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Diffstat (limited to 'src/base/fiber.cc')
-rw-r--r-- | src/base/fiber.cc | 148 |
1 files changed, 148 insertions, 0 deletions
diff --git a/src/base/fiber.cc b/src/base/fiber.cc new file mode 100644 index 000000000..f10f1fbfd --- /dev/null +++ b/src/base/fiber.cc @@ -0,0 +1,148 @@ +/* + * 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 + */ + +#include "base/fiber.hh" + +#include <cerrno> +#include <cstring> + +#include "base/logging.hh" + +using namespace std; + +namespace +{ + +/* + * The PrimaryFiber class is a special case that attaches to the currently + * executing context. That makes handling the "primary" fiber, aka the one + * which most of gem5 is running under, no different than other Fibers. + */ +class PrimaryFiber : public Fiber +{ + public: + PrimaryFiber() : Fiber(nullptr, 0) { setStarted(); } + void main() { panic("PrimaryFiber main executed.\n"); } +}; + +PrimaryFiber _primaryFiber; + +// A pointer to whatever the currently executing Fiber is. +Fiber *_currentFiber = &_primaryFiber; + +// A pointer to the Fiber which is currently being started/initialized. +Fiber *startingFiber = nullptr; + +} // anonymous namespace + +void +Fiber::entryTrampoline() +{ + startingFiber->start(); +} + +Fiber::Fiber(size_t stack_size) : + link(primaryFiber()), + stack(stack_size ? new uint8_t[stack_size] : nullptr), + stackSize(stack_size), started(false), _finished(false) +{} + +Fiber::Fiber(Fiber *link, size_t stack_size) : + link(link), stack(stack_size ? new uint8_t[stack_size] : nullptr), + stackSize(stack_size), started(false), _finished(false) +{} + +Fiber::~Fiber() +{ + panic_if(stack && _currentFiber == this, "Fiber stack is in use."); + delete [] stack; +} + +void +Fiber::createContext() +{ + // Set up a context for the new fiber, starting it in the trampoline. + getcontext(&ctx); + ctx.uc_stack.ss_sp = stack; + ctx.uc_stack.ss_size = stackSize; + ctx.uc_link = nullptr; + makecontext(&ctx, &entryTrampoline, 0); + + // Swap to the new context so it can enter its start() function. It + // will then swap itself back out and return here. + startingFiber = this; + panic_if(!_currentFiber, "No active Fiber object."); + swapcontext(&_currentFiber->ctx, &ctx); + + // The new context is now ready and about to call main(). +} + +void +Fiber::start() +{ + // Avoid a dangling pointer. + startingFiber = nullptr; + + setStarted(); + + // Swap back to the parent context which is still considered "current", + // now that we're ready to go. + int ret M5_VAR_USED = swapcontext(&ctx, &_currentFiber->ctx); + panic_if(ret == -1, strerror(errno)); + + // Call main() when we're been reactivated for the first time. + main(); + + // main has returned, so this Fiber has finished. Switch to the "link" + // Fiber. + _finished = true; + link->run(); +} + +void +Fiber::run() +{ + panic_if(_finished, "Fiber has already run to completion."); + + // If we're already running this fiber, we're done. + if (_currentFiber == this) + return; + + if (!started) + createContext(); + + // Switch out of the current Fiber's context and this one's in. + Fiber *prev = _currentFiber; + Fiber *next = this; + _currentFiber = next; + swapcontext(&prev->ctx, &next->ctx); +} + +Fiber *Fiber::currentFiber() { return _currentFiber; } +Fiber *Fiber::primaryFiber() { return &_primaryFiber; } |