waitSignal() helper and tests for it. (#289)

* Add waitForSignal() implementation and tests.

* Fix compilation issues.

* Fix mistype.

* Rename to waitSignal().

* Fix Windows compilation issue.

* Re-export posix signals.

* Remove signal handler on continuation too.

chronos/asyncloop.nim

@@ -174,7 +174,13 @@ when defined(windows):
 elif unixPlatform:
   import ./selectors2
   from posix import EINTR, EAGAIN, EINPROGRESS, EWOULDBLOCK, MSG_PEEK,
-                    MSG_NOSIGNAL, SIGPIPE
+                    MSG_NOSIGNAL
+  from posix import SIGHUP, SIGINT, SIGQUIT, SIGILL, SIGTRAP, SIGABRT,
+                    SIGBUS, SIGFPE, SIGKILL, SIGUSR1, SIGSEGV, SIGUSR2,
+                    SIGPIPE, SIGALRM, SIGTERM, SIGPIPE
+  export SIGHUP, SIGINT, SIGQUIT, SIGILL, SIGTRAP, SIGABRT,
+         SIGBUS, SIGFPE, SIGKILL, SIGUSR1, SIGSEGV, SIGUSR2,
+         SIGPIPE, SIGALRM, SIGTERM, SIGPIPE
 
 type
   CallbackFunc* = proc (arg: pointer) {.gcsafe, raises: [Defect].}
@@ -851,6 +857,50 @@ proc callIdle*(cbproc: CallbackFunc) {.gcsafe, raises: [Defect].} =
 
 include asyncfutures2
 
+when not(defined(windows)):
+  when ioselSupportedPlatform:
+    proc waitSignal*(signal: int): Future[void] {.
+         raises: [Defect].} =
+      var retFuture = newFuture[void]("chronos.waitSignal()")
+      var sigfd: int = -1
+
+      template getSignalException(e: untyped): untyped =
+        newException(AsyncError, "Could not manipulate signal handler, " &
+                     "reason [" & $e.name & "]: " & $e.msg)
+
+      proc continuation(udata: pointer) {.gcsafe.} =
+        if not(retFuture.finished()):
+          if sigfd != -1:
+            try:
+              removeSignal(sigfd)
+              retFuture.complete()
+            except IOSelectorsException as exc:
+              retFuture.fail(getSignalException(exc))
+
+      proc cancellation(udata: pointer) {.gcsafe.} =
+        if not(retFuture.finished()):
+          if sigfd != -1:
+            try:
+              removeSignal(sigfd)
+            except IOSelectorsException as exc:
+              retFuture.fail(getSignalException(exc))
+
+      sigfd =
+        try:
+          addSignal(signal, continuation)
+        except IOSelectorsException as exc:
+          retFuture.fail(getSignalException(exc))
+          return retFuture
+        except ValueError as exc:
+          retFuture.fail(getSignalException(exc))
+          return retFuture
+        except OSError as exc:
+          retFuture.fail(getSignalException(exc))
+          return retFuture
+
+      retFuture.cancelCallback = cancellation
+      retFuture
+
 proc sleepAsync*(duration: Duration): Future[void] =
   ## Suspends the execution of the current async procedure for the next
   ## ``duration`` time.

tests/testsignal.nim

@@ -38,13 +38,33 @@ suite "Signal handling test suite":
       discard posix.kill(posix.getpid(), cint(signal))
       waitFor(fut)
       signalCounter == value
-  else:
-    const
-      SIGINT = 0
-      SIGTERM = 0
-    proc test(signal, value: int): bool = true
+
+    proc testWait(signal: int): bool =
+      var fut = waitSignal(signal)
+      discard posix.kill(posix.getpid(), cint(signal))
+      waitFor(fut)
+      true
 
   test "SIGINT test":
-    check test(SIGINT, 31337) == true
+    when not defined(windows):
+      check test(SIGINT, 31337) == true
+    else:
+      skip()
+
   test "SIGTERM test":
-    check test(SIGTERM, 65537) == true
+    when defined(windows):
+      skip()
+    else:
+      check test(SIGTERM, 65537) == true
+
+  test "waitSignal(SIGINT) test":
+    when defined(windows):
+      skip()
+    else:
+      check testWait(SIGINT) == true
+
+  test "waitSignal(SIGTERM) test":
+    when defined(windows):
+      skip()
+    else:
+      check testWait(SIGTERM) == true