--- /dev/null
+/*
+ * Copyright 2014 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FOLLY_LIFOSEM_H
+#define FOLLY_LIFOSEM_H
+
+#include <string.h>
+#include <stdint.h>
+#include <atomic>
+#include <algorithm>
+#include <memory>
+#include <system_error>
+
+#include "folly/AtomicStruct.h"
+#include "folly/Baton.h"
+#include "folly/IndexedMemPool.h"
+#include "folly/Likely.h"
+#include "folly/detail/CacheLocality.h"
+
+namespace folly {
+
+template <template<typename> class Atom = std::atomic,
+ class BatonType = Baton<Atom>>
+struct LifoSemImpl;
+
+/// LifoSem is a semaphore that wakes its waiters in a manner intended to
+/// maximize performance rather than fairness. It should be preferred
+/// to a mutex+condvar or POSIX sem_t solution when all of the waiters
+/// are equivalent. It is faster than a condvar or sem_t, and it has a
+/// shutdown state that might save you a lot of complexity when it comes
+/// time to shut down your work pipelines. LifoSem is larger than sem_t,
+/// but that is only because it uses padding and alignment to avoid
+/// false sharing.
+///
+/// LifoSem allows multi-post and multi-tryWait, and provides a shutdown
+/// state that awakens all waiters. LifoSem is faster than sem_t because
+/// it performs exact wakeups, so it often requires fewer system calls.
+/// It provides all of the functionality of sem_t except for timed waiting.
+/// It is called LifoSem because its wakeup policy is approximately LIFO,
+/// rather than the usual FIFO.
+///
+/// The core semaphore operations provided are:
+///
+/// -- post() -- if there is a pending waiter, wake it up, otherwise
+/// increment the value of the semaphore. If the value of the semaphore
+/// is already 2^32-1, does nothing. Compare to sem_post().
+///
+/// -- post(n) -- equivalent to n calls to post(), but much more efficient.
+/// sem_t has no equivalent to this method.
+///
+/// -- bool tryWait() -- if the semaphore's value is positive, decrements it
+/// and returns true, otherwise returns false. Compare to sem_trywait().
+///
+/// -- uint32_t tryWait(uint32_t n) -- attempts to decrement the semaphore's
+/// value by n, returning the amount by which it actually was decremented
+/// (a value from 0 to n inclusive). Not atomic. Equivalent to n calls
+/// to tryWait(). sem_t has no equivalent to this method.
+///
+/// -- wait() -- waits until tryWait() can succeed. Compare to sem_wait().
+///
+/// LifoSem also has the notion of a shutdown state, in which any calls
+/// that would block (or are already blocked) throw ShutdownSemError.
+/// Note the difference between a call to wait() and a call to wait()
+/// that might block. In the former case tryWait() would succeed, and no
+/// isShutdown() check is performed. In the latter case an exception is
+/// thrown. This behavior allows a LifoSem controlling work distribution
+/// to drain. If you want to immediately stop all waiting on shutdown,
+/// you can just check isShutdown() yourself (preferrably wrapped in
+/// an UNLIKELY). This fast-stop behavior is easy to add, but difficult
+/// to remove if you want the draining behavior, which is why we have
+/// chosen the former. Since wait() is the only method that can block,
+/// it is the only one that is affected by the shutdown state.
+///
+/// All LifoSem operations operations except valueGuess() are guaranteed
+/// to be linearizable.
+typedef LifoSemImpl<> LifoSem;
+
+
+/// The exception thrown when wait()ing on an isShutdown() LifoSem
+struct ShutdownSemError : public std::runtime_error {
+ explicit ShutdownSemError(const std::string& msg);
+ virtual ~ShutdownSemError() noexcept;
+};
+
+namespace detail {
+
+// Internally, a LifoSem is either a value or a linked list of wait nodes.
+// This union is captured in the LifoSemHead type, which holds either a
+// value or an indexed pointer to the list. LifoSemHead itself is a value
+// type, the head is a mutable atomic box containing a LifoSemHead value.
+// Each wait node corresponds to exactly one waiter. Values can flow
+// through the semaphore either by going into and out of the head's value,
+// or by direct communication from a poster to a waiter. The former path
+// is taken when there are no pending waiters, the latter otherwise. The
+// general flow of a post is to try to increment the value or pop-and-post
+// a wait node. Either of those have the effect of conveying one semaphore
+// unit. Waiting is the opposite, either a decrement of the value or
+// push-and-wait of a wait node. The generic LifoSemBase abstracts the
+// actual mechanism by which a wait node's post->wait communication is
+// performed, which is why we have LifoSemRawNode and LifoSemNode.
+
+/// LifoSemRawNode is the actual pooled storage that backs LifoSemNode
+/// for user-specified Handoff types. This is done so that we can have
+/// a large static IndexedMemPool of nodes, instead of per-type pools
+template <template<typename> class Atom>
+struct LifoSemRawNode {
+ std::aligned_storage<sizeof(void*),alignof(void*)>::type raw;
+
+ /// The IndexedMemPool index of the next node in this chain, or 0
+ /// if none. This will be set to uint32_t(-1) if the node is being
+ /// posted due to a shutdown-induced wakeup
+ uint32_t next;
+
+ bool isShutdownNotice() const { return next == uint32_t(-1); }
+ void clearShutdownNotice() { next = 0; }
+ void setShutdownNotice() { next = uint32_t(-1); }
+
+ typedef folly::IndexedMemPool<LifoSemRawNode<Atom>,32,200,Atom> Pool;
+
+ /// Storage for all of the waiter nodes for LifoSem-s that use Atom
+ static Pool pool;
+};
+
+/// Use this macro to declare the static storage that backs the raw nodes
+/// for the specified atomic type
+#define LIFOSEM_DECLARE_POOL(Atom, capacity) \
+ template<> \
+ folly::detail::LifoSemRawNode<Atom>::Pool \
+ folly::detail::LifoSemRawNode<Atom>::pool((capacity));
+
+/// Handoff is a type not bigger than a void* that knows how to perform a
+/// single post() -> wait() communication. It must have a post() method.
+/// If it has a wait() method then LifoSemBase's wait() implementation
+/// will work out of the box, otherwise you will need to specialize
+/// LifoSemBase::wait accordingly.
+template <typename Handoff, template<typename> class Atom>
+struct LifoSemNode : public LifoSemRawNode<Atom> {
+
+ static_assert(sizeof(Handoff) <= sizeof(LifoSemRawNode<Atom>::raw),
+ "Handoff too big for small-object optimization, use indirection");
+ static_assert(alignof(Handoff) <=
+ alignof(decltype(LifoSemRawNode<Atom>::raw)),
+ "Handoff alignment constraint not satisfied");
+
+ template <typename ...Args>
+ void init(Args&&... args) {
+ new (&this->raw) Handoff(std::forward<Args>(args)...);
+ }
+
+ void destroy() {
+ handoff().~Handoff();
+#ifndef NDEBUG
+ memset(&this->raw, 'F', sizeof(this->raw));
+#endif
+ }
+
+ Handoff& handoff() {
+ return *static_cast<Handoff*>(static_cast<void*>(&this->raw));
+ }
+
+ const Handoff& handoff() const {
+ return *static_cast<const Handoff*>(static_cast<const void*>(&this->raw));
+ }
+};
+
+template <typename Handoff, template<typename> class Atom>
+struct LifoSemNodeRecycler {
+ void operator()(LifoSemNode<Handoff,Atom>* elem) const {
+ elem->destroy();
+ auto idx = LifoSemRawNode<Atom>::pool.locateElem(elem);
+ LifoSemRawNode<Atom>::pool.recycleIndex(idx);
+ }
+};
+
+/// LifoSemHead is a 64-bit struct that holds a 32-bit value, some state
+/// bits, and a sequence number used to avoid ABA problems in the lock-free
+/// management of the LifoSem's wait lists. The value can either hold
+/// an integral semaphore value (if there are no waiters) or a node index
+/// (see IndexedMemPool) for the head of a list of wait nodes
+class LifoSemHead {
+ // What we really want are bitfields:
+ // uint64_t data : 32; uint64_t isNodeIdx : 1; uint64_t seq : 31;
+ // Unfortunately g++ generates pretty bad code for this sometimes (I saw
+ // -O3 code from gcc 4.7.1 copying the bitfields one at a time instead of
+ // in bulk, for example). We can generate better code anyway by assuming
+ // that setters won't be given values that cause under/overflow, and
+ // putting the sequence at the end where its planned overflow doesn't
+ // need any masking.
+ //
+ // data == 0 (empty list) with isNodeIdx is conceptually the same
+ // as data == 0 (no unclaimed increments) with !isNodeIdx, we always
+ // convert the former into the latter to make the logic simpler.
+ enum {
+ IsNodeIdxShift = 32,
+ IsShutdownShift = 33,
+ SeqShift = 34,
+ };
+ enum : uint64_t {
+ IsNodeIdxMask = uint64_t(1) << IsNodeIdxShift,
+ IsShutdownMask = uint64_t(1) << IsShutdownShift,
+ SeqIncr = uint64_t(1) << SeqShift,
+ SeqMask = ~(SeqIncr - 1),
+ };
+
+ public:
+
+ uint64_t bits;
+
+ //////// getters
+
+ inline uint32_t idx() const {
+ assert(isNodeIdx());
+ assert(uint32_t(bits) != 0);
+ return uint32_t(bits);
+ }
+ inline uint32_t value() const {
+ assert(!isNodeIdx());
+ return uint32_t(bits);
+ }
+ inline constexpr bool isNodeIdx() const {
+ return (bits & IsNodeIdxMask) != 0;
+ }
+ inline constexpr bool isShutdown() const {
+ return (bits & IsShutdownMask) != 0;
+ }
+ inline constexpr uint32_t seq() const {
+ return uint32_t(bits >> SeqShift);
+ }
+
+ //////// setter-like things return a new struct
+
+ /// This should only be used for initial construction, not for setting
+ /// the value, because it clears the sequence number
+ static inline constexpr LifoSemHead fresh(uint32_t value) {
+ return LifoSemHead{ value };
+ }
+
+ /// Returns the LifoSemHead that results from popping a waiter node,
+ /// given the current waiter node's next ptr
+ inline LifoSemHead withPop(uint32_t idxNext) const {
+ assert(isNodeIdx());
+ if (idxNext == 0) {
+ // no isNodeIdx bit or data bits. Wraparound of seq bits is okay
+ return LifoSemHead{ (bits & (SeqMask | IsShutdownMask)) + SeqIncr };
+ } else {
+ // preserve sequence bits (incremented with wraparound okay) and
+ // isNodeIdx bit, replace all data bits
+ return LifoSemHead{
+ (bits & (SeqMask | IsShutdownMask | IsNodeIdxMask)) +
+ SeqIncr + idxNext };
+ }
+ }
+
+ /// Returns the LifoSemHead that results from pushing a new waiter node
+ inline LifoSemHead withPush(uint32_t idx) const {
+ assert(isNodeIdx() || value() == 0);
+ assert(!isShutdown());
+ assert(idx != 0);
+ return LifoSemHead{ (bits & SeqMask) | IsNodeIdxMask | idx };
+ }
+
+ /// Returns the LifoSemHead with value increased by delta, with
+ /// saturation if the maximum value is reached
+ inline LifoSemHead withValueIncr(uint32_t delta) const {
+ assert(!isNodeIdx());
+ auto rv = LifoSemHead{ bits + SeqIncr + delta };
+ if (UNLIKELY(rv.isNodeIdx())) {
+ // value has overflowed into the isNodeIdx bit
+ rv = LifoSemHead{ (rv.bits & ~IsNodeIdxMask) | (IsNodeIdxMask - 1) };
+ }
+ return rv;
+ }
+
+ /// Returns the LifoSemHead that results from decrementing the value
+ inline LifoSemHead withValueDecr(uint32_t delta) const {
+ assert(delta > 0 && delta <= value());
+ return LifoSemHead{ bits + SeqIncr - delta };
+ }
+
+ /// Returns the LifoSemHead with the same state as the current node,
+ /// but with the shutdown bit set
+ inline LifoSemHead withShutdown() const {
+ return LifoSemHead{ bits | IsShutdownMask };
+ }
+
+ inline constexpr bool operator== (const LifoSemHead& rhs) const {
+ return bits == rhs.bits;
+ }
+ inline constexpr bool operator!= (const LifoSemHead& rhs) const {
+ return !(*this == rhs);
+ }
+};
+
+/// LifoSemBase is the engine for several different types of LIFO
+/// semaphore. LifoSemBase handles storage of positive semaphore values
+/// and wait nodes, but the actual waiting and notification mechanism is
+/// up to the client.
+///
+/// The Handoff type is responsible for arranging one wakeup notification.
+/// See LifoSemNode for more information on how to make your own.
+template <typename Handoff,
+ template<typename> class Atom = std::atomic>
+struct LifoSemBase : boost::noncopyable {
+
+ /// Constructor
+ explicit LifoSemBase(uint32_t initialValue = 0)
+ : head_(LifoSemHead::fresh(initialValue)) {}
+
+ /// Silently saturates if value is already 2^32-1
+ void post() {
+ auto idx = incrOrPop(1);
+ if (idx != 0) {
+ idxToNode(idx).handoff().post();
+ }
+ }
+
+ /// Equivalent to n calls to post(), except may be much more efficient.
+ /// At any point in time at which the semaphore's value would exceed
+ /// 2^32-1 if tracked with infinite precision, it may be silently
+ /// truncated to 2^32-1. This saturation is not guaranteed to be exact,
+ /// although it is guaranteed that overflow won't result in wrap-around.
+ /// There would be a substantial performance and complexity cost in
+ /// guaranteeing exact saturation (similar to the cost of maintaining
+ /// linearizability near the zero value, but without as much of
+ /// a benefit).
+ void post(uint32_t n) {
+ uint32_t idx;
+ while (n > 0 && (idx = incrOrPop(n)) != 0) {
+ // pop accounts for only 1
+ idxToNode(idx).handoff().post();
+ --n;
+ }
+ }
+
+ /// Returns true iff shutdown() has been called
+ bool isShutdown() const {
+ return UNLIKELY(head_.load(std::memory_order_acquire).isShutdown());
+ }
+
+ /// Prevents blocking on this semaphore, causing all blocking wait()
+ /// calls to throw ShutdownSemError. Both currently blocked wait() and
+ /// future calls to wait() for which tryWait() would return false will
+ /// cause an exception. Calls to wait() for which the matching post()
+ /// has already occurred will proceed normally.
+ void shutdown() {
+ // first set the shutdown bit
+ auto h = head_.load(std::memory_order_acquire);
+ while (!h.isShutdown()) {
+ if (head_.compare_exchange_strong(h, h.withShutdown())) {
+ // success
+ h = h.withShutdown();
+ break;
+ }
+ // compare_exchange_strong rereads h, retry
+ }
+
+ // now wake up any waiters
+ while (h.isNodeIdx()) {
+ auto& node = idxToNode(h.idx());
+ auto repl = h.withPop(node.next);
+ if (head_.compare_exchange_strong(h, repl)) {
+ // successful pop, wake up the waiter and move on. The next
+ // field is used to convey that this wakeup didn't consume a value
+ node.setShutdownNotice();
+ node.handoff().post();
+ h = repl;
+ }
+ }
+ }
+
+ /// Returns true iff value was decremented
+ bool tryWait() {
+ uint32_t n = 1;
+ auto rv = decrOrPush(n, 0);
+ assert((rv == WaitResult::DECR && n == 0) ||
+ (rv != WaitResult::DECR && n == 1));
+ // SHUTDOWN is okay here, since we don't actually wait
+ return rv == WaitResult::DECR;
+ }
+
+ /// Equivalent to (but may be much more efficient than) n calls to
+ /// tryWait(). Returns the total amount by which the semaphore's value
+ /// was decreased
+ uint32_t tryWait(uint32_t n) {
+ auto const orig = n;
+ while (n > 0) {
+#ifndef NDEBUG
+ auto prev = n;
+#endif
+ auto rv = decrOrPush(n, 0);
+ assert((rv == WaitResult::DECR && n < prev) ||
+ (rv != WaitResult::DECR && n == prev));
+ if (rv != WaitResult::DECR) {
+ break;
+ }
+ }
+ return orig - n;
+ }
+
+ /// Blocks the current thread until there is a matching post or the
+ /// semaphore is shut down. Throws ShutdownSemError if the semaphore
+ /// has been shut down and this method would otherwise be blocking.
+ /// Note that wait() doesn't throw during shutdown if tryWait() would
+ /// return true
+ void wait() {
+ // early check isn't required for correctness, but is an important
+ // perf win if we can avoid allocating and deallocating a node
+ if (tryWait()) {
+ return;
+ }
+
+ // allocateNode() won't compile unless Handoff has a default
+ // constructor
+ UniquePtr node = allocateNode();
+
+ auto rv = tryWaitOrPush(*node);
+ if (UNLIKELY(rv == WaitResult::SHUTDOWN)) {
+ assert(isShutdown());
+ throw ShutdownSemError("wait() would block but semaphore is shut down");
+ }
+
+ if (rv == WaitResult::PUSH) {
+ node->handoff().wait();
+ if (UNLIKELY(node->isShutdownNotice())) {
+ // this wait() didn't consume a value, it was triggered by shutdown
+ assert(isShutdown());
+ throw ShutdownSemError(
+ "blocking wait() interrupted by semaphore shutdown");
+ }
+
+ // node->handoff().wait() can't return until after the node has
+ // been popped and post()ed, so it is okay for the UniquePtr to
+ // recycle the node now
+ }
+ // else node wasn't pushed, so it is safe to recycle
+ }
+
+ /// Returns a guess at the current value, designed for debugging.
+ /// If there are no concurrent posters or waiters then this will
+ /// be correct
+ uint32_t valueGuess() const {
+ // this is actually linearizable, but we don't promise that because
+ // we may want to add striping in the future to help under heavy
+ // contention
+ auto h = head_.load(std::memory_order_acquire);
+ return h.isNodeIdx() ? 0 : h.value();
+ }
+
+ protected:
+
+ enum class WaitResult {
+ PUSH,
+ DECR,
+ SHUTDOWN,
+ };
+
+ /// The type of a std::unique_ptr that will automatically return a
+ /// LifoSemNode to the appropriate IndexedMemPool
+ typedef std::unique_ptr<LifoSemNode<Handoff, Atom>,
+ LifoSemNodeRecycler<Handoff, Atom>> UniquePtr;
+
+ /// Returns a node that can be passed to decrOrLink
+ template <typename... Args>
+ UniquePtr allocateNode(Args&&... args) {
+ auto idx = LifoSemRawNode<Atom>::pool.allocIndex();
+ if (idx != 0) {
+ auto& node = idxToNode(idx);
+ node.clearShutdownNotice();
+ try {
+ node.init(std::forward<Args>(args)...);
+ } catch (...) {
+ LifoSemRawNode<Atom>::pool.recycleIndex(idx);
+ throw;
+ }
+ return UniquePtr(&node);
+ } else {
+ return UniquePtr();
+ }
+ }
+
+ /// Returns DECR if the semaphore value was decremented (and waiterNode
+ /// was untouched), PUSH if a reference to the wait node was pushed,
+ /// or SHUTDOWN if decrement was not possible and push wasn't allowed
+ /// because isShutdown(). Ownership of the wait node remains the
+ /// responsibility of the caller, who must not release it until after
+ /// the node's Handoff has been posted.
+ WaitResult tryWaitOrPush(LifoSemNode<Handoff, Atom>& waiterNode) {
+ uint32_t n = 1;
+ return decrOrPush(n, nodeToIdx(waiterNode));
+ }
+
+ private:
+
+ folly::AtomicStruct<LifoSemHead,Atom> head_
+ FOLLY_ALIGN_TO_AVOID_FALSE_SHARING;
+
+ char padding_[folly::detail::CacheLocality::kFalseSharingRange -
+ sizeof(LifoSemHead)];
+
+
+ static LifoSemNode<Handoff, Atom>& idxToNode(uint32_t idx) {
+ auto raw = &LifoSemRawNode<Atom>::pool[idx];
+ return *static_cast<LifoSemNode<Handoff, Atom>*>(raw);
+ }
+
+ static uint32_t nodeToIdx(const LifoSemNode<Handoff, Atom>& node) {
+ return LifoSemRawNode<Atom>::pool.locateElem(&node);
+ }
+
+ /// Either increments by n and returns 0, or pops a node and returns it.
+ /// If n + the stripe's value overflows, then the stripe's value
+ /// saturates silently at 2^32-1
+ uint32_t incrOrPop(uint32_t n) {
+ while (true) {
+ assert(n > 0);
+
+ auto head = head_.load(std::memory_order_acquire);
+ if (head.isNodeIdx()) {
+ auto& node = idxToNode(head.idx());
+ if (head_.compare_exchange_strong(head, head.withPop(node.next))) {
+ // successful pop
+ return head.idx();
+ }
+ } else {
+ auto after = head.withValueIncr(n);
+ if (head_.compare_exchange_strong(head, after)) {
+ // successful incr
+ return 0;
+ }
+ }
+ // retry
+ }
+ }
+
+ /// Returns DECR if some amount was decremented, with that amount
+ /// subtracted from n. If n is 1 and this function returns DECR then n
+ /// must be 0 afterward. Returns PUSH if no value could be decremented
+ /// and idx was pushed, or if idx was zero and no push was performed but
+ /// a push would have been performed with a valid node. Returns SHUTDOWN
+ /// if the caller should have blocked but isShutdown(). If idx == 0,
+ /// may return PUSH even after isShutdown() or may return SHUTDOWN
+ WaitResult decrOrPush(uint32_t& n, uint32_t idx) {
+ assert(n > 0);
+
+ while (true) {
+ auto head = head_.load(std::memory_order_acquire);
+
+ if (!head.isNodeIdx() && head.value() > 0) {
+ // decr
+ auto delta = std::min(n, head.value());
+ if (head_.compare_exchange_strong(head, head.withValueDecr(delta))) {
+ n -= delta;
+ return WaitResult::DECR;
+ }
+ } else {
+ // push
+ if (idx == 0) {
+ return WaitResult::PUSH;
+ }
+
+ if (UNLIKELY(head.isShutdown())) {
+ return WaitResult::SHUTDOWN;
+ }
+
+ auto& node = idxToNode(idx);
+ node.next = head.isNodeIdx() ? head.idx() : 0;
+ if (head_.compare_exchange_strong(head, head.withPush(idx))) {
+ // push succeeded
+ return WaitResult::PUSH;
+ }
+ }
+ }
+ // retry
+ }
+};
+
+} // namespace detail
+
+template <template<typename> class Atom, class BatonType>
+struct LifoSemImpl : public detail::LifoSemBase<BatonType, Atom> {
+ explicit LifoSemImpl(uint32_t v = 0)
+ : detail::LifoSemBase<BatonType, Atom>(v) {}
+};
+
+} // namespace folly
+
+#endif
--- /dev/null
+/*
+ * Copyright 2014 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "folly/LifoSem.h"
+#include "folly/test/DeterministicSchedule.h"
+
+#include <thread>
+#include <semaphore.h>
+#include <gflags/gflags.h>
+#include <gtest/gtest.h>
+
+#include "folly/Benchmark.h"
+#include "folly/Random.h"
+
+using namespace folly;
+using namespace folly::test;
+
+typedef LifoSemImpl<DeterministicAtomic> DLifoSem;
+typedef DeterministicSchedule DSched;
+
+LIFOSEM_DECLARE_POOL(DeterministicAtomic, 100000)
+
+TEST(LifoSem, basic) {
+ LifoSem sem;
+ EXPECT_FALSE(sem.tryWait());
+ sem.post();
+ EXPECT_TRUE(sem.tryWait());
+ sem.post();
+ sem.wait();
+}
+
+TEST(LifoSem, multi) {
+ LifoSem sem;
+
+ const int opsPerThread = 10000;
+ std::thread threads[10];
+ std::atomic<int> blocks(0);
+
+ for (auto& thr : threads) {
+ thr = std::thread([&]{
+ int b = 0;
+ for (int i = 0; i < opsPerThread; ++i) {
+ if (!sem.tryWait()) {
+ sem.wait();
+ ++b;
+ }
+ sem.post();
+ }
+ blocks += b;
+ });
+ }
+
+ // start the flood
+ sem.post();
+
+ for (auto& thr : threads) {
+ thr.join();
+ }
+
+ LOG(INFO) << opsPerThread * sizeof(threads)/sizeof(threads[0])
+ << " post/wait pairs, " << blocks << " blocked";
+}
+
+TEST(LifoSem, pingpong) {
+ DSched sched(DSched::uniform(0));
+
+ const int iters = 100;
+
+ for (int pass = 0; pass < 10; ++pass) {
+ DLifoSem a;
+ DLifoSem b;
+
+ auto thr = DSched::thread([&]{
+ for (int i = 0; i < iters; ++i) {
+ a.wait();
+ // main thread can't be running here
+ EXPECT_EQ(a.valueGuess(), 0);
+ EXPECT_EQ(b.valueGuess(), 0);
+ b.post();
+ }
+ });
+ for (int i = 0; i < iters; ++i) {
+ a.post();
+ b.wait();
+ // child thread can't be running here
+ EXPECT_EQ(a.valueGuess(), 0);
+ EXPECT_EQ(b.valueGuess(), 0);
+ }
+ DSched::join(thr);
+ }
+}
+
+TEST(LifoSem, mutex) {
+ DSched sched(DSched::uniform(0));
+
+ const int iters = 100;
+
+ for (int pass = 0; pass < 10; ++pass) {
+ DLifoSem a;
+
+ auto thr = DSched::thread([&]{
+ for (int i = 0; i < iters; ++i) {
+ a.wait();
+ a.post();
+ }
+ });
+ for (int i = 0; i < iters; ++i) {
+ a.post();
+ a.wait();
+ }
+ a.post();
+ DSched::join(thr);
+ a.wait();
+ }
+}
+
+TEST(LifoSem, no_blocking) {
+ long seed = folly::randomNumberSeed() % 10000;
+ LOG(INFO) << "seed=" << seed;
+ DSched sched(DSched::uniform(seed));
+
+ const int iters = 100;
+ const int numThreads = 2;
+ const int width = 10;
+
+ for (int pass = 0; pass < 10; ++pass) {
+ DLifoSem a;
+
+ std::vector<std::thread> threads;
+ while (threads.size() < numThreads) {
+ threads.emplace_back(DSched::thread([&]{
+ for (int i = 0; i < iters; ++i) {
+ a.post(width);
+ for (int w = 0; w < width; ++w) {
+ a.wait();
+ }
+ }
+ }));
+ }
+ for (auto& thr : threads) {
+ DSched::join(thr);
+ }
+ }
+}
+
+TEST(LifoSem, one_way) {
+ long seed = folly::randomNumberSeed() % 10000;
+ LOG(INFO) << "seed=" << seed;
+ DSched sched(DSched::uniformSubset(seed, 1, 6));
+
+ const int iters = 1000;
+
+ for (int pass = 0; pass < 10; ++pass) {
+ DLifoSem a;
+
+ auto thr = DSched::thread([&]{
+ for (int i = 0; i < iters; ++i) {
+ a.wait();
+ }
+ });
+ for (int i = 0; i < iters; ++i) {
+ a.post();
+ }
+ DSched::join(thr);
+ }
+}
+
+TEST(LifoSem, shutdown_race) {
+ long seed = folly::randomNumberSeed() % 10000;
+ LOG(INFO) << "seed=" << seed;
+
+ bool shutdownWon = false;
+ bool shutdownLost = false;
+ for (int pass = 0; pass < 1000; ++pass) {
+ DSched sched(DSched::uniformSubset(seed + pass, 1, 1 + (pass % 50)));
+
+ DLifoSem a;
+ int waitCount = 0;
+ auto thr = DSched::thread([&]{
+ try {
+ while (true) {
+ a.wait();
+ ++waitCount;
+ }
+ } catch (ShutdownSemError& x) {
+ // expected
+ EXPECT_TRUE(a.isShutdown());
+ }
+ });
+ EXPECT_TRUE(!a.isShutdown());
+ a.shutdown();
+ EXPECT_TRUE(a.isShutdown());
+ a.post();
+ DSched::join(thr);
+ EXPECT_EQ(1, waitCount + a.valueGuess());
+ if (waitCount == 0) {
+ shutdownWon = true;
+ } else {
+ shutdownLost = true;
+ }
+ }
+ EXPECT_TRUE(shutdownWon);
+ EXPECT_TRUE(shutdownLost);
+}
+
+TEST(LifoSem, shutdown_multi) {
+ DSched sched(DSched::uniform(0));
+
+ for (int pass = 0; pass < 10; ++pass) {
+ DLifoSem a;
+ std::vector<std::thread> threads;
+ while (threads.size() < 20) {
+ threads.push_back(DSched::thread([&]{
+ try {
+ a.wait();
+ EXPECT_TRUE(false);
+ } catch (ShutdownSemError& x) {
+ // expected
+ EXPECT_TRUE(a.isShutdown());
+ }
+ }));
+ }
+ a.shutdown();
+ for (auto& thr : threads) {
+ DSched::join(thr);
+ }
+ }
+}
+
+TEST(LifoSem, multi_try_wait_simple) {
+ LifoSem sem;
+ sem.post(5);
+ auto n = sem.tryWait(10); // this used to trigger an assert
+ ASSERT_EQ(5, n);
+}
+
+TEST(LifoSem, multi_try_wait) {
+ long seed = folly::randomNumberSeed() % 10000;
+ LOG(INFO) << "seed=" << seed;
+ DSched sched(DSched::uniform(seed));
+ DLifoSem sem;
+
+ const int NPOSTS = 1000;
+
+ auto producer = [&]{
+ for (int i=0; i<NPOSTS; ++i) {
+ sem.post();
+ }
+ };
+
+ std::atomic<bool> consumer_stop;
+ int consumed = 0;
+
+ auto consumer = [&]{
+ bool stop;
+ do {
+ stop = consumer_stop.load();
+ int n;
+ do {
+ n = sem.tryWait(10);
+ consumed += n;
+ } while (n > 0);
+ } while (!stop);
+ };
+
+ std::thread producer_thread(DSched::thread(producer));
+ std::thread consumer_thread(DSched::thread(consumer));
+ DSched::join(producer_thread);
+ consumer_stop.store(true);
+ DSched::join(consumer_thread);
+
+ ASSERT_EQ(NPOSTS, consumed);
+}
+
+BENCHMARK(lifo_sem_pingpong, iters) {
+ LifoSem a;
+ LifoSem b;
+ auto thr = std::thread([&]{
+ for (int i = 0; i < iters; ++i) {
+ a.wait();
+ b.post();
+ }
+ });
+ for (int i = 0; i < iters; ++i) {
+ a.post();
+ b.wait();
+ }
+ thr.join();
+}
+
+BENCHMARK(lifo_sem_oneway, iters) {
+ LifoSem a;
+ auto thr = std::thread([&]{
+ for (int i = 0; i < iters; ++i) {
+ a.wait();
+ }
+ });
+ for (int i = 0; i < iters; ++i) {
+ a.post();
+ }
+ thr.join();
+}
+
+BENCHMARK(single_thread_lifo_post, iters) {
+ LifoSem sem;
+ for (int n = 0; n < iters; ++n) {
+ sem.post();
+ asm volatile ("":::"memory");
+ }
+}
+
+BENCHMARK(single_thread_lifo_wait, iters) {
+ LifoSem sem(iters);
+ for (int n = 0; n < iters; ++n) {
+ sem.wait();
+ asm volatile ("":::"memory");
+ }
+}
+
+BENCHMARK(single_thread_lifo_postwait, iters) {
+ LifoSem sem;
+ for (int n = 0; n < iters; ++n) {
+ sem.post();
+ asm volatile ("":::"memory");
+ sem.wait();
+ asm volatile ("":::"memory");
+ }
+}
+
+BENCHMARK(single_thread_lifo_trywait, iters) {
+ LifoSem sem;
+ for (int n = 0; n < iters; ++n) {
+ EXPECT_FALSE(sem.tryWait());
+ asm volatile ("":::"memory");
+ }
+}
+
+BENCHMARK(single_thread_posix_postwait, iters) {
+ sem_t sem;
+ EXPECT_EQ(sem_init(&sem, 0, 0), 0);
+ for (int n = 0; n < iters; ++n) {
+ EXPECT_EQ(sem_post(&sem), 0);
+ EXPECT_EQ(sem_wait(&sem), 0);
+ }
+ EXPECT_EQ(sem_destroy(&sem), 0);
+}
+
+BENCHMARK(single_thread_posix_trywait, iters) {
+ sem_t sem;
+ EXPECT_EQ(sem_init(&sem, 0, 0), 0);
+ for (int n = 0; n < iters; ++n) {
+ EXPECT_EQ(sem_trywait(&sem), -1);
+ }
+ EXPECT_EQ(sem_destroy(&sem), 0);
+}
+
+static void contendedUse(uint n, int posters, int waiters) {
+ LifoSemImpl<std::atomic> sem;
+
+ std::vector<std::thread> threads;
+ std::atomic<bool> go(false);
+
+ BENCHMARK_SUSPEND {
+ for (int t = 0; t < waiters; ++t) {
+ threads.emplace_back([=,&sem] {
+ for (uint i = t; i < n; i += waiters) {
+ sem.wait();
+ }
+ });
+ }
+ for (int t = 0; t < posters; ++t) {
+ threads.emplace_back([=,&sem,&go] {
+ while (!go.load()) {
+ std::this_thread::yield();
+ }
+ for (uint i = t; i < n; i += posters) {
+ sem.post();
+ }
+ });
+ }
+ }
+
+ go.store(true);
+ for (auto& thr : threads) {
+ thr.join();
+ }
+}
+
+BENCHMARK_DRAW_LINE()
+BENCHMARK_NAMED_PARAM(contendedUse, 1_to_1, 1, 1)
+BENCHMARK_NAMED_PARAM(contendedUse, 1_to_32, 1, 32)
+BENCHMARK_NAMED_PARAM(contendedUse, 32_to_1, 31, 1)
+BENCHMARK_NAMED_PARAM(contendedUse, 16_to_16, 16, 16)
+BENCHMARK_NAMED_PARAM(contendedUse, 32_to_32, 32, 32)
+BENCHMARK_NAMED_PARAM(contendedUse, 32_to_1000, 32, 1000)
+
+// sudo nice -n -20 tao/queues/LifoSemTests --benchmark --bm_min_iters=10000000
+// ============================================================================
+// tao/queues/LifoSemTests.cpp relative time/iter iters/s
+// ============================================================================
+// lifo_sem_pingpong 1.91us 522.92K
+// lifo_sem_oneway 211.18ns 4.74M
+// single_thread_lifo_post 19.71ns 50.75M
+// single_thread_lifo_wait 18.84ns 53.09M
+// single_thread_lifo_postwait 39.41ns 25.37M
+// single_thread_lifo_trywait 912.10ps 1.10G
+// single_thread_posix_postwait 32.93ns 30.37M
+// single_thread_posix_trywait 10.06ns 99.36M
+// ----------------------------------------------------------------------------
+// contendedUse(1_to_1) 208.21ns 4.80M
+// contendedUse(1_to_32) 532.41ns 1.88M
+// contendedUse(32_to_1) 153.74ns 6.50M
+// contendedUse(16_to_16) 301.86ns 3.31M
+// contendedUse(32_to_32) 268.32ns 3.73M
+// contendedUse(32_to_1000) 966.27ns 1.03M
+// ============================================================================
+
+int main(int argc, char ** argv) {
+ testing::InitGoogleTest(&argc, argv);
+ google::ParseCommandLineFlags(&argc, &argv, true);
+ int rv = RUN_ALL_TESTS();
+ folly::runBenchmarksOnFlag();
+ return rv;
+}
projects / folly.git / commitdiff