retry when epoll_wait fails with EINTR (#1801)

* retry when epoll_wait fails with EINTR

* add error code to exception message

* retry on EINTR for first time call too

src/System.Device.Gpio/Interop/Unix/Libc/Interop.epoll_wait.cs

@@ -8,6 +8,6 @@ using System.Runtime.InteropServices;
 
 internal partial class Interop
 {
-    [DllImport(LibcLibrary)]
+    [DllImport(LibcLibrary, SetLastError = true)]
     internal static extern int epoll_wait(int epfd, out epoll_event events, int maxevents, int timeout);
 }

src/System.Device.Gpio/System/Device/Gpio/Drivers/SysFsDriver.cs

@@ -6,6 +6,7 @@ using System.Diagnostics;
 using System.Globalization;
 using System.IO;
 using System.Linq;
+using System.Runtime.InteropServices;
 using System.Threading;
 
 namespace System.Device.Gpio.Drivers
@@ -15,6 +16,8 @@ namespace System.Device.Gpio.Drivers
     /// </summary>
     public class SysFsDriver : UnixDriver
     {
+        private const int ERROR_CODE_EINTR = 4; // Interrupted system call
+
         private const string GpioBasePath = "/sys/class/gpio";
         private const string GpioChip = "gpiochip";
         private const string GpioLabel = "/label";
@@ -442,7 +445,15 @@ namespace System.Device.Gpio.Drivers
             }
 
             // Ignore first time because it will always return the current state.
-            Interop.epoll_wait(pollFileDescriptor, out _, 1, 0);
+            while (Interop.epoll_wait(pollFileDescriptor, out _, 1, 0) == -1)
+            {
+                var errorCode = Marshal.GetLastWin32Error();
+                if (errorCode != ERROR_CODE_EINTR)
+                {
+                    // don't retry on unknown error
+                    break;
+                }
+            }
         }
 
         private unsafe bool WasEventDetected(int pollFileDescriptor, int valueFileDescriptor, out int pinNumber, CancellationToken cancellationToken)
@@ -457,7 +468,14 @@ namespace System.Device.Gpio.Drivers
                 int waitResult = Interop.epoll_wait(pollFileDescriptor, out epoll_event events, 1, PollingTimeout);
                 if (waitResult == -1)
                 {
-                    throw new IOException("Error while waiting for pin interrupts.");
+                    var errorCode = Marshal.GetLastWin32Error();
+                    if (errorCode == ERROR_CODE_EINTR)
+                    {
+                        // ignore Interrupted system call error and retry
+                        continue;
+                    }
+
+                    throw new IOException($"Error while waiting for pin interrupts. (ErrorCode={errorCode})");
                 }
 
                 if (waitResult > 0)