There is a project as your work. http://code.google.com/p/js-coroutine/
On Mar 2, 8:18 pm, ejpbruel <[email protected]> wrote: > Hello, > > I am currently working on a proof of concept of using the stdlibc > makecontext/swapcontext functions in conjunction with v8. I know that > v8 is technically notthreadsafe, but since these functions allow the > explicit creation and scheduling ofthreadcontexts, no race > conditions should occur, so it is at least conceivable that this > willwork. > > The control flow for the sample code below is as follows: > - main() creates athreadcontext which will call a central dispatch > loop (loop()) > - main() initializes v8 with three function callbacks on the global > object (readAsync, read, and log) > - main() compiles and runs the script in str (defined at the beginning > of the script) > > - the evaluated script calls readAsync() > - readAsync() calls push() with readAysnc_helper() as argument > - push() creates a newthreadcontext which will call > readAsync_helper() > - push() and readAsync() both return > > - the evaluated script calls read() > - read() calls read_helper() directly > - read_helper() needs to do a blocking call on fd 0 (stdin), so it > calls yield() with that fd as argument > - yield() registers the current context as being blocked > - yield() switches to the context for the central dispatch loop > > - loop() first handles any newly create contexts > - the context for readAsync_helper() is newly created, so loop() > switches to there > - readAsync() also calls read_helper() > - read_helper() needs to do a (potentially) blocking call on fd 3, so > it calls yield() with that fd as argument > - yield() registers the current context as being blocked > - yield() switches to the context for the central dispatch loop > > - no more newly created contexts are available, so loop() now handles > all blocking contexts > - loop() performs a select to see which fd's become available for > reading > - fd 3 becomes available first, so loop() switches to > readAsync_helper() > - readAsync_helper() does a blocking read (which will not block > because of the select) > - readAsync_helper() calls a function object which was stored earlier > (see readAsync()) > > At this point, the callback does not seem to be called (if it were, > this should have resulted in a call to log()). Instead, V8 complains > to me: > Uncaught RangeError: Maximum call stack size exceeded > > The cause of this error is unclear to me, but I'm suspecting that it > is related to the fact that eachthreadcontext has a completely > separate stack (which I explicitly allocate using malloc()), and this > somehow confuses V8. What I need to know is why V8 gets confused over > this, and more importantly, what I need to do in order to be able to > do a callback to Javascript/call on a function object from a > differentthreadcontext than the one on which I initialized v8. > > As a sidenote, if I do *not* call the function object, the program > proceeds as expected. readAsync_helper() returns to the dispatch loop, > which will subsequently unblock and switch to read_helper() when the > user types something in the terminal (so that fd 0 becomes ready for > reading). > > Last but not least, here's the example code I used (note that a file > named test must be available in the same directory in order for it to > run correctly!): > > #include <ucontext.h> > #include <stdlib.h> > #include <fcntl.h> > #include <unistd.h> > #include <stdio.h> > #include <sys/select.h> > #include <v8-debug.h> > > using namespace v8; > > #define SIZE 1024 > > const char str[] = "readAsync(function () { log('async ok') });" > "read(); log('sync ok');"; > > ucontext_t uc; // Dispatch loop context > int nacs; > ucontext_t acs[10]; // Newly created contexts > int nfds; > fd_set fds; > ucontext_t ucs[10]; // Currently blocked context > Persistent<Context> context; > Persistent<Function> function; > > Handle<Value> log(const Arguments& args) > { > String::Utf8Value value(args[0]); > > printf("%s\n", *value); > > } > > void yield(int fd) > { > if (nfds < fd + 1) > nfds = fd + 1; > FD_SET(fd, &fds); > swapcontext(&ucs[fd], &uc); > FD_CLR(fd, &fds); > do > --fd; > while (fd >= 0 && !FD_ISSET(fd, &fds)); > if (nfds > fd + 1) > nfds = fd + 1; > > } > > void read_helper(int fd) > { > char data[SIZE]; > size_t size; > > yield(fd); > size = ::read(fd, data, SIZE); > fwrite(data, size, 1, stdout); > > } > > Handle<Value> read(const Arguments& args) > { > read_helper(0); > return Undefined(); > > } > > void readAsync_helper() > { > int fd = open("test", O_RDONLY); > > read_helper(fd); > function->Call(function, 0, 0); > > } > > void push(void (*func)(void)) > { > ucontext_t *ucp = &acs[nacs++]; > > getcontext(ucp); > ucp->uc_link = &uc; > ucp->uc_stack.ss_sp = malloc(SIGSTKSZ); > ucp->uc_stack.ss_size = SIGSTKSZ; > makecontext(ucp, func, 0); > > } > > Handle<Value> readAsync(const Arguments& args) > { > function = > Persistent<Function>::New(Handle<Function>::Cast(args[0])); > > push(readAsync_helper); > return Undefined(); > > } > > void loop() > { > fd_set readfds; > int n, i; > > for (;;) { > while (nacs > 0) > swapcontext(&uc, &acs[--nacs]); > readfds = fds; > n = select(nfds, &readfds, 0, 0, 0); > i = 0; > while (n--) { > while (!FD_ISSET(i, &readfds)) > ++i; > swapcontext(&uc, &ucs[i]); > } > } > > } > > int main(int argc, char** argv) > { > HandleScope scope; > Handle<ObjectTemplate> global; > > getcontext(&uc); > uc.uc_link = NULL; > uc.uc_stack.ss_sp = malloc(SIGSTKSZ); > uc.uc_stack.ss_size = SIGSTKSZ; > makecontext(&uc, (void (*)(void)) loop, 0); > global = ObjectTemplate::New(); > global->Set(String::New("readAsync"), > FunctionTemplate::New(readAsync)); > global->Set(String::New("read"), FunctionTemplate::New(read)); > global->Set(String::New("log"), FunctionTemplate::New(log)); > context = Context::New(0, global); > { > Context::Scope scope(context); > Handle<String> source = String::New(str); > Handle<Script> script = Script::Compile(source); > > script->Run(); > } > context.Dispose(); > return 0; > > > > } -- v8-users mailing list [email protected] http://groups.google.com/group/v8-users
