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.

3 files changed, 98 insertions, 0 deletions

diff --git a/library/cpp/threading/cron/cron.cpp b/library/cpp/threading/cron/cron.cpp
new file mode 100644
index 0000000000..e7c1c59735
--- /dev/null
+++ b/library/cpp/threading/cron/cron.cpp
@@ -0,0 +1,69 @@
+#include "cron.h"
+
+#include <library/cpp/deprecated/atomic/atomic.h>
+
+#include <util/system/thread.h>
+#include <util/system/event.h>
+
+using namespace NCron;
+
+namespace {
+    struct TPeriodicHandle: public IHandle {
+        inline TPeriodicHandle(TJob job, TDuration interval, const TString& threadName)
+            : Job(job)
+            , Interval(interval)
+            , Done(false)
+        {
+            TThread::TParams params(DoRun, this);
+            if (!threadName.empty()) {
+                params.SetName(threadName);
+            }
+            Thread = MakeHolder<TThread>(params);
+            Thread->Start();
+        }
+
+        static inline void* DoRun(void* data) noexcept {
+            ((TPeriodicHandle*)data)->Run();
+
+            return nullptr;
+        }
+
+        inline void Run() noexcept {
+            while (true) {
+                Job();
+
+                Event.WaitT(Interval);
+
+                if (AtomicGet(Done)) {
+                    return;
+                }
+            }
+        }
+
+        ~TPeriodicHandle() override {
+            AtomicSet(Done, true);
+            Event.Signal();
+            Thread->Join();
+        }
+
+        TJob Job;
+        TDuration Interval;
+        TManualEvent Event;
+        TAtomic Done;
+        THolder<TThread> Thread;
+    };
+}
+
+IHandlePtr NCron::StartPeriodicJob(TJob job) {
+    return NCron::StartPeriodicJob(job, TDuration::Seconds(0), "");
+}
+
+IHandlePtr NCron::StartPeriodicJob(TJob job, TDuration interval) {
+    return NCron::StartPeriodicJob(job, interval, "");
+}
+
+IHandlePtr NCron::StartPeriodicJob(TJob job, TDuration interval, const TString& threadName) {
+    return new TPeriodicHandle(job, interval, threadName);
+}
+
+IHandle::~IHandle() = default;
diff --git a/library/cpp/threading/cron/cron.h b/library/cpp/threading/cron/cron.h
new file mode 100644
index 0000000000..77fa40c5e2
--- /dev/null
+++ b/library/cpp/threading/cron/cron.h
@@ -0,0 +1,18 @@
+#pragma once
+
+#include <util/generic/ptr.h>
+#include <util/generic/function.h>
+#include <util/datetime/base.h>
+
+namespace NCron {
+    struct IHandle {
+        virtual ~IHandle();
+    };
+
+    using TJob = std::function<void()>;
+    using IHandlePtr = TAutoPtr<IHandle>;
+
+    IHandlePtr StartPeriodicJob(TJob job);
+    IHandlePtr StartPeriodicJob(TJob job, TDuration interval);
+    IHandlePtr StartPeriodicJob(TJob job, TDuration interval, const TString& threadName);
+}
diff --git a/library/cpp/threading/cron/ya.make b/library/cpp/threading/cron/ya.make
new file mode 100644
index 0000000000..ead272e837
--- /dev/null
+++ b/library/cpp/threading/cron/ya.make
@@ -0,0 +1,11 @@
+LIBRARY()
+
+SRCS(
+    cron.cpp
+)
+
+PEERDIR(
+    library/cpp/deprecated/atomic
+)
+
+END()