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+/*
+ * Copyright 2018 Google, Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Gabe Black
+ */
+
+#ifndef __BASE_FIBER_HH__
+#define __BASE_FIBER_HH__
+
+#include <ucontext.h>
+
+#include <cstddef>
+#include <cstdint>
+
+/**
+ * This class represents a fiber, which is a light weight sort of thread which
+ * is cooperatively scheduled and runs sequentially with other fibers, swapping
+ * in and out of a single actual thread of execution.
+ *
+ * To define your own threads, create a subclass of Fiber and override its
+ * main() function to do what you want your fiber to do. You can start it by
+ * calling its run() method which will stop your execution and start the other
+ * fiber in your place.
+ *
+ * If your main() function ends, that fiber will automatically switch to either
+ * the primary fiber, or to a particular fiber you specified at construction
+ * time, and your fiber is considered finished.
+ */
+
+class Fiber
+{
+  public:
+    const static size_t DefaultStackSize = 0x50000;
+
+    /// stack_size is the size of the stack available to this fiber.
+    /// link points to another fiber which will start executing when this
+    /// fiber's main function returns.
+    Fiber(size_t stack_size=DefaultStackSize);
+    Fiber(Fiber *link, size_t stack_size=DefaultStackSize);
+
+    virtual ~Fiber();
+
+    /// Start executing the fiber represented by this object. This function
+    /// will "return" when the current fiber is switched back to later on.
+    void run();
+
+    /// Returns whether the "main" function of this fiber has finished.
+    ///
+    bool finished() const { return _finished; };
+
+    /// Get a pointer to the current running Fiber.
+    ///
+    static Fiber *currentFiber();
+    /// Get a pointer to the primary Fiber.
+    /// This Fiber represents the thread of execution started by the OS, and
+    /// which has a Fiber attached to it after the fact.
+    static Fiber *primaryFiber();
+
+  protected:
+    /// This method is called when this fiber is first run. Override it to
+    /// give your fiber something to do. When main returns, the fiber will
+    /// mark itself as finished and switch to its link fiber.
+    virtual void main() = 0;
+
+    void setStarted() { started = true; }
+
+  private:
+    static void entryTrampoline();
+    void start();
+
+    ucontext_t ctx;
+    Fiber *link;
+
+    // The stack for this context, or a nullptr if allocated elsewhere.
+    uint8_t *stack;
+    size_t stackSize;
+
+    bool started;
+    bool _finished;
+    void createContext();
+};
+
+#endif // __BASE_FIBER_HH__