Add IoUringBackend::NotAvailable exception

Summary: Add IoUringBackend::NotAvailable exception

Reviewed By: kevin-vigor

Differential Revision: D19143143

fbshipit-source-id: 7b55106d50882d34fc6100a81ff2a4e5748e9b85

folly/experimental/io/IoUringBackend.cpp

@@ -37,7 +37,7 @@ IoUringBackend::IoUringBackend(size_t capacity, size_t maxSubmit, size_t maxGet)
                << params_.cq_entries << ") "
                << "failed errno = " << errno << ":\"" << folly::errnoStr(errno)
                << "\" " << this;
-    throw std::runtime_error("io_uring_queue_init error");
+    throw NotAvailable("io_uring_queue_init error");
   }
 
   sqRingMask_ = *ioRing_.sq.kring_mask;
@@ -63,7 +63,7 @@ IoUringBackend::IoUringBackend(size_t capacity, size_t maxSubmit, size_t maxGet)
   if (!addTimerFd()) {
     cleanup();
     entries_.reset();
-    throw std::runtime_error("io_uring_submit error");
+    throw NotAvailable("io_uring_submit error");
   }
 }
 
@@ -87,7 +87,7 @@ bool IoUringBackend::isAvailable() {
   folly::call_once(initFlag, [&]() {
     try {
       IoUringBackend backend(1024, 128);
-    } catch (const std::runtime_error&) {
+    } catch (const NotAvailable&) {
       sAvailable = false;
     }
   });

folly/experimental/io/IoUringBackend.h

@@ -27,6 +27,12 @@ namespace folly {
 
 class IoUringBackend : public PollIoBackend {
  public:
+  class NotAvailable : public std::runtime_error {
+   public:
+    explicit NotAvailable(const std::string& what) noexcept
+        : std::runtime_error(what) {}
+  };
+
   explicit IoUringBackend(
       size_t capacity,
       size_t maxSubmit = 128,