fiber.hh revision 12787:1f6e23cddf71 
1/*
2 * Copyright 2018 Google, Inc.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions are
6 * met: redistributions of source code must retain the above copyright
7 * notice, this list of conditions and the following disclaimer;
8 * redistributions in binary form must reproduce the above copyright
9 * notice, this list of conditions and the following disclaimer in the
10 * documentation and/or other materials provided with the distribution;
11 * neither the name of the copyright holders nor the names of its
12 * contributors may be used to endorse or promote products derived from
13 * this software without specific prior written permission.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
18 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
19 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
20 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
21 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
25 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 *
27 * Authors: Gabe Black
28 */
29
30#ifndef __BASE_FIBER_HH__
31#define __BASE_FIBER_HH__
32
33#include <ucontext.h>
34
35#include <cstddef>
36#include <cstdint>
37
38/**
39 * This class represents a fiber, which is a light weight sort of thread which
40 * is cooperatively scheduled and runs sequentially with other fibers, swapping
41 * in and out of a single actual thread of execution.
42 *
43 * To define your own threads, create a subclass of Fiber and override its
44 * main() function to do what you want your fiber to do. You can start it by
45 * calling its run() method which will stop your execution and start the other
46 * fiber in your place.
47 *
48 * If your main() function ends, that fiber will automatically switch to either
49 * the primary fiber, or to a particular fiber you specified at construction
50 * time, and your fiber is considered finished.
51 */
52
53class Fiber
54{
55  public:
56    const static size_t DefaultStackSize = 0x50000;
57
58    /// stack_size is the size of the stack available to this fiber.
59    /// link points to another fiber which will start executing when this
60    /// fiber's main function returns.
61    Fiber(size_t stack_size=DefaultStackSize);
62    Fiber(Fiber *link, size_t stack_size=DefaultStackSize);
63
64    virtual ~Fiber();
65
66    /// Start executing the fiber represented by this object. This function
67    /// will "return" when the current fiber is switched back to later on.
68    void run();
69
70    /// Returns whether the "main" function of this fiber has finished.
71    ///
72    bool finished() const { return _finished; };
73
74    /// Get a pointer to the current running Fiber.
75    ///
76    static Fiber *currentFiber();
77    /// Get a pointer to the primary Fiber.
78    /// This Fiber represents the thread of execution started by the OS, and
79    /// which has a Fiber attached to it after the fact.
80    static Fiber *primaryFiber();
81
82  protected:
83    /// This method is called when this fiber is first run. Override it to
84    /// give your fiber something to do. When main returns, the fiber will
85    /// mark itself as finished and switch to its link fiber.
86    virtual void main() = 0;
87
88    void setStarted() { started = true; }
89
90  private:
91    static void entryTrampoline();
92    void start();
93
94    ucontext_t ctx;
95    Fiber *link;
96
97    // The stack for this context, or a nullptr if allocated elsewhere.
98    uint8_t *stack;
99    size_t stackSize;
100
101    bool started;
102    bool _finished;
103    void createContext();
104};
105
106#endif // __BASE_FIBER_HH__
107