60 20 bool isPowerOf2 = (numBuffers & (numBuffers - 1)) == 0;
61
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 20 this->m_mask = isPowerOf2 ? (numBuffers - 1) : 0;
62
63 // Allocate slot array (with overflow check)
64 20 FW_ASSERT(numBuffers <= std::numeric_limits<FwSizeType>::max() / sizeof(Slot),
65 static_cast<FwAssertArgType>(numBuffers), static_cast<FwAssertArgType>(sizeof(Slot)));
66 20 FwSizeType slotsSize = numBuffers * sizeof(Slot);
67
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 20 void* slotMem = allocator.checkedAllocate(allocatorId, slotsSize, alignof(Slot));
68 20 FW_ASSERT(slotMem != nullptr, static_cast<FwAssertArgType>(numBuffers), static_cast<FwAssertArgType>(bufferSize));
69 20 this->m_slots = static_cast<Slot*>(slotMem);
70
71 // Allocate contiguous buffer memory for all slots (with overflow check)
72 20 FW_ASSERT(numBuffers <= std::numeric_limits<FwSizeType>::max() / bufferSize,
73 static_cast<FwAssertArgType>(numBuffers), static_cast<FwAssertArgType>(bufferSize));
74 20 FwSizeType totalBufferSize = numBuffers * bufferSize;
75
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 20 void* bufferMem = allocator.checkedAllocate(allocatorId, totalBufferSize, 64);
76 20 FW_ASSERT(bufferMem != nullptr, static_cast<FwAssertArgType>(numBuffers), static_cast<FwAssertArgType>(bufferSize));
77 20 this->m_bufferMemory = static_cast<U8*>(bufferMem);
78
79 // Initialize all slots with placement new and assign buffer pointers
80
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 343 for (FwSizeType i = 0; i < numBuffers; ++i) {
81 323 Slot* slot = new (&this->m_slots[i]) Slot();
82
83 // Assign buffer from contiguous memory block
84 323 slot->buffer = this->m_bufferMemory + (i * bufferSize);
85 323 slot->size = 0;
86 323 slot->sequence.store(i, std::memory_order_relaxed);
87
88 // Runtime verification that sequence atomics are lock-free
89 // This is critical for ISR safety and lock-free guarantee
90 323 FW_ASSERT(slot->sequence.is_lock_free(), static_cast<FwAssertArgType>(i),
91 static_cast<FwAssertArgType>(numBuffers));
92 }
93
94 // Create semaphore for blocking enqueue support (all platforms)
95 // Allocate semaphore using provided allocator
96 20 FwSizeType semSize = sizeof(Os::CountingSemaphore);
97
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 20 void* semMem = allocator.checkedAllocate(allocatorId, semSize, alignof(Os::CountingSemaphore));
98 20 FW_ASSERT(semMem != nullptr, static_cast<FwAssertArgType>(numBuffers));
99
100 // Use placement new to construct semaphore with initial count = numBuffers (all slots available)
101
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 20 this->m_notFullSem = new (semMem) Os::CountingSemaphore(static_cast<U32>(numBuffers));
102 20 FW_ASSERT(this->m_notFullSem != nullptr, static_cast<FwAssertArgType>(numBuffers));
103
104 20 this->m_enqueuePos.store(0, std::memory_order_relaxed);
105 20 this->m_dequeuePos.store(0, std::memory_order_relaxed);
106 20 }
107
108 49 void AtomicQueue::teardown() {
109 // Destroy and deallocate semaphore
110
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 49 if (this->m_notFullSem != nullptr) {
111 20 FW_ASSERT(this->m_allocator != nullptr, 0);
112
113 // Call destructor
114 20 this->m_notFullSem->~CountingSemaphore();
115
116 // Deallocate memory
117 20 this->m_allocator->deallocate(this->m_allocatorId, this->m_notFullSem);
118 20 this->m_notFullSem = nullptr;
119 }
120
121 // Destroy slots and deallocate memory
122
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 49 if (this->m_slots != nullptr) {
123 20 FW_ASSERT(this->m_capacity > 0, static_cast<FwAssertArgType>(this->m_capacity));
124 20 FW_ASSERT(this->m_allocator != nullptr, 0);
125
126 // Call destructors on slots
127
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 343 for (FwSizeType i = 0; i < this->m_capacity; ++i) {
128 323 FW_ASSERT(i < this->m_capacity, static_cast<FwAssertArgType>(i),
129 static_cast<FwAssertArgType>(this->m_capacity));
130 323 this->m_slots[i].~Slot();
131 }
132
133 // Deallocate buffer memory
134
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 20 if (this->m_bufferMemory != nullptr) {
135 20 this->m_allocator->deallocate(this->m_allocatorId, this->m_bufferMemory);
136 20 this->m_bufferMemory = nullptr;
137 }
138
139 // Deallocate slot array
140 20 this->m_allocator->deallocate(this->m_allocatorId, this->m_slots);
141 20 this->m_slots = nullptr;
142 }
143
144 49 this->m_enqueuePos.store(0, std::memory_order_relaxed);
145 49 this->m_dequeuePos.store(0, std::memory_order_relaxed);
146 49 this->m_capacity = 0;
147 49 this->m_bufferSize = 0;
148 49 this->m_mask = 0;
149 49 this->m_allocator = nullptr;
150 49 }
151
152 47637 bool AtomicQueue::enqueueInternal(const U8* buffer, FwSizeType size) {
153 47637 FW_ASSERT(this->m_slots != nullptr, 0);
154 47637 FW_ASSERT(buffer != nullptr, 0);
155 47637 FW_ASSERT(size > 0, static_cast<FwAssertArgType>(size));
156 47637 FW_ASSERT(size <= this->m_bufferSize, static_cast<FwAssertArgType>(size),
157 static_cast<FwAssertArgType>(this->m_bufferSize));
158
159
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 48020 for (FwSizeType retry = 0; retry < MAX_CAS_RETRIES; ++retry) {
160 48021 FW_ASSERT(retry < MAX_CAS_RETRIES, static_cast<FwAssertArgType>(retry));
161
162 // acquire-release on slot->sequence ensures coherence, enqueuePos & dequeuePos are relaxed since strong memory
163 // ordering is not required
164
165 // Get current enqueue position
166 48021 FwSizeType pos = this->m_enqueuePos.load(std::memory_order_relaxed);
167
168 // Check against dequeue position to prevent lapping (detect full queue)
169 48013 FwSizeType deqPos = this->m_dequeuePos.load(std::memory_order_relaxed);
170 48007 FwSignedSizeType queueDiff = static_cast<FwSignedSizeType>(pos) - static_cast<FwSignedSizeType>(deqPos);
171
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 48007 if (queueDiff >= static_cast<FwSignedSizeType>(this->m_capacity)) {
172 1740 return false; // Queue is full
173 }
174
175
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 46271 Slot* slot = &this->m_slots[this->getIndex(pos)];
176 46270 FwSizeType seq = slot->sequence.load(std::memory_order_acquire);
177
178 // Check if slot is ready for write (seq == pos means available)
179 46266 FwSignedSizeType diff = static_cast<FwSignedSizeType>(seq) - static_cast<FwSignedSizeType>(pos);
180
181
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 46266 if (diff == 0) {
182 // Slot available, try to claim it
183
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 92219 if (this->m_enqueuePos.compare_exchange_weak(pos, pos + 1, std::memory_order_release,
184 std::memory_order_relaxed)) {
185 // Claimed the slot, copy message data
186 45906 FW_ASSERT(slot->buffer != nullptr, static_cast<FwAssertArgType>(pos));
187
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 45906 (void)std::memcpy(slot->buffer, buffer, size);
188 45906 slot->size = size;
189
190 // Mark slot as ready for read
191 45904 slot->sequence.store(pos + 1, std::memory_order_release);
192 45904 return true;
193 }
194
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 157 } else if (diff < 0) {
195 // Queue is full (wrapped around)
196 1 return false;
197 }
198 // else: another producer claimed this slot, retry
199 }
200
201 ✗ return false;
202 }
203
204 47633 bool AtomicQueue::enqueue(const U8* buffer, FwSizeType size) {
205 47633 bool success = this->enqueueInternal(buffer, size);
206
207 // Decrement semaphore to track available slots (if semaphore exists)
208 // This ensures blocking sends see correct availability even when
209 // queue is filled via non-blocking sends.
210 //
211 // NOTE: tryWait() may fail due to race conditions when multiple threads
212 // concurrently enqueue. This is acceptable - the semaphore is a best-effort
213 // hint for blocking operations. The lock-free atomics in enqueueInternal()
214 // are the authoritative source of queue state.
215
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 47641 if (success && this->m_notFullSem != nullptr) {
216 45899 (void)this->m_notFullSem->tryWait();
217 }
218
219 47634 return success;
220 }
221
222 8 bool AtomicQueue::enqueueBlocking(const U8* buffer, FwSizeType size, bool blockIfFull) {
223 8 FW_ASSERT(this->m_slots != nullptr, 0);
224 8 FW_ASSERT(buffer != nullptr, 0);
225
226 // If not blocking or no semaphore, just use non-blocking enqueue
227
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 8 if (!blockIfFull || this->m_notFullSem == nullptr) {
228 5 return this->enqueue(buffer, size);
229 }
230
231 // Wait-first pattern: reserve slot via semaphore, then enqueue
232 // This prevents semaphore count drift under contention
233
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 3 for (FwSizeType attempt = 0; attempt < MAX_CAS_RETRIES; ++attempt) {
234 3 FW_ASSERT(attempt < MAX_CAS_RETRIES, static_cast<FwAssertArgType>(attempt));
235
236 // Reserve a slot by waiting on semaphore (blocks until space available)
237 3 Os::CountingSemaphoreInterface::Status status = this->m_notFullSem->wait();
238 3 FW_ASSERT(status == Os::CountingSemaphoreInterface::Status::OP_OK, static_cast<FwAssertArgType>(status));
239
240 // Try to enqueue (should succeed since we reserved a slot)
241 // Use internal method to avoid double-decrementing semaphore
242
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 3 if (this->enqueueInternal(buffer, size)) {
243 3 return true; // Success
244 }
245
246 // Extremely rare: slot was stolen between wait() and enqueue()
247 // Return the semaphore permit and retry
248 ✗ status = this->m_notFullSem->post();
249 ✗ FW_ASSERT(status == Os::CountingSemaphoreInterface::Status::OP_OK, static_cast<FwAssertArgType>(status));
250 }
251
252 // Exceeded retry limit (should never happen in practice)
253 ✗ return false;
254 }
255
256 46060 bool AtomicQueue::dequeue(U8* buffer, FwSizeType capacity, FwSizeType& actualSize) {
257 46060 FW_ASSERT(this->m_slots != nullptr, 0);
258 46059 FW_ASSERT(buffer != nullptr, 0);
259 46059 FW_ASSERT(capacity > 0, static_cast<FwAssertArgType>(capacity));
260
261
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 46595 for (FwSizeType retry = 0; retry < MAX_CAS_RETRIES; ++retry) {
262 46593 FW_ASSERT(retry < MAX_CAS_RETRIES, static_cast<FwAssertArgType>(retry));
263
264 // acquire-release on slot->sequence ensures coherence, enqueuePos & dequeuePos are relaxed since strong memory
265 // ordering is not required
266
267 // Get current dequeue & enqueue positions
268 46593 FwSizeType pos = this->m_dequeuePos.load(std::memory_order_relaxed);
269
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 46571 Slot* slot = &this->m_slots[this->getIndex(pos)];
270 46510 FwSizeType seq = slot->sequence.load(std::memory_order_acquire);
271
272 // Check if slot is ready for read (seq == pos + 1 means data available)
273 46517 FwSignedSizeType diff = static_cast<FwSignedSizeType>(seq) - static_cast<FwSignedSizeType>(pos + 1);
274
275
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 46517 if (diff == 0) {
276 // Slot has data, try to claim it
277
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 92724 if (this->m_dequeuePos.compare_exchange_weak(pos, pos + 1, std::memory_order_release,
278 std::memory_order_relaxed)) {
279 // Claimed the slot, check size and copy data
280 // Note: sequence.load(acquire) at 10 lines above already synchronizes with
281 // enqueue's sequence.store(release), ensuring size & buffer coherency
282 45895 FW_ASSERT(slot->buffer != nullptr, static_cast<FwAssertArgType>(pos));
283 45895 FW_ASSERT(slot->size > 0, static_cast<FwAssertArgType>(slot->size));
284 45895 FW_ASSERT(slot->size <= capacity, static_cast<FwAssertArgType>(slot->size),
285 static_cast<FwAssertArgType>(capacity));
286
287 45895 actualSize = slot->size;
288
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 45895 (void)std::memcpy(buffer, slot->buffer, actualSize);
289
290 // Mark slot as available for next cycle (pos + capacity)
291 45895 slot->sequence.store(pos + this->m_capacity, std::memory_order_release);
292
293 // Post semaphore to wake up blocked enqueue threads (if semaphore exists)
294 // ISR-SAFETY NOTE: Calling from ISR depends on platform semaphore implementation.
295 // See header comments for details.
296
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 45894 if (this->m_notFullSem != nullptr) {
297
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 45894 Os::CountingSemaphoreInterface::Status status = this->m_notFullSem->post();
298 45887 FW_ASSERT(status == Os::CountingSemaphoreInterface::Status::OP_OK,
299 static_cast<FwAssertArgType>(status));
300 }
301
302 45886 return true;
303 }
304
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 149 } else if (diff < 0) {
305 // Queue is empty (no data written yet)
306 167 return false;
307 }
308 // else: another consumer claimed this slot, retry
309 }
310
311 2 return false;
312 }
313
314 7 bool AtomicQueue::isFull() const {
315 // Queue is full if enqueue is exactly capacity ahead of dequeue
316 // Return false for uninitialized queue
317
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 7 if (this->m_capacity == 0) {
318 ✗ return false;
319 }
320 7 return this->getSize() >= this->m_capacity;
321 }
322
323 12 bool AtomicQueue::isEmpty() const {
324 12 return this->getSize() == 0;
325 }
326
327 28 FwSizeType AtomicQueue::getSize() const {
328 // Safe to call on uninitialized queue
329
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 28 if (this->m_capacity == 0) {
330 1 return 0;
331 }
332 // A nonzero capacity implies the queue was created with backing storage
333 26 FW_ASSERT(this->m_slots != nullptr);
334
335 27 FwSizeType enq = this->m_enqueuePos.load(std::memory_order_relaxed);
336 27 FwSizeType deq = this->m_dequeuePos.load(std::memory_order_relaxed);
337 26 FwSignedSizeType diff = static_cast<FwSignedSizeType>(enq) - static_cast<FwSignedSizeType>(deq);
338
339 // Two independent relaxed loads provide no cross-variable consistency guarantee.
340 // Restrict to [0, capacity] rather than asserting — diff can be transiently negative
341 // or > capacity on concurrent access even though no real program state has that.
342
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 26 if (diff < 0) {
343 ✗ return 0;
344 }
345
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 26 if (static_cast<FwSizeType>(diff) > this->m_capacity) {
346 ✗ return this->m_capacity;
347 }
348 26 return static_cast<FwSizeType>(diff);
349 }
350
351 4 FwSizeType AtomicQueue::getCapacity() const {
352 // Safe to call on uninitialized queue - returns 0 if not created
353 4 return this->m_capacity;
354 }
355
356 4 FwSizeType AtomicQueue::getBufferSize() const {
357 // Safe to call on uninitialized queue - returns 0 if not created
358 4 return this->m_bufferSize;
359 }
360
361 } // namespace Types
362