Add pending operations presence check function, fixes #5155

lib/pure/asyncdispatch.nim

@@ -254,8 +254,14 @@ when defined(windows) or defined(nimdoc):
         "Operation performed on a socket which has not been registered with" &
         " the dispatcher yet.")
 
+  proc hasPendingOperations*(): bool =
+    ## Returns `true` if the global dispatcher has pending operations.
+    let p = getGlobalDispatcher()
+    p.handles.len != 0 or p.timers.len != 0 or p.callbacks.len != 0
+
   proc poll*(timeout = 500) =
-    ## Waits for completion events and processes them.
+    ## Waits for completion events and processes them. Raises ``ValueError``
+    ## if there are no pending operations.
     let p = getGlobalDispatcher()
     if p.handles.len == 0 and p.timers.len == 0 and p.callbacks.len == 0:
       raise newException(ValueError,
@@ -1056,8 +1062,15 @@ else:
           newCBs.add(cb)
     callbacks = newCBs & callbacks
 
+  proc hasPendingOperations*(): bool =
+    let p = getGlobalDispatcher()
+    p.selector.len != 0 or p.timers.len != 0 or p.callbacks.len != 0
+
   proc poll*(timeout = 500) =
     let p = getGlobalDispatcher()
+    if p.selector.len == 0 and p.timers.len == 0 and p.callbacks.len == 0:
+      raise newException(ValueError,
+        "No handles or timers registered in dispatcher.")
 
     if p.selector.len > 0:
       for info in p.selector.select(p.adjustedTimeout(timeout)):

lib/upcoming/asyncdispatch.nim

@@ -231,8 +231,14 @@ when defined(windows) or defined(nimdoc):
         "Operation performed on a socket which has not been registered with" &
         " the dispatcher yet.")
 
+  proc hasPendingOperations*(): bool =
+    ## Returns `true` if the global dispatcher has pending operations.
+    let p = getGlobalDispatcher()
+    p.handles.len != 0 or p.timers.len != 0 or p.callbacks.len != 0
+
   proc poll*(timeout = 500) =
-    ## Waits for completion events and processes them.
+    ## Waits for completion events and processes them. Raises ``ValueError``
+    ## if there are no pending operations.
     let p = getGlobalDispatcher()
     if p.handles.len == 0 and p.timers.len == 0 and p.callbacks.len == 0:
       raise newException(ValueError,
@@ -1182,6 +1188,10 @@ else:
       raise newException(ValueError, "File descriptor not registered.")
     p.selector.updateHandle(fd.SocketHandle, newEvents)
 
+  proc hasPendingOperations*(): bool =
+    let p = getGlobalDispatcher()
+    not p.selector.isEmpty() or p.timers.len != 0 or p.callbacks.len != 0
+
   proc poll*(timeout = 500) =
     var keys: array[64, ReadyKey[AsyncData]]
 

tests/async/tpendingcheck.nim

@@ -0,0 +1,21 @@
+discard """
+  file: "tpendingcheck.nim"
+  exitcode: 0
+  output: ""
+"""
+
+import asyncdispatch
+
+doAssert(not hasPendingOperations())
+
+proc test() {.async.} =
+  await sleepAsync(100)
+
+var f = test()
+while not f.finished:
+  doAssert(hasPendingOperations())
+  poll(10)
+f.read
+
+doAssert(not hasPendingOperations())
+