Fix long shutdown of FileLog storage

Previously it was possible to wait up to
poll_directory_watch_events_backoff_max (default is 32000) on shutdown,
because it was not possible to stop poll of inotify.

Before (takes 3 seconds):

    2024.02.12 11:27:55.058192 [ 10134 ] {} <Trace> StorageFileLog (file_log): Waiting for cleanup
    2024.02.12 11:27:58.178021 [ 10271 ] {} <Trace> directory_watch: Execution took 7519 ms.

After:

    2024.02.12 11:33:29.722403 [ 15866 ] {} <Trace> StorageFileLog (file_log): Waiting for cleanup
    2024.02.12 11:33:29.722473 [ 15956 ] {} <Trace> directory_watch: Execution took 6399 ms.

Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>

src/Storages/FileLog/DirectoryWatcherBase.cpp

@@ -34,8 +34,8 @@ DirectoryWatcherBase::DirectoryWatcherBase(
     if (!std::filesystem::is_directory(path))
         throw Exception(ErrorCodes::BAD_FILE_TYPE, "Path {} is not a directory", path);
 
-    fd = inotify_init();
-    if (fd == -1)
+    inotify_fd = inotify_init();
+    if (inotify_fd == -1)
         throw ErrnoException(ErrorCodes::IO_SETUP_ERROR, "Cannot initialize inotify");
 
     watch_task = getContext()->getSchedulePool().createTask("directory_watch", [this] { watchFunc(); });
@@ -56,7 +56,7 @@ void DirectoryWatcherBase::watchFunc()
     if (eventMask() & DirectoryWatcherBase::DW_ITEM_MOVED_TO)
         mask |= IN_MOVED_TO;
 
-    int wd = inotify_add_watch(fd, path.c_str(), mask);
+    int wd = inotify_add_watch(inotify_fd, path.c_str(), mask);
     if (wd == -1)
     {
         owner.onError(Exception(ErrorCodes::IO_SETUP_ERROR, "Watch directory {} failed", path));
@@ -65,16 +65,20 @@ void DirectoryWatcherBase::watchFunc()
 
     std::string buffer;
     buffer.resize(buffer_size);
-    pollfd pfd;
-    pfd.fd = fd;
-    pfd.events = POLLIN;
+    pollfd pfds[2];
+    /// inotify descriptor
+    pfds[0].fd = inotify_fd;
+    pfds[0].events = POLLIN;
+    // notifier
+    pfds[1].fd = event_pipe.fds_rw[0];
+    pfds[1].events = POLLIN;
     while (!stopped)
     {
         const auto & settings = owner.storage.getFileLogSettings();
-        if (poll(&pfd, 1, static_cast<int>(milliseconds_to_wait)) > 0 && pfd.revents & POLLIN)
+        if (poll(pfds, 2, static_cast<int>(milliseconds_to_wait)) > 0 && pfds[0].revents & POLLIN)
         {
             milliseconds_to_wait = settings->poll_directory_watch_events_backoff_init.totalMilliseconds();
-            ssize_t n = read(fd, buffer.data(), buffer.size());
+            ssize_t n = read(inotify_fd, buffer.data(), buffer.size());
             int i = 0;
             if (n > 0)
             {
@@ -130,7 +134,7 @@ void DirectoryWatcherBase::watchFunc()
 DirectoryWatcherBase::~DirectoryWatcherBase()
 {
     stop();
-    int err = ::close(fd);
+    int err = ::close(inotify_fd);
     chassert(!err || errno == EINTR);
 }
 
@@ -143,6 +147,7 @@ void DirectoryWatcherBase::start()
 void DirectoryWatcherBase::stop()
 {
     stopped = true;
+    ::write(event_pipe.fds_rw[1], "\0", 1);
     if (watch_task)
         watch_task->deactivate();
 }

src/Storages/FileLog/DirectoryWatcherBase.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <Core/BackgroundSchedulePool.h>
+#include <Common/PipeFDs.h>
 
 #include <atomic>
 #include <memory>
@@ -85,10 +86,6 @@ public:
 
     void watchFunc();
 
-protected:
-    void start();
-    void stop();
-
 private:
     FileLogDirectoryWatcher & owner;
 
@@ -102,7 +99,11 @@ private:
     int event_mask;
     uint64_t milliseconds_to_wait;
 
-    int fd;
+    int inotify_fd;
+    PipeFDs event_pipe;
+
+    void start();
+    void stop();
 };
 
 }