LibThread: Introduce a new threading library

This library is meant to provide C++-style wrappers over lower
level APIs such as syscalls and pthread_* functions, as well as
utilities for easily running pieces of logic on different
threads.

Applications/Makefile.common

@@ -3,7 +3,7 @@ DEFINES += -DUSERLAND
 all: $(APP)
 
 $(APP): $(OBJS)
-	$(LD) -o $(APP) $(LDFLAGS) $(OBJS) -lgui -ldraw -laudio -lipc -lvt -lpcidb -lcore -lc
+	$(LD) -o $(APP) $(LDFLAGS) $(OBJS) -lgui -ldraw -laudio -lipc -lthread -lvt -lpcidb -lcore -lc
 
 .cpp.o:
 	@echo "CXX $<"; $(CXX) $(CXXFLAGS) -o $@ -c $<

Kernel/makeall.sh

@@ -19,10 +19,11 @@ build_targets=""
 build_targets="$build_targets ../DevTools/IPCCompiler"
 build_targets="$build_targets ../DevTools/FormCompiler"
 
-# Build LibC, LibCore and LibIPC before IPC servers, since they depend on it.
+# Build LibC, LibCore, LibIPC and LibThread before IPC servers, since they depend on them.
 build_targets="$build_targets ../Libraries/LibC"
 build_targets="$build_targets ../Libraries/LibCore"
 build_targets="$build_targets ../Libraries/LibIPC"
+build_targets="$build_targets ../Libraries/LibThread"
 
 # Build IPC servers before their client code to ensure the IPC definitions are available.
 build_targets="$build_targets ../Servers/AudioServer"

Libraries/LibThread/BackgroundAction.cpp

@@ -0,0 +1,48 @@
+#include <LibThread/BackgroundAction.h>
+#include <LibThread/Thread.h>
+#include <LibCore/CLock.h>
+#include <AK/Queue.h>
+
+static CLockable<Queue<Function<void()>>>* s_all_actions;
+static LibThread::Thread* s_background_thread;
+
+static int background_thread_func()
+{
+    while (true) {
+        Function<void()> work_item;
+        {
+            LOCKER(s_all_actions->lock());
+
+            if (!s_all_actions->resource().is_empty())
+                work_item = s_all_actions->resource().dequeue();
+        }
+        if (work_item)
+            work_item();
+        else
+            sleep(1);
+    }
+
+    ASSERT_NOT_REACHED();
+}
+
+static void init()
+{
+    s_all_actions = new CLockable<Queue<Function<void()>>>();
+    s_background_thread = new LibThread::Thread(background_thread_func);
+    s_background_thread->set_name("Background thread");
+    s_background_thread->start();
+}
+
+CLockable<Queue<Function<void()>>>& LibThread::BackgroundActionBase::all_actions()
+{
+    if (s_all_actions == nullptr)
+        init();
+    return *s_all_actions;
+}
+
+LibThread::Thread& LibThread::BackgroundActionBase::background_thread()
+{
+    if (s_background_thread == nullptr)
+        init();
+    return *s_background_thread;
+}

Libraries/LibThread/BackgroundAction.h

@@ -0,0 +1,75 @@
+#pragma once
+
+#include <AK/Function.h>
+#include <AK/NonnullRefPtr.h>
+#include <AK/Optional.h>
+#include <AK/Queue.h>
+#include <AK/RefCounted.h>
+#include <LibCore/CEventLoop.h>
+#include <LibCore/CLock.h>
+#include <LibCore/CObject.h>
+#include <LibThread/Thread.h>
+
+namespace LibThread {
+
+template<typename Result>
+class BackgroundAction;
+
+class BackgroundActionBase {
+    template<typename Result>
+    friend class BackgroundAction;
+
+private:
+    BackgroundActionBase() {}
+
+    static CLockable<Queue<Function<void()>>>& all_actions();
+    static Thread& background_thread();
+};
+
+template<typename Result>
+class BackgroundAction final : public CObject
+    , public RefCounted<BackgroundAction<Result>>
+    , private BackgroundActionBase {
+
+    C_OBJECT(BackgroundAction);
+
+public:
+    static NonnullRefPtr<BackgroundAction<Result>> create(
+        Function<Result()> action,
+        Function<void(Result)> on_complete = nullptr
+    )
+    {
+        return adopt(*new BackgroundAction(move(action), move(on_complete)));
+    }
+
+    virtual ~BackgroundAction() {}
+
+private:
+
+    BackgroundAction(Function<Result()> action, Function<void(Result)> on_complete)
+        : CObject(background_thread())
+        , m_action(move(action))
+        , m_on_complete(move(on_complete))
+    {
+        LOCKER(all_actions().lock());
+
+        this->ref();
+        all_actions().resource().enqueue([this] {
+            m_result = m_action();
+            if (m_on_complete) {
+                CEventLoop::main().post_event(*this, make<CDeferredInvocationEvent>([this](CObject&) {
+                    m_on_complete(m_result.release_value());
+                    this->deref();
+                }));
+                CEventLoop::main().wake();
+            } else
+                this->deref();
+        });
+    }
+
+    Function<Result()> m_action;
+    Function<void(Result)> m_on_complete;
+    Optional<Result> m_result;
+};
+
+}

Libraries/LibThread/Makefile

@@ -0,0 +1,21 @@
+include ../../Makefile.common
+
+OBJS = \
+    Thread.o \
+    BackgroundAction.o
+
+LIBRARY = libthread.a
+DEFINES += -DUSERLAND
+
+all: $(LIBRARY)
+
+$(LIBRARY): $(OBJS)
+	@echo "LIB $@"; $(AR) rcs $@ $(OBJS) $(LIBS)
+
+.cpp.o:
+	@echo "CXX $<"; $(CXX) $(CXXFLAGS) -o $@ -c $<
+
+-include $(OBJS:%.o=%.d)
+
+clean:
+	@echo "CLEAN"; rm -f $(LIBRARY) $(OBJS) *.d

Libraries/LibThread/Thread.cpp

@@ -0,0 +1,39 @@
+#include <LibThread/Thread.h>
+#include <unistd.h>
+
+LibThread::Thread::Thread(Function<int()> action)
+    : CObject(nullptr)
+    , m_action(move(action))
+{
+}
+
+LibThread::Thread::~Thread()
+{
+    if (m_tid != -1) {
+        dbg() << "trying to destroy a running thread!";
+        ASSERT_NOT_REACHED();
+    }
+}
+
+void LibThread::Thread::start()
+{
+    int rc = create_thread([](void* arg) {
+        Thread* self = static_cast<Thread*>(arg);
+        int exit_code = self->m_action();
+        self->m_tid = -1;
+        exit_thread(exit_code);
+        return exit_code;
+    }, static_cast<void*>(this));
+
+    ASSERT(rc > 0);
+    dbg() << "Started a thread, tid = " << rc;
+    m_tid = rc;
+}
+
+void LibThread::Thread::quit(int code)
+{
+    ASSERT(m_tid == gettid());
+
+    m_tid = -1;
+    exit_thread(code);
+}

Libraries/LibThread/Thread.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include <AK/Function.h>
+#include <LibCore/CObject.h>
+
+namespace LibThread {
+
+class Thread final : public CObject {
+    C_OBJECT(Thread);
+
+public:
+    explicit Thread(Function<int()> action);
+    virtual ~Thread();
+
+    void start();
+    void quit(int code = 0);
+
+private:
+    Function<int()> m_action;
+    int m_tid { -1 };
+};
+
+}

Makefile.common

@@ -22,6 +22,7 @@ LDFLAGS = \
     -L$(SERENITY_BASE_DIR)/Libraries/LibM \
     -L$(SERENITY_BASE_DIR)/Libraries/LibDraw \
     -L$(SERENITY_BASE_DIR)/Libraries/LibGUI \
+    -L$(SERENITY_BASE_DIR)/Libraries/LibThread \
     -L$(SERENITY_BASE_DIR)/Libraries/LibVT \
     -L$(SERENITY_BASE_DIR)/Libraries/LibAudio
 

Userland/Makefile

@@ -19,7 +19,7 @@ clean:
 
 $(APPS) : % : %.o $(OBJS)
 	@echo "LD $@"
-	@$(LD) -o $@ $(LDFLAGS) $< -lc -lgui -ldraw -laudio -lipc -lcore -lpcidb
+	@$(LD) -o $@ $(LDFLAGS) $< -lc -lgui -ldraw -laudio -lipc -lthread -lcore -lpcidb
 
 %.o: %.cpp
 	@echo "CXX $<"