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fibers.cc
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540
#include "coroutine.h"
#include <assert.h>
#include <node/node.h>
#include <vector>
#include <iostream>
#define THROW(x, m) return ThrowException(x(String::New(m)))
#ifdef DEBUG
// Run GC more often when debugging
#define GC_ADJUST 100
#else
#define GC_ADJUST 1
#endif
using namespace std;
using namespace v8;
class Fiber {
#define Unwrap(target, handle) \
assert(!handle.IsEmpty()); \
assert(handle->InternalFieldCount() == 1); \
target = *static_cast<Fiber*>(handle->GetPointerFromInternalField(0));
private:
static Locker* global_locker; // Node does not use locks or threads, so we need a global lock
static Persistent<FunctionTemplate> tmpl;
static Persistent<Function> fiber_object;
static Fiber* current;
static vector<Fiber*> orphaned_fibers;
static Persistent<Value> fatal_stack;
Persistent<Object> handle;
Persistent<Function> cb;
Persistent<Context> v8_context;
Persistent<Value> zombie_exception;
Persistent<Value> yielded;
Isolate* isolate;
bool yielded_exception;
Coroutine* entry_fiber;
Coroutine* this_fiber;
bool started;
bool yielding;
bool zombie;
bool resetting;
Fiber(Handle<Object> handle, Handle<Function> cb, Handle<Context> v8_context) :
handle(Persistent<Object>::New(handle)),
cb(Persistent<Function>::New(cb)),
v8_context(Persistent<Context>::New(v8_context)),
isolate(Isolate::GetCurrent()),
started(false),
yielding(false),
zombie(false),
resetting(false) {
MakeWeak();
handle->SetPointerInInternalField(0, this);
}
virtual ~Fiber() {
assert(!this->started);
handle.Dispose();
cb.Dispose();
v8_context.Dispose();
}
/**
* Call MakeWeak if it's ok for v8 to garbage collect this Fiber.
* i.e. After fiber completes, while yielded, or before started
*/
void MakeWeak() {
handle.MakeWeak(this, WeakCallback);
}
/**
* And call ClearWeak if it's not ok for v8 to garbage collect this Fiber.
* i.e. While running.
*/
void ClearWeak() {
handle.ClearWeak();
}
/**
* Called when there are no more references to this object in Javascript. If this happens and
* the fiber is currently suspended we'll unwind the fiber's stack by throwing exceptions in
* order to clear all references.
*/
static void WeakCallback(Persistent<Value> value, void* data) {
Fiber& that = *static_cast<Fiber*>(data);
assert(that.handle == value);
assert(value.IsNearDeath());
assert(current != &that);
// We'll unwind running fibers later... doing it from the garbage collector is bad news.
if (that.started) {
assert(that.yielding);
orphaned_fibers.push_back(&that);
that.ClearWeak();
return;
}
delete &that;
}
/**
* When the v8 garbage collector notifies us about dying fibers instead of unwindng their
* stack as soon as possible we put them aside to unwind later. Unwinding from the garbage
* collector leads to exponential time garbage collections if there are many orphaned Fibers,
* there's also the possibility of running out of stack space. It's generally bad news.
*
* So instead we have this function to clean up all the fibers after the garbage collection
* has finished.
*/
static void DestroyOrphans() {
if (orphaned_fibers.empty()) {
return;
}
vector<Fiber*> orphans(orphaned_fibers);
orphaned_fibers.clear();
for (vector<Fiber*>::iterator ii = orphans.begin(); ii != orphans.end(); ++ii) {
Fiber& that = **ii;
that.UnwindStack();
if (that.yielded_exception) {
// If you throw an exception from a fiber that's being garbage collected there's no way
// to bubble that exception up to the application.
String::Utf8Value stack(fatal_stack);
cerr <<
"An exception was thrown from a Fiber which was being garbage collected. This error "
"can not be gracefully recovered from. The only acceptable behavior is to terminate "
"this application. The exception appears below:\n\n"
<<*stack <<"\n";
exit(1);
} else {
fatal_stack.Dispose();
}
that.yielded.Dispose();
that.MakeWeak();
}
}
/**
* Instantiate a new Fiber object. When a fiber is created it only grabs a handle to the
* callback; it doesn't create any new contexts until run() is called.
*/
static Handle<Value> New(const Arguments& args) {
if (args.Length() != 1) {
THROW(Exception::TypeError, "Fiber expects 1 argument");
} else if (!args[0]->IsFunction()) {
THROW(Exception::TypeError, "Fiber expects a function");
} else if (!args.IsConstructCall()) {
Handle<Value> argv[1] = { args[0] };
return tmpl->GetFunction()->NewInstance(1, argv);
}
Handle<Function> fn = Handle<Function>::Cast(args[0]);
new Fiber(args.This(), fn, Context::GetCurrent());
return args.This();
}
/**
* Begin or resume the current fiber. If the fiber is not currently running a new context will
* be created and the callback will start. Otherwise we switch back into the exist context.
*/
static Handle<Value> Run(const Arguments& args) {
Unwrap(Fiber& that, args.Holder());
// There seems to be no better place to put this check..
DestroyOrphans();
if (that.started && !that.yielding) {
THROW(Exception::Error, "This Fiber is already running");
} else if (args.Length() > 1) {
THROW(Exception::TypeError, "run() excepts 1 or no arguments");
}
if (!that.started) {
// Create a new context with entry point `Fiber::RunFiber()`.
that.started = true;
void** data = new void*[2];
data[0] = (void*)&args;
data[1] = &that;
that.this_fiber = &Coroutine::create_fiber((void (*)(void*))RunFiber, data);
V8::AdjustAmountOfExternalAllocatedMemory(that.this_fiber->size() * GC_ADJUST);
} else {
// If the fiber is currently running put the first parameter to `run()` on `yielded`, then
// the pending call to `yield()` will return that value. `yielded` in this case is just a
// misnomer, we're just reusing the same handle.
that.yielded_exception = false;
if (args.Length()) {
that.yielded = Persistent<Value>::New(args[0]);
} else {
that.yielded = Persistent<Value>::New(Undefined());
}
}
that.SwapContext();
return that.ReturnYielded();
}
/**
* Throw an exception into a currently yielding fiber.
*/
static Handle<Value> ThrowInto(const Arguments& args) {
Unwrap(Fiber& that, args.Holder());
if (!that.yielding) {
THROW(Exception::Error, "This Fiber is not yielding");
} else if (args.Length() == 0) {
that.yielded = Persistent<Value>::New(Undefined());
} else if (args.Length() == 1) {
that.yielded = Persistent<Value>::New(args[0]);
} else {
THROW(Exception::TypeError, "throwInto() expects 1 or no arguments");
}
that.yielded_exception = true;
that.SwapContext();
return that.ReturnYielded();
}
/**
* Unwinds a currently running fiber. If the fiber is not running then this function has no
* effect.
*/
static Handle<Value> Reset(const Arguments& args) {
Unwrap(Fiber& that, args.Holder());
if (!that.started) {
return Undefined();
} else if (!that.yielding) {
THROW(Exception::Error, "This Fiber is not yielding");
} else if (args.Length()) {
THROW(Exception::TypeError, "reset() expects no arguments");
}
that.resetting = true;
that.UnwindStack();
that.resetting = false;
that.MakeWeak();
Handle<Value> val = that.yielded;
that.yielded.Dispose();
if (that.yielded_exception) {
return ThrowException(val);
} else {
return val;
}
}
/**
* Turns the fiber into a zombie and unwinds its whole stack.
*
* After calling this function you must either destroy this fiber or call MakeWeak() or it will
* be leaked.
*/
void UnwindStack() {
assert(!zombie);
assert(started);
assert(yielding);
zombie = true;
// Setup an exception which will be thrown and rethrown from Fiber::Yield()
Local<Value> zombie_exception = Exception::Error(String::New("This Fiber is a zombie"));
this->zombie_exception = Persistent<Value>::New(zombie_exception);
yielded = Persistent<Value>::New(zombie_exception);
yielded_exception = true;
// Swap context back to Fiber::Yield() which will throw an exception to unwind the stack.
// Futher calls to yield from this fiber will rethrow the same exception.
SwapContext();
assert(!started);
zombie = false;
// Make sure this is the exception we threw
if (yielded_exception && yielded == zombie_exception) {
yielded_exception = false;
yielded.Dispose();
yielded = Persistent<Value>::New(Undefined());
}
this->zombie_exception.Dispose();
}
/**
* Common logic between Run(), ThrowInto(), and UnwindStack(). This is essentially just a
* wrapper around this->fiber->() which also handles all the bookkeeping needed.
*/
void SwapContext() {
entry_fiber = &Coroutine::current();
Fiber* last_fiber = current;
current = this;
// This will jump into either `RunFiber()` or `Yield()`, depending on if the fiber was
// already running.
{
Unlocker unlocker(isolate);
this_fiber->run();
}
// At this point the fiber either returned or called `yield()`.
current = last_fiber;
}
/**
* Grabs and resets this fiber's yielded value.
*/
Handle<Value> ReturnYielded() {
Handle<Value> val = yielded;
yielded.Dispose();
if (yielded_exception) {
return ThrowException(val);
} else {
return val;
}
}
/**
* This is the entry point for a new fiber, from `run()`.
*/
static void RunFiber(void** data) {
const Arguments* args = (const Arguments*)data[0];
Fiber& that = *(Fiber*)data[1];
delete[] data;
// New C scope so that the stack-allocated objects will be destroyed before calling
// Coroutine::finish, because that function may not return, in which case the destructors in
// this function won't be called.
{
Locker locker(that.isolate);
Isolate::Scope isolate_scope(that.isolate);
HandleScope scope;
// Set the stack guard for this "thread"; allow 2k of padding past the JS limit for C++ code
// to run
ResourceConstraints constraints;
constraints.set_stack_limit(reinterpret_cast<uint32_t*>(
(char*)that.this_fiber->bottom() + 2 * 1024));
SetResourceConstraints(&constraints);
TryCatch try_catch;
that.ClearWeak();
that.v8_context->Enter();
// Workaround for v8 issue #1180
// http://code.google.com/p/v8/issues/detail?id=1180
Script::Compile(String::New("void 0;"));
Handle<Value> yielded;
if (args->Length()) {
Handle<Value> argv[1] = { (*args)[0] };
yielded = that.cb->Call(that.v8_context->Global(), 1, argv);
} else {
yielded = that.cb->Call(that.v8_context->Global(), 0, NULL);
}
if (try_catch.HasCaught()) {
that.yielded = Persistent<Value>::New(try_catch.Exception());
that.yielded_exception = true;
if (that.zombie && !that.resetting && that.yielded != that.zombie_exception) {
// Throwing an exception from a garbage sweep
fatal_stack = Persistent<Value>::New(try_catch.StackTrace());
}
} else {
that.yielded = Persistent<Value>::New(yielded);
that.yielded_exception = false;
}
// Do not invoke the garbage collector if there's no context on the stack. It will seg fault
// otherwise.
V8::AdjustAmountOfExternalAllocatedMemory(-that.this_fiber->size() * GC_ADJUST);
// Don't make weak until after notifying the garbage collector. Otherwise it may try and
// free this very fiber!
if (!that.zombie) {
that.MakeWeak();
}
// Now safe to leave the context, this stack is done with JS.
that.v8_context->Exit();
}
// The function returned (instead of yielding).
that.started = false;
that.this_fiber->finish(*that.entry_fiber);
}
/**
* Yield control back to the function that called `run()`. The first parameter to this function
* is returned from `run()`. The context is saved, to be later resumed from `run()`.
*/
static Handle<Value> Yield(const Arguments& args) {
if (current == NULL) {
THROW(Exception::Error, "yield() called with no fiber running");
}
Fiber& that = *current;
if (that.zombie) {
return ThrowException(that.zombie_exception);
} else if (args.Length() == 0) {
that.yielded = Persistent<Value>::New(Undefined());
} else if (args.Length() == 1) {
that.yielded = Persistent<Value>::New(args[0]);
} else {
THROW(Exception::TypeError, "yield() expects 1 or no arguments");
}
that.yielded_exception = false;
// While not running this can be garbage collected if no one has a handle.
that.MakeWeak();
// Return control back to `Fiber::run()`. While control is outside this function we mark it as
// ok to garbage collect. If no one ever has a handle to resume the function it's harmful to
// keep the handle around.
{
Unlocker unlocker(that.isolate);
that.yielding = true;
that.entry_fiber->run();
that.yielding = false;
}
// Now `run()` has been called again.
// Don't garbage collect anymore!
that.ClearWeak();
// Return the yielded value
return that.ReturnYielded();
}
/**
* Getters for `started`, and `current`.
*/
static Handle<Value> GetStarted(Local<String> property, const AccessorInfo& info) {
if (info.This().IsEmpty() || info.This()->InternalFieldCount() != 1) {
return Undefined();
}
Unwrap(Fiber& that, info.This());
return Boolean::New(that.started);
}
static Handle<Value> GetCurrent(Local<String> property, const AccessorInfo& info) {
if (current) {
return current->handle;
} else {
return Undefined();
}
}
/**
* Allow access to coroutine pool size
*/
static Handle<Value> GetPoolSize(Local<String> property, const AccessorInfo& info) {
return Number::New(Coroutine::pool_size);
}
static void SetPoolSize(Local<String> property, Local<Value> value, const AccessorInfo& info) {
Coroutine::pool_size = value->ToNumber()->Value();
}
/**
* Return number of fibers that have been created
*/
static Handle<Value> GetFibersCreated(Local<String> property, const AccessorInfo& info) {
return Number::New(Coroutine::coroutines_created());
}
public:
/**
* Initialize the Fiber library.
*/
static void Init(Handle<Object> target) {
// Use a locker which won't get destroyed when this library gets unloaded. This is a hack
// to prevent v8 from trying to clean up this "thread" while the whole application is
// shutting down. TODO: There's likely a better way to accomplish this, but since the
// application is going down lost memory isn't the end of the world. But with a regular lock
// there's seg faults when node shuts down.
global_locker = new Locker(Isolate::GetCurrent());
current = NULL;
// Fiber constructor
tmpl = Persistent<FunctionTemplate>::New(FunctionTemplate::New(New));
tmpl->SetClassName(String::NewSymbol("Fiber"));
// Guard which only allows these methods to be called on a fiber; prevents
// `fiber.run.call({})` from seg faulting.
Handle<Signature> sig = Signature::New(tmpl);
tmpl->InstanceTemplate()->SetInternalFieldCount(1);
// Fiber.prototype
Handle<ObjectTemplate> proto = tmpl->PrototypeTemplate();
proto->Set(String::NewSymbol("reset"),
FunctionTemplate::New(Reset, Handle<Value>(), sig));
proto->Set(String::NewSymbol("run"),
FunctionTemplate::New(Run, Handle<Value>(), sig));
proto->Set(String::NewSymbol("throwInto"),
FunctionTemplate::New(ThrowInto, Handle<Value>(), sig));
proto->SetAccessor(String::NewSymbol("started"), GetStarted);
// Global yield() function
Handle<Function> yield = FunctionTemplate::New(Yield)->GetFunction();
Handle<String> sym_yield = String::NewSymbol("yield");
target->Set(sym_yield, yield);
// Fiber properties
Handle<Function> fn = tmpl->GetFunction();
fn->Set(sym_yield, yield);
fn->SetAccessor(String::NewSymbol("current"), GetCurrent);
fn->SetAccessor(String::NewSymbol("poolSize"), GetPoolSize, SetPoolSize);
fn->SetAccessor(String::NewSymbol("fibersCreated"), GetFibersCreated);
// Global Fiber
target->Set(String::NewSymbol("Fiber"), fn, ReadOnly);
fiber_object = Persistent<Function>::New(fn);
}
};
Persistent<FunctionTemplate> Fiber::tmpl;
Persistent<Function> Fiber::fiber_object;
Locker* Fiber::global_locker;
Fiber* Fiber::current = NULL;
vector<Fiber*> Fiber::orphaned_fibers;
Persistent<Value> Fiber::fatal_stack;
bool did_init = false;
extern "C" void init(Handle<Object> target) {
if (did_init || !target->Get(String::New("Fiber"))->IsUndefined()) {
// Oh god. Node will call init() twice even though the library was loaded only once. See Node
// issue #2621 (no fix).
return;
}
did_init = true;
HandleScope scope;
Handle<Object> global = Context::GetCurrent()->Global();
Coroutine::init();
Fiber::Init(global);
// Default stack size of 64kb. Perhaps make this configurable by the run time?
Coroutine::set_stack_size(64 * 1024);
}