ProcessManager: Add a process-specific tab view below the process table.

To start out, add a "Stacks" view where we see what the selected process is
currently doing (via /proc/PID/stack) :^)

Applications/ProcessManager/Makefile

@@ -5,6 +5,7 @@ OBJS = \
     ProcessTableView.o \
     MemoryStatsWidget.o \
     GraphWidget.o \
+    ProcessStacksWidget.o \
     main.o
 
 APP = ProcessManager

Applications/ProcessManager/ProcessStacksWidget.cpp

@@ -0,0 +1,38 @@
+#include "ProcessStacksWidget.h"
+#include <LibCore/CFile.h>
+#include <LibCore/CTimer.h>
+#include <LibGUI/GBoxLayout.h>
+
+ProcessStacksWidget::ProcessStacksWidget(GWidget* parent)
+    : GWidget(parent)
+{
+    set_layout(make<GBoxLayout>(Orientation::Vertical));
+    layout()->set_margins({ 4, 4, 4, 4 });
+    m_stacks_editor = new GTextEditor(GTextEditor::Type::MultiLine, this);
+    m_stacks_editor->set_readonly(true);
+
+    m_timer = new CTimer(1000, [this] { refresh(); });
+}
+
+ProcessStacksWidget::~ProcessStacksWidget()
+{
+}
+
+void ProcessStacksWidget::set_pid(pid_t pid)
+{
+    if (m_pid == pid)
+        return;
+    m_pid = pid;
+    refresh();
+}
+
+void ProcessStacksWidget::refresh()
+{
+    CFile file(String::format("/proc/%d/stack", m_pid));
+    if (!file.open(CIODevice::ReadOnly)) {
+        m_stacks_editor->set_text(String::format("Unable to open %s", file.filename().characters()));
+        return;
+    }
+
+    m_stacks_editor->set_text(file.read_all());
+}

Applications/ProcessManager/ProcessStacksWidget.h

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <LibGUI/GTextEditor.h>
+#include <LibGUI/GWidget.h>
+
+class CTimer;
+
+class ProcessStacksWidget final : public GWidget {
+    C_OBJECT(ProcessStacksWidget)
+public:
+    explicit ProcessStacksWidget(GWidget* parent);
+    virtual ~ProcessStacksWidget() override;
+
+    void set_pid(pid_t);
+    void refresh();
+
+private:
+    pid_t m_pid { -1 };
+    GTextEditor* m_stacks_editor { nullptr };
+    CTimer* m_timer { nullptr };
+};

Applications/ProcessManager/main.cpp

@@ -1,5 +1,6 @@
 #include "GraphWidget.h"
 #include "MemoryStatsWidget.h"
+#include "ProcessStacksWidget.h"
 #include "ProcessTableView.h"
 #include <LibCore/CTimer.h>
 #include <LibGUI/GAction.h>
@@ -8,6 +9,7 @@
 #include <LibGUI/GGroupBox.h>
 #include <LibGUI/GLabel.h>
 #include <LibGUI/GMenuBar.h>
+#include <LibGUI/GSplitter.h>
 #include <LibGUI/GTabWidget.h>
 #include <LibGUI/GToolBar.h>
 #include <LibGUI/GWidget.h>
@@ -26,7 +28,9 @@ int main(int argc, char** argv)
     keeper->set_background_color(Color::WarmGray);
     keeper->layout()->set_margins({ 4, 4, 4, 4 });
 
-    auto* tabwidget = new GTabWidget(keeper);
+    auto* splitter = new GSplitter(Orientation::Vertical, keeper);
+
+    auto* tabwidget = new GTabWidget(splitter);
 
     auto* process_table_container = new GWidget(nullptr);
     tabwidget->add_widget("Processes", process_table_container);
@@ -149,6 +153,14 @@ int main(int argc, char** argv)
 
     app.set_menubar(move(menubar));
 
+    auto* process_tab_widget = new GTabWidget(splitter);
+    auto* stacks_widget = new ProcessStacksWidget(nullptr);
+    process_tab_widget->add_widget("Stacks", stacks_widget);
+
+    process_table_view->on_process_selected = [&](pid_t pid) {
+        stacks_widget->set_pid(pid);
+    };
+
     auto* window = new GWindow;
     window->set_title("Process Manager");
     window->set_rect(20, 200, 680, 400);