YT-19324: move YT provider to ydb/library/yql

This commit is formed by the following script: https://paste.yandex-team.ru/6f92e4b8-efc5-4d34-948b-15ee2accd7e7/text.
This commit has zero effect on all projects that depend on YQL.

The summary of changes:
- `yql/providers/yt -> ydb/library/yql/providers/yt `- the whole implementation of YT provider is moved into YDB code base for further export as a part of YT YQL plugin shared library;
- `yql/providers/stat/{expr_nodes,uploader} -> ydb/library/yql/providers/stat/{expr_nodes,uploader}` - a small interface without implementation and the description of stat expr nodes;
- `yql/core/extract_predicate/ut -> ydb/library/yql/core/extract_predicate/ut`;
- `yql/core/{ut,ut_common} -> ydb/library/yql/core/{ut,ut_common}`;
- `yql/core` is gone;
- `yql/library/url_preprocessing -> ydb/library/yql/core/url_preprocessing`.

**NB**: all new targets inside `ydb/` are under `IF (NOT CMAKE_EXPORT)` clause which disables them from open-source cmake generation and ya make build. They will be enabled in the subsequent commits.

1 files changed, 158 insertions, 0 deletions

diff --git a/library/cpp/threading/blocking_queue/blocking_queue.h b/library/cpp/threading/blocking_queue/blocking_queue.h
new file mode 100644
index 0000000000..48d3762f68
--- /dev/null
+++ b/library/cpp/threading/blocking_queue/blocking_queue.h
@@ -0,0 +1,158 @@
+#pragma once
+
+#include <util/generic/deque.h>
+#include <util/generic/maybe.h>
+#include <util/generic/yexception.h>
+#include <util/system/condvar.h>
+#include <util/system/guard.h>
+#include <util/system/mutex.h>
+
+#include <utility>
+
+namespace NThreading {
+    ///
+    /// TBlockingQueue is a queue of elements of limited or unlimited size.
+    /// Queue provides Push and Pop operations that block if operation can't be executed
+    /// (queue is empty or maximum size is reached).
+    ///
+    /// Queue can be stopped, in that case all blocked operation will return `Nothing` / false.
+    ///
+    /// All operations are thread safe.
+    ///
+    ///
+    /// Example of usage:
+    ///     TBlockingQueue<int> queue;
+    ///
+    ///     ...
+    ///
+    ///     // thread 1
+    ///     queue.Push(42);
+    ///     queue.Push(100500);
+    ///
+    ///     ...
+    ///
+    ///     // thread 2
+    ///     while (TMaybe<int> number = queue.Pop()) {
+    ///         ProcessNumber(number.GetRef());
+    ///     }
+    template <class TElement>
+    class TBlockingQueue {
+    public:
+        ///
+        /// Creates blocking queue with given maxSize
+        /// if maxSize == 0 then queue is unlimited
+        TBlockingQueue(size_t maxSize)
+            : MaxSize(maxSize == 0 ? Max<size_t>() : maxSize)
+            , Stopped(false)
+        {
+        }
+
+        ///
+        /// Blocks until queue has some elements or queue is stopped or deadline is reached.
+        /// Returns `Nothing` if queue is stopped or deadline is reached.
+        /// Returns element otherwise.
+        TMaybe<TElement> Pop(TInstant deadline = TInstant::Max()) {
+            TGuard<TMutex> g(Lock);
+
+            const auto canPop = [this]() { return CanPop(); };
+            if (!CanPopCV.WaitD(Lock, deadline, canPop)) {
+                return Nothing();
+            }
+
+            if (Stopped && Queue.empty()) {
+                return Nothing();
+            }
+            TElement e = std::move(Queue.front());
+            Queue.pop_front();
+            CanPushCV.Signal();
+            return std::move(e);
+        }
+
+        TMaybe<TElement> Pop(TDuration duration) {
+            return Pop(TInstant::Now() + duration);
+        }
+
+        ///
+        /// Blocks until queue has space for new elements or queue is stopped or deadline is reached.
+        /// Returns false exception if queue is stopped and push failed or deadline is reached.
+        /// Pushes element to queue and returns true otherwise.
+        bool Push(const TElement& e, TInstant deadline = TInstant::Max()) {
+            return PushRef(e, deadline);
+        }
+
+        bool Push(TElement&& e, TInstant deadline = TInstant::Max()) {
+            return PushRef(std::move(e), deadline);
+        }
+
+        bool Push(const TElement& e, TDuration duration) {
+            return Push(e, TInstant::Now() + duration);
+        }
+
+        bool Push(TElement&& e, TDuration duration) {
+            return Push(std::move(e), TInstant::Now() + duration);
+        }
+
+        ///
+        /// Stops the queue, all blocked operations will be aborted.
+        void Stop() {
+            TGuard<TMutex> g(Lock);
+            Stopped = true;
+            CanPopCV.BroadCast();
+            CanPushCV.BroadCast();
+        }
+
+        ///
+        /// Checks whether queue is empty.
+        bool Empty() const {
+            TGuard<TMutex> g(Lock);
+            return Queue.empty();
+        }
+
+        ///
+        /// Returns size of the queue.
+        size_t Size() const {
+            TGuard<TMutex> g(Lock);
+            return Queue.size();
+        }
+
+        ///
+        /// Checks whether queue is stopped.
+        bool IsStopped() const {
+            TGuard<TMutex> g(Lock);
+            return Stopped;
+        }
+
+    private:
+        bool CanPush() const {
+            return Queue.size() < MaxSize || Stopped;
+        }
+
+        bool CanPop() const {
+            return !Queue.empty() || Stopped;
+        }
+
+        template <typename Ref>
+        bool PushRef(Ref e, TInstant deadline) {
+            TGuard<TMutex> g(Lock);
+            const auto canPush = [this]() { return CanPush(); };
+            if (!CanPushCV.WaitD(Lock, deadline, canPush)) {
+                return false;
+            }
+            if (Stopped) {
+                return false;
+            }
+            Queue.push_back(std::forward<TElement>(e));
+            CanPopCV.Signal();
+            return true;
+        }
+
+    private:
+        TMutex Lock;
+        TCondVar CanPopCV;
+        TCondVar CanPushCV;
+        TDeque<TElement> Queue;
+        size_t MaxSize;
+        bool Stopped;
+    };
+
+}