1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
|
/**
* @file lazyeventapi.h
* @author Nat Goodspeed
* @date 2022-06-16
* @brief Declaring a static module-scope LazyEventAPI registers a specific
* LLEventAPI for future on-demand instantiation.
*
* $LicenseInfo:firstyear=2022&license=viewerlgpl$
* Copyright (c) 2022, Linden Research, Inc.
* $/LicenseInfo$
*/
#if ! defined(LL_LAZYEVENTAPI_H)
#define LL_LAZYEVENTAPI_H
#include "apply.h"
#include "lleventapi.h"
#include "llinstancetracker.h"
#include <boost/signals2/signal.hpp>
#include <string>
#include <tuple>
#include <utility> // std::pair
#include <vector>
namespace LL
{
/**
* Bundle params we want to pass to LLEventAPI's protected constructor. We
* package them this way so a subclass constructor can simply forward an
* opaque reference to the LLEventAPI constructor.
*/
// This is a class instead of a plain struct mostly so when we forward-
// declare it we don't have to remember the distinction.
class LazyEventAPIParams
{
public:
// package the parameters used by the normal LLEventAPI constructor
std::string name, desc, field;
// bundle LLEventAPI::add() calls collected by LazyEventAPI::add(), so
// the special LLEventAPI constructor we engage can "play back" those
// add() calls
boost::signals2::signal<void(LLEventAPI*)> init;
};
/**
* LazyEventAPIBase implements most of the functionality of LazyEventAPI
* (q.v.), but we need the LazyEventAPI template subclass so we can accept
* the specific LLEventAPI subclass type.
*/
// No LLInstanceTracker key: we don't need to find a specific instance,
// LLLeapListener just needs to be able to enumerate all instances.
class LazyEventAPIBase: public LLInstanceTracker<LazyEventAPIBase>
{
public:
LazyEventAPIBase(const std::string& name, const std::string& desc,
const std::string& field);
virtual ~LazyEventAPIBase();
// Do not copy or move: once constructed, LazyEventAPIBase must stay
// put: we bind its instance pointer into a callback.
LazyEventAPIBase(const LazyEventAPIBase&) = delete;
LazyEventAPIBase(LazyEventAPIBase&&) = delete;
LazyEventAPIBase& operator=(const LazyEventAPIBase&) = delete;
LazyEventAPIBase& operator=(LazyEventAPIBase&&) = delete;
// capture add() calls we want to play back on LLEventAPI construction
template <typename... ARGS>
void add(const std::string& name, const std::string& desc, ARGS&&... rest)
{
// capture the metadata separately
mOperations.push_back(std::make_pair(name, desc));
// Use connect_extended() so the lambda is passed its own
// connection.
// apply() can't accept a template per se; it needs a particular
// specialization. Specialize out here to work around a clang bug:
// https://github.com/llvm/llvm-project/issues/41999
auto func{ &LazyEventAPIBase::add_trampoline
<const std::string&, const std::string&, ARGS...> };
// We can't bind an unexpanded parameter pack into a lambda --
// shame really. Instead, capture all our args as a std::tuple and
// then, in the lambda, use apply() to pass to add_trampoline().
mParams.init.connect_extended(
[func, args = std::make_tuple(name, desc, std::forward<ARGS>(rest)...)]
(const boost::signals2::connection& conn, LLEventAPI* instance)
{
// we only need this connection once
conn.disconnect();
// apply() expects a tuple specifying ALL the arguments,
// so prepend instance.
apply(func, std::tuple_cat(std::make_tuple(instance), args));
});
}
// The following queries mimic the LLEventAPI / LLEventDispatcher
// query API.
// Get the string name of the subject LLEventAPI
std::string getName() const { return mParams.name; }
// Get the documentation string
std::string getDesc() const { return mParams.desc; }
// Retrieve the LLSD key we use for dispatching
std::string getDispatchKey() const { return mParams.field; }
// operations
using NameDesc = std::pair<std::string, std::string>;
private:
// metadata that might be queried by LLLeapListener
std::vector<NameDesc> mOperations;
public:
using const_iterator = decltype(mOperations)::const_iterator;
const_iterator begin() const { return mOperations.begin(); }
const_iterator end() const { return mOperations.end(); }
LLSD getMetadata(const std::string& name) const;
protected:
// Params with which to instantiate the companion LLEventAPI subclass
LazyEventAPIParams mParams;
private:
// true if we successfully registered our LLEventAPI on construction
bool mRegistered;
// actually instantiate the companion LLEventAPI subclass
virtual LLEventPump* construct(const std::string& name) = 0;
// Passing an overloaded function to any function that accepts an
// arbitrary callable is a PITB because you have to specify the
// correct overload. What we want is for the compiler to select the
// correct overload, based on the carefully-wrought enable_ifs in
// LLEventDispatcher. This (one and only) add_trampoline() method
// exists solely to pass to LL::apply(). Once add_trampoline() is
// called with the expanded arguments, we hope the compiler will Do
// The Right Thing in selecting the correct LLEventAPI::add()
// overload.
template <typename... ARGS>
static
void add_trampoline(LLEventAPI* instance, ARGS&&... args)
{
instance->add(std::forward<ARGS>(args)...);
}
};
/**
* LazyEventAPI provides a way to register a particular LLEventAPI to be
* instantiated on demand, that is, when its name is passed to
* LLEventPumps::obtain().
*
* Derive your listener from LLEventAPI as usual, with its various
* operation methods, but code your constructor to accept
* <tt>(const LL::LazyEventAPIParams& params)</tt>
* and forward that reference to (the protected)
* <tt>LLEventAPI(const LL::LazyEventAPIParams&)</tt> constructor.
*
* Then derive your listener registrar from
* <tt>LazyEventAPI<your LLEventAPI subclass></tt>. The constructor should
* look very like a traditional LLEventAPI constructor:
*
* * pass (name, desc [, field]) to LazyEventAPI's constructor
* * in the body, make a series of add() calls referencing your LLEventAPI
* subclass methods.
*
* You may use any LLEventAPI::add() methods, that is, any
* LLEventDispatcher::add() methods. But the target methods you pass to
* add() must belong to your LLEventAPI subclass, not the LazyEventAPI
* subclass.
*
* Declare a static instance of your LazyEventAPI listener registrar
* class. When it's constructed at static initialization time, it will
* register your LLEventAPI subclass with LLEventPumps. It will also
* collect metadata for the LLEventAPI and its operations to provide to
* LLLeapListener's introspection queries.
*
* When someone later calls LLEventPumps::obtain() to post an event to
* your LLEventAPI subclass, obtain() will instantiate it using
* LazyEventAPI's name, desc, field and add() calls.
*/
template <class EVENTAPI>
class LazyEventAPI: public LazyEventAPIBase
{
public:
// for subclass constructor to reference handler methods
using listener = EVENTAPI;
LazyEventAPI(const std::string& name, const std::string& desc,
const std::string& field="op"):
// Forward ctor params to LazyEventAPIBase
LazyEventAPIBase(name, desc, field)
{}
private:
LLEventPump* construct(const std::string& /*name*/) override
{
// base class has carefully assembled LazyEventAPIParams embedded
// in this instance, just pass to LLEventAPI subclass constructor
return new EVENTAPI(mParams);
}
};
} // namespace LL
#endif /* ! defined(LL_LAZYEVENTAPI_H) */
|
