fiber.cc revision 12787 
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#include "base/fiber.hh"
31
32#include <cerrno>
33#include <cstring>
34
35#include "base/logging.hh"
36
37using namespace std;
38
39namespace
40{
41
42/*
43 * The PrimaryFiber class is a special case that attaches to the currently
44 * executing context. That makes handling the "primary" fiber, aka the one
45 * which most of gem5 is running under, no different than other Fibers.
46 */
47class PrimaryFiber : public Fiber
48{
49  public:
50    PrimaryFiber() : Fiber(nullptr, 0) { setStarted(); }
51    void main() { panic("PrimaryFiber main executed.\n"); }
52};
53
54PrimaryFiber _primaryFiber;
55
56// A pointer to whatever the currently executing Fiber is.
57Fiber *_currentFiber = &_primaryFiber;
58
59// A pointer to the Fiber which is currently being started/initialized.
60Fiber *startingFiber = nullptr;
61
62} // anonymous namespace
63
64void
65Fiber::entryTrampoline()
66{
67    startingFiber->start();
68}
69
70Fiber::Fiber(size_t stack_size) :
71    link(primaryFiber()),
72    stack(stack_size ? new uint8_t[stack_size] : nullptr),
73    stackSize(stack_size), started(false), _finished(false)
74{}
75
76Fiber::Fiber(Fiber *link, size_t stack_size) :
77    link(link), stack(stack_size ? new uint8_t[stack_size] : nullptr),
78    stackSize(stack_size), started(false), _finished(false)
79{}
80
81Fiber::~Fiber()
82{
83    panic_if(stack && _currentFiber == this, "Fiber stack is in use.");
84    delete [] stack;
85}
86
87void
88Fiber::createContext()
89{
90    // Set up a context for the new fiber, starting it in the trampoline.
91    getcontext(&ctx);
92    ctx.uc_stack.ss_sp = stack;
93    ctx.uc_stack.ss_size = stackSize;
94    ctx.uc_link = nullptr;
95    makecontext(&ctx, &entryTrampoline, 0);
96
97    // Swap to the new context so it can enter its start() function. It
98    // will then swap itself back out and return here.
99    startingFiber = this;
100    panic_if(!_currentFiber, "No active Fiber object.");
101    swapcontext(&_currentFiber->ctx, &ctx);
102
103    // The new context is now ready and about to call main().
104}
105
106void
107Fiber::start()
108{
109    // Avoid a dangling pointer.
110    startingFiber = nullptr;
111
112    setStarted();
113
114    // Swap back to the parent context which is still considered "current",
115    // now that we're ready to go.
116    int ret M5_VAR_USED = swapcontext(&ctx, &_currentFiber->ctx);
117    panic_if(ret == -1, strerror(errno));
118
119    // Call main() when we're been reactivated for the first time.
120    main();
121
122    // main has returned, so this Fiber has finished. Switch to the "link"
123    // Fiber.
124    _finished = true;
125    link->run();
126}
127
128void
129Fiber::run()
130{
131    panic_if(_finished, "Fiber has already run to completion.");
132
133    // If we're already running this fiber, we're done.
134    if (_currentFiber == this)
135        return;
136
137    if (!started)
138        createContext();
139
140    // Switch out of the current Fiber's context and this one's in.
141    Fiber *prev = _currentFiber;
142    Fiber *next = this;
143    _currentFiber = next;
144    swapcontext(&prev->ctx, &next->ctx);
145}
146
147Fiber *Fiber::currentFiber() { return _currentFiber; }
148Fiber *Fiber::primaryFiber() { return &_primaryFiber; }
149