Index: src/OFStreamObserver.h
==================================================================
--- src/OFStreamObserver.h
+++ src/OFStreamObserver.h
@@ -176,10 +176,19 @@
  * \param timeout The time to wait for an event, in seconds
  * \return A boolean whether events occurred during the timeinterval
  */
 - (BOOL)observeWithTimeout: (double)timeout;
 
+/**
+ * \brief Cancels the currently blocking observe call.
+ *
+ * This is automatically done when a new stream is added or removed by another
+ * thread, but in some circumstances, it might be desirable for a thread to
+ * manually stop the observe running in another thread.
+ */
+- (void)cancel;
+
 - (void)_addFileDescriptorForReading: (int)fd;
 - (void)_addFileDescriptorForWriting: (int)fd;
 - (void)_removeFileDescriptorForReading: (int)fd;
 - (void)_removeFileDescriptorForWriting: (int)fd;
 - (void)_processQueue;

Index: src/OFStreamObserver.m
==================================================================
--- src/OFStreamObserver.m
+++ src/OFStreamObserver.m
@@ -196,16 +196,11 @@
 		[queueFDs addItem: &fd];
 	} @finally {
 		[mutex unlock];
 	}
 
-#ifndef _WIN32
-	OF_ENSURE(write(cancelFD[1], "", 1) > 0);
-#else
-	OF_ENSURE(sendto(cancelFD[1], "", 1, 0, (struct sockaddr*)&cancelAddr,
-	    sizeof(cancelAddr)) > 0);
-#endif
+	[self cancel];
 }
 
 - (void)addStreamForWriting: (OFStream*)stream
 {
 	[mutex lock];
@@ -218,16 +213,11 @@
 		[queueFDs addItem: &fd];
 	} @finally {
 		[mutex unlock];
 	}
 
-#ifndef _WIN32
-	OF_ENSURE(write(cancelFD[1], "", 1) > 0);
-#else
-	OF_ENSURE(sendto(cancelFD[1], "", 1, 0, (struct sockaddr*)&cancelAddr,
-	    sizeof(cancelAddr)) > 0);
-#endif
+	[self cancel];
 }
 
 - (void)removeStreamForReading: (OFStream*)stream
 {
 	[mutex lock];
@@ -373,10 +363,20 @@
 - (BOOL)observeWithTimeout: (double)timeout
 {
 	@throw [OFNotImplementedException exceptionWithClass: [self class]
 						    selector: _cmd];
 }
+
+- (void)cancel
+{
+#ifndef _WIN32
+	OF_ENSURE(write(cancelFD[1], "", 1) > 0);
+#else
+	OF_ENSURE(sendto(cancelFD[1], "", 1, 0, (struct sockaddr*)&cancelAddr,
+	    sizeof(cancelAddr)) > 0);
+#endif
+}
 
 - (BOOL)_processCache
 {
 	OFStream **objects = [readStreams objects];
 	size_t i, count = [readStreams count];