MDEV-16264: Add threadpool library

The library is capable of
- asynchronous execution of tasks (and optionally waiting for them)
- asynchronous file IO
  This is implemented using libaio on Linux and completion ports on
  Windows. Elsewhere, async io is "simulated", which means worker threads
  are performing synchronous IO.
- timers, scheduling work asynchronously in some point of the future.
  Also periodic timers are implemented.

tpool/aio_linux.cc

@@ -0,0 +1,157 @@
+/* Copyright(C) 2019 MariaDB Corporation.
+
+This program is free software; you can redistribute itand /or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; version 2 of the License.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02111 - 1301 USA*/
+
+#include "tpool_structs.h"
+
+#include <stdlib.h>
+#include <signal.h>
+#include <assert.h>
+#include "tpool.h"
+#include <thread>
+#ifdef LINUX_NATIVE_AIO
+#include <libaio.h>
+#endif
+/*
+  Linux AIO implementation, based on native AIO.
+  Needs libaio.h and -laio at the compile time.
+
+  submit_io() is used to submit async IO.
+
+  There is a single thread, that collects the completion notification
+  with  io_getevent(), and forwards io completion callback
+  the worker threadpool.
+*/
+namespace tpool
+{
+#ifdef LINUX_NATIVE_AIO
+
+class aio_linux : public aio
+{
+  int m_max_io_count;
+  thread_pool* m_pool;
+  io_context_t m_io_ctx;
+  bool m_in_shutdown;
+  std::thread m_getevent_thread;
+
+  static void getevent_thread_routine(aio_linux* aio)
+  {
+    for (;;)
+    {
+      io_event event;
+      struct timespec ts{0, 500000000};
+      int ret = io_getevents(aio->m_io_ctx, 1, 1, &event, &ts);
+
+      if (aio->m_in_shutdown)
+        break;
+
+      if (ret > 0)
+      {
+        aiocb* iocb = (aiocb*)event.obj;
+        long long res = event.res;
+        if (res < 0)
+        {
+          iocb->m_err = -res;
+          iocb->m_ret_len = 0;
+        }
+        else
+        {
+          iocb->m_ret_len = ret;
+          iocb->m_err = 0;
+        }
+
+        iocb->m_internal_task.m_func = iocb->m_callback;
+        iocb->m_internal_task.m_arg = iocb;
+        iocb->m_internal_task.m_group = iocb->m_group;
+        aio->m_pool->submit_task(&iocb->m_internal_task);
+        continue;
+      }
+      switch (ret)
+      {
+      case -EAGAIN:
+        usleep(1000);
+        continue;
+      case -EINTR:
+      case 0:
+        continue;
+      default:
+        fprintf(stderr, "io_getevents returned %d\n", ret);
+        abort();
+      }
+    }
+  }
+
+public:
+  aio_linux(io_context_t ctx, thread_pool* pool, size_t max_count)
+    : m_max_io_count(max_count), m_pool(pool), m_io_ctx(ctx),
+    m_in_shutdown(), m_getevent_thread(getevent_thread_routine, this)
+  {
+  }
+
+  ~aio_linux()
+  {
+    m_in_shutdown = true;
+    m_getevent_thread.join();
+    io_destroy(m_io_ctx);
+  }
+
+  // Inherited via aio
+  virtual int submit_io(aiocb* cb) override
+  {
+
+    if (cb->m_opcode == aio_opcode::AIO_PREAD)
+      io_prep_pread((iocb *)cb, cb->m_fh, cb->m_buffer, cb->m_len,
+        cb->m_offset);
+    else
+      io_prep_pwrite((iocb *)cb, cb->m_fh, cb->m_buffer, cb->m_len,
+        cb->m_offset);
+
+    int ret;
+    ret = io_submit(m_io_ctx, 1, (iocb * *)& cb);
+    if (ret == 1)
+      return 0;
+    errno = -ret;
+    return -1;
+  }
+
+  // Inherited via aio
+  virtual int bind(native_file_handle& fd) override
+  {
+    return 0;
+  }
+  virtual int unbind(const native_file_handle& fd) override
+  {
+    return 0;
+  }
+};
+
+aio* create_linux_aio(thread_pool* pool, int max_io)
+{
+  io_context_t ctx;
+  memset(&ctx, 0, sizeof(ctx));
+  int ret = io_setup(max_io, &ctx);
+  if (ret)
+  {
+    fprintf(stderr, "io_setup(%d) returned %d\n", max_io, ret);
+    return nullptr;
+  }
+  return new aio_linux(ctx, pool, max_io);
+}
+#else
+aio* create_linux_aio(thread_pool* pool, int max_aio)
+{
+  return nullptr;
+}
+#endif
+}