fiber.cc revision 12920 
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#if HAVE_VALGRIND
33#include <valgrind/valgrind.h>
34#endif
35
36#include <cerrno>
37#include <cstring>
38
39#include "base/logging.hh"
40
41using namespace std;
42
43namespace
44{
45
46/*
47 * The PrimaryFiber class is a special case that attaches to the currently
48 * executing context. That makes handling the "primary" fiber, aka the one
49 * which most of gem5 is running under, no different than other Fibers.
50 */
51class PrimaryFiber : public Fiber
52{
53  public:
54    PrimaryFiber() : Fiber(nullptr, 0) { setStarted(); }
55    void main() { panic("PrimaryFiber main executed.\n"); }
56};
57
58PrimaryFiber _primaryFiber;
59
60// A pointer to whatever the currently executing Fiber is.
61Fiber *_currentFiber = &_primaryFiber;
62
63// A pointer to the Fiber which is currently being started/initialized.
64Fiber *startingFiber = nullptr;
65
66} // anonymous namespace
67
68void
69Fiber::entryTrampoline()
70{
71    startingFiber->start();
72}
73
74Fiber::Fiber(size_t stack_size) :
75    link(primaryFiber()),
76    stack(stack_size ? new uint8_t[stack_size] : nullptr),
77    stackSize(stack_size), started(false), _finished(false)
78{
79#if HAVE_VALGRIND
80    valgrindStackId = VALGRIND_STACK_REGISTER(stack, stack + stack_size);
81#endif
82}
83
84Fiber::Fiber(Fiber *link, size_t stack_size) :
85    link(link), stack(stack_size ? new uint8_t[stack_size] : nullptr),
86    stackSize(stack_size), started(false), _finished(false)
87{}
88
89Fiber::~Fiber()
90{
91    panic_if(stack && _currentFiber == this, "Fiber stack is in use.");
92#if HAVE_VALGRIND
93    VALGRIND_STACK_DEREGISTER(valgrindStackId);
94#endif
95    delete [] stack;
96}
97
98void
99Fiber::createContext()
100{
101    // Set up a context for the new fiber, starting it in the trampoline.
102    getcontext(&ctx);
103    ctx.uc_stack.ss_sp = stack;
104    ctx.uc_stack.ss_size = stackSize;
105    ctx.uc_link = nullptr;
106    makecontext(&ctx, &entryTrampoline, 0);
107
108    // Swap to the new context so it can enter its start() function. It
109    // will then swap itself back out and return here.
110    startingFiber = this;
111    panic_if(!_currentFiber, "No active Fiber object.");
112    swapcontext(&_currentFiber->ctx, &ctx);
113
114    // The new context is now ready and about to call main().
115}
116
117void
118Fiber::start()
119{
120    // Avoid a dangling pointer.
121    startingFiber = nullptr;
122
123    setStarted();
124
125    // Swap back to the parent context which is still considered "current",
126    // now that we're ready to go.
127    int ret M5_VAR_USED = swapcontext(&ctx, &_currentFiber->ctx);
128    panic_if(ret == -1, strerror(errno));
129
130    // Call main() when we're been reactivated for the first time.
131    main();
132
133    // main has returned, so this Fiber has finished. Switch to the "link"
134    // Fiber.
135    _finished = true;
136    link->run();
137}
138
139void
140Fiber::run()
141{
142    panic_if(_finished, "Fiber has already run to completion.");
143
144    // If we're already running this fiber, we're done.
145    if (_currentFiber == this)
146        return;
147
148    if (!started)
149        createContext();
150
151    // Switch out of the current Fiber's context and this one's in.
152    Fiber *prev = _currentFiber;
153    Fiber *next = this;
154    _currentFiber = next;
155    swapcontext(&prev->ctx, &next->ctx);
156}
157
158Fiber *Fiber::currentFiber() { return _currentFiber; }
159Fiber *Fiber::primaryFiber() { return &_primaryFiber; }
160