/**
 * @file   llcoros.h
 * @author Nat Goodspeed
 * @date   2009-06-02
 * @brief  Manage running boost::coroutine instances
 *
 * $LicenseInfo:firstyear=2009&license=viewerlgpl$
 * Second Life Viewer Source Code
 * Copyright (C) 2010, Linden Research, Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation;
 * version 2.1 of the License only.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
 * $/LicenseInfo$
 */

#if ! defined(LL_LLCOROS_H)
#define LL_LLCOROS_H

#include "llexception.h"
#include <boost/fiber/fss.hpp>
#include <boost/fiber/future/future.hpp>
#include <boost/fiber/future/promise.hpp>
#include <boost/fiber/recursive_mutex.hpp>
#include "mutex.h"
#include "llsingleton.h"
#include "llinstancetracker.h"
#include <boost/function.hpp>
#include <string>
#include <exception>
#include <queue>

// e.g. #include LLCOROS_MUTEX_HEADER
#define LLCOROS_MUTEX_HEADER   <boost/fiber/mutex.hpp>
#define LLCOROS_CONDVAR_HEADER <boost/fiber/condition_variable.hpp>

namespace boost {
    namespace fibers {
        class mutex;
        enum class cv_status;
        class condition_variable;
    }
}

/**
 * Registry of named Boost.Coroutine instances
 *
 * The Boost.Coroutine library supports the general case of a coroutine
 * accepting arbitrary parameters and yielding multiple (sets of) results. For
 * such use cases, it's natural for the invoking code to retain the coroutine
 * instance: the consumer repeatedly calls into the coroutine, perhaps passing
 * new parameter values, prompting it to yield its next result.
 *
 * Our typical coroutine usage is different, though. For us, coroutines
 * provide an alternative to the @c Responder pattern. Our typical coroutine
 * has @c void return, invoked in fire-and-forget mode: the handler for some
 * user gesture launches the coroutine and promptly returns to the main loop.
 * The coroutine initiates some action that will take multiple frames (e.g. a
 * capability request), waits for its result, processes it and silently steals
 * away.
 *
 * This usage poses two (related) problems:
 *
 * # Who should own the coroutine instance? If it's simply local to the
 *   handler code that launches it, return from the handler will destroy the
 *   coroutine object, terminating the coroutine.
 * # Once the coroutine terminates, in whatever way, who's responsible for
 *   cleaning up the coroutine object?
 *
 * LLCoros is a Singleton collection of currently-active coroutine instances.
 * Each has a name. You ask LLCoros to launch a new coroutine with a suggested
 * name prefix; from your prefix it generates a distinct name, registers the
 * new coroutine and returns the actual name.
 *
 * The name
 * can provide diagnostic info: we can look up the name of the
 * currently-running coroutine.
 */
class LL_COMMON_API LLCoros: public LLSingleton<LLCoros>
{
    LLSINGLETON(LLCoros);
    ~LLCoros();

    void cleanupSingleton() override;
public:
    // For debugging, return true if on the main coroutine for the current thread
    // Code that should not be executed from a coroutine should be protected by
    // llassert(LLCoros::on_main_coro())
    static bool on_main_coro();

    // For debugging, return true if on the main thread and not in a coroutine
    // Non-thread-safe code in the main loop should be protected by
    // llassert(LLCoros::on_main_thread_main_coro())
    static bool on_main_thread_main_coro();

    /// The viewer's use of the term "coroutine" became deeply embedded before
    /// the industry term "fiber" emerged to distinguish userland threads from
    /// simpler, more transient kinds of coroutines. Semantically they've
    /// always been fibers. But at this point in history, we're pretty much
    /// stuck with the term "coroutine."
    typedef boost::fibers::fiber coro;
    /// Canonical callable type
    typedef boost::function<void()> callable_t;

    /**
     * Create and start running a new coroutine with specified name. The name
     * string you pass is a suggestion; it will be tweaked for uniqueness. The
     * actual name is returned to you.
     *
     * Usage looks like this, for (e.g.) two coroutine parameters:
     * @code
     * class MyClass
     * {
     * public:
     *     ...
     *     // Do NOT NOT NOT accept reference params!
     *     // Pass by value only!
     *     void myCoroutineMethod(std::string, LLSD);
     *     ...
     * };
     * ...
     * std::string name = LLCoros::instance().launch(
     *    "mycoro", boost::bind(&MyClass::myCoroutineMethod, this,
     *                          "somestring", LLSD(17));
     * @endcode
     *
     * Your function/method can accept any parameters you want -- but ONLY BY
     * VALUE! Reference parameters are a BAD IDEA! You Have Been Warned. See
     * DEV-32777 comments for an explanation.
     *
     * Pass a nullary callable. It works to directly pass a nullary free
     * function (or static method); for other cases use a lambda expression,
     * std::bind() or boost::bind(). Of course, for a non-static class method,
     * the first parameter must be the class instance. Any other parameters
     * should be passed via the enclosing expression.
     *
     * launch() tweaks the suggested name so it won't collide with any
     * existing coroutine instance, creates the coroutine instance, registers
     * it with the tweaked name and runs it until its first wait. At that
     * point it returns the tweaked name.
     */
    std::string launch(const std::string& prefix, const callable_t& callable);

    /**
     * Abort a running coroutine by name. Normally, when a coroutine either
     * runs to completion or terminates with an exception, LLCoros quietly
     * cleans it up. This is for use only when you must explicitly interrupt
     * one prematurely. Returns @c true if the specified name was found and
     * still running at the time.
     */
//  bool kill(const std::string& name);

    /**
     * From within a coroutine, look up the (tweaked) name string by which
     * this coroutine is registered. Returns the empty string if not found
     * (e.g. if the coroutine was launched by hand rather than using
     * LLCoros::launch()).
     */
    static std::string getName();

    /**
     * rethrow() is called by the thread's main fiber to propagate an
     * exception from any coroutine into the main fiber, where it can engage
     * the normal unhandled-exception machinery, up to and including crash
     * reporting.
     *
     * LLCoros maintains a queue of otherwise-uncaught exceptions from
     * terminated coroutines. Each call to rethrow() pops the first of those
     * and rethrows it. When the queue is empty (normal case), rethrow() is a
     * no-op.
     */
    void rethrow();

    /**
     * This variation returns a name suitable for log messages: the explicit
     * name for an explicitly-launched coroutine, or "mainN" for the default
     * coroutine on a thread.
     */
    static std::string logname();

    /**
     * For delayed initialization. To be clear, this will only affect
     * coroutines launched @em after this point. The underlying facility
     * provides no way to alter the stack size of any running coroutine.
     */
    void setStackSize(S32 stacksize);

    /// diagnostic
    void printActiveCoroutines(const std::string& when=std::string());

    /// get the current coro::id for those who really really care
    static coro::id get_self();

    /**
     * Most coroutines, most of the time, don't "consume" the events for which
     * they're suspending. This way, an arbitrary number of listeners (whether
     * coroutines or simple callbacks) can be registered on a particular
     * LLEventPump, every listener responding to each of the events on that
     * LLEventPump. But a particular coroutine can assert that it will consume
     * each event for which it suspends. (See also llcoro::postAndSuspend(),
     * llcoro::VoidListener)
     */
    static void set_consuming(bool consuming);
    static bool get_consuming();

    /**
     * RAII control of the consuming flag
     */
    class OverrideConsuming
    {
    public:
        OverrideConsuming(bool consuming):
            mPrevConsuming(get_consuming())
        {
            set_consuming(consuming);
        }
        OverrideConsuming(const OverrideConsuming&) = delete;
        ~OverrideConsuming()
        {
            set_consuming(mPrevConsuming);
        }

    private:
        bool mPrevConsuming;
    };

    /// set string coroutine status for diagnostic purposes
    static void setStatus(const std::string& status);
    static std::string getStatus();

    /// RAII control of status
    class TempStatus
    {
    public:
        TempStatus(const std::string& status):
            mOldStatus(getStatus())
        {
            setStatus(status);
        }
        TempStatus(const TempStatus&) = delete;
        ~TempStatus()
        {
            setStatus(mOldStatus);
        }

    private:
        std::string mOldStatus;
    };

    /// thrown by checkStop()
    // It may sound ironic that Stop is derived from LLContinueError, but the
    // point is that LLContinueError is the category of exception that should
    // not immediately crash the viewer. Stop and its subclasses are to notify
    // coroutines that the viewer intends to shut down. The expected response
    // is to terminate the coroutine, rather than abort the viewer.
    struct Stop: public LLContinueError
    {
        Stop(const std::string& what): LLContinueError(what) {}
    };

    /// early stages
    struct Stopping: public Stop
    {
        Stopping(const std::string& what): Stop(what) {}
    };

    /// cleaning up
    struct Stopped: public Stop
    {
        Stopped(const std::string& what): Stop(what) {}
    };

    /// cleaned up -- not much survives!
    struct Shutdown: public Stop
    {
        Shutdown(const std::string& what): Stop(what) {}
    };

    /// Call this intermittently if there's a chance your coroutine might
    /// continue running into application shutdown. Throws Stop if LLCoros has
    /// been cleaned up.
    static void checkStop();

    /**
     * Aliases for promise and future. An older underlying future implementation
     * required us to wrap future; that's no longer needed. However -- if it's
     * important to restore kill() functionality, we might need to provide a
     * proxy, so continue using the aliases.
     */
    template <typename T>
    using Promise = boost::fibers::promise<T>;
    template <typename T>
    using Future = boost::fibers::future<T>;
    template <typename T>
    static Future<T> getFuture(Promise<T>& promise) { return promise.get_future(); }

    // use mutex, lock, condition_variable suitable for coroutines
    using Mutex = boost::fibers::mutex;
    using RMutex = boost::fibers::recursive_mutex;
    // With C++17, LockType is deprecated: at this point we can directly
    // declare 'std::unique_lock lk(some_mutex)' without explicitly stating
    // the mutex type. Sadly, making LockType an alias template for
    // std::unique_lock doesn't work the same way: Class Template Argument
    // Deduction only works for class templates, not alias templates.
    using LockType = std::unique_lock<Mutex>;
    using cv_status = boost::fibers::cv_status;
    using ConditionVariable = boost::fibers::condition_variable;

    /// for data local to each running coroutine
    template <typename T>
    using local_ptr = boost::fibers::fiber_specific_ptr<T>;

private:
    std::string generateDistinctName(const std::string& prefix) const;
    void toplevel(std::string name, callable_t callable);
    struct CoroData;
    static CoroData& get_CoroData(const std::string& caller);
    void saveException(const std::string& name, std::exception_ptr exc);

    struct ExceptionData
    {
        ExceptionData(const std::string& nm, std::exception_ptr exc):
            name(nm),
            exception(exc)
        {}
        // name of coroutine that originally threw this exception
        std::string name;
        // the thrown exception
        std::exception_ptr exception;
    };
    std::queue<ExceptionData> mExceptionQueue;

    S32 mStackSize;

    // coroutine-local storage, as it were: one per coro we track
    struct CoroData: public LLInstanceTracker<CoroData, std::string>
    {
        CoroData(const std::string& name);
        CoroData(int n);

        // tweaked name of the current coroutine
        const std::string mName;
        // set_consuming() state
        bool mConsuming;
        // setStatus() state
        std::string mStatus;
        F64 mCreationTime; // since epoch
    };

    // Identify the current coroutine's CoroData. This local_ptr isn't static
    // because it's a member of an LLSingleton, and we rely on it being
    // cleaned up in proper dependency order.
    local_ptr<CoroData> mCurrent;
};

namespace llcoro
{

inline
std::string logname() { return LLCoros::logname(); }

} // llcoro

#endif /* ! defined(LL_LLCOROS_H) */