kernel/vm: DaemonCondition is really just a basic binary semaphore.

So split it off into its own file. This will make it easier to
split the page writer off into a separate file.

headers/private/kernel/util/BinarySemaphore.h

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2010, Ingo Weinhold, [email protected].
+ * Copyright 2026, Haiku, Inc. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef KERNEL_UTIL_BINARY_SEMAPHORE_H
+#define KERNEL_UTIL_BINARY_SEMAPHORE_H
+
+
+#include <condition_variable.h>
+#include <util/AutoLock.h>
+
+
+struct BinarySemaphore {
+	void Init(const char* name)
+	{
+		mutex_init(&fLock, "binary semaphore");
+		fCondition.Init(this, name);
+		fActivated = false;
+	}
+
+	bool Lock()
+	{
+		return mutex_lock(&fLock) == B_OK;
+	}
+
+	void Unlock()
+	{
+		mutex_unlock(&fLock);
+	}
+
+	bool Wait(bigtime_t timeout, bool clearActivated)
+	{
+		MutexLocker locker(fLock);
+		if (clearActivated)
+			fActivated = false;
+		else if (fActivated)
+			return true;
+
+		ConditionVariableEntry entry;
+		fCondition.Add(&entry);
+
+		locker.Unlock();
+
+		return entry.Wait(B_RELATIVE_TIMEOUT, timeout) == B_OK;
+	}
+
+	void WakeUp()
+	{
+		if (fActivated)
+			return;
+
+		MutexLocker locker(fLock);
+		fActivated = true;
+		fCondition.NotifyOne();
+	}
+
+	void ClearActivated()
+	{
+		MutexLocker locker(fLock);
+		fActivated = false;
+	}
+
+private:
+	mutex				fLock;
+	ConditionVariable	fCondition;
+	bool				fActivated;
+};
+
+
+#endif	// KERNEL_UTIL_BINARY_SEMAPHORE_H