aboutsummaryrefslogtreecommitdiff
path: root/README.md
blob: 1dbbb84ac2962fbed11fa582cc0c7c9a10e9cf98 (plain)
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
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
SingleApplication
=================

![CI](https://github.com/itay-grudev/SingleApplication/workflows/CI:%20Build%20Test/badge.svg)

This is a replacement of the QtSingleApplication for `Qt5`.

Keeps the Primary Instance of your Application and kills each subsequent
instances. It can (if enabled) spawn secondary (non-related to the primary)
instances and can send data to the primary instance from secondary instances.

Usage
-----

The `SingleApplication` class inherits from whatever `Q[Core|Gui]Application`
class you specify via the `QAPPLICATION_CLASS` macro (`QCoreApplication` is the
default). Further usage is similar to the use of the `Q[Core|Gui]Application`
classes.

The library sets up a `QLocalServer` and a `QSharedMemory` block. The first
instance of your Application is your Primary Instance. It would check if the
shared memory block exists and if not it will start a `QLocalServer` and listen
for connections. Each subsequent instance of your application would check if the
shared memory block exists and if it does, it will connect to the QLocalServer
to notify the primary instance that a new instance had been started, after which
it would terminate with status code `0`. In the Primary Instance
`SingleApplication` would emit the `instanceStarted()` signal upon detecting
that a new instance had been started.

The library uses `stdlib` to terminate the program with the `exit()` function.

You can use the library as if you use any other `QCoreApplication` derived
class:

```cpp
#include <QApplication>
#include <SingleApplication.h>

int main( int argc, char* argv[] )
{
    SingleApplication app( argc, argv );

    return app.exec();
}
```

To include the library files I would recommend that you add it as a git
submodule to your project and include it's contents with a `.pri` file. Here is
how:

```bash
git submodule add git@github.com:itay-grudev/SingleApplication.git singleapplication
```

**Qmake:**

Then include the `singleapplication.pri` file in your `.pro` project file.

```qmake
include(singleapplication/singleapplication.pri)
DEFINES += QAPPLICATION_CLASS=QApplication
```

**CMake:**

Then include the subdirectory in your `CMakeLists.txt` project file.

```cmake
set(QAPPLICATION_CLASS QApplication CACHE STRING "Inheritance class for SingleApplication")
add_subdirectory(src/third-party/singleapplication)
```

Also don't forget to specify which `QCoreApplication` class your app is using if it
is not `QCoreApplication` as in examples above.

The `Instance Started` signal
------------------------

The SingleApplication class implements a `instanceStarted()` signal. You can
bind to that signal to raise your application's window when a new instance had
been started, for example.

```cpp
// window is a QWindow instance
QObject::connect(
    &app,
    &SingleApplication::instanceStarted,
    &window,
    &QWindow::raise
);
```

Using `SingleApplication::instance()` is a neat way to get the
`SingleApplication` instance for binding to it's signals anywhere in your
program.

__Note:__ On Windows the ability to bring the application windows to the
foreground is restricted. See [Windows specific implementations](Windows.md)
for a workaround and an example implementation.


Secondary Instances
-------------------

If you want to be able to launch additional Secondary Instances (not related to
your Primary Instance) you have to enable that with the third parameter of the
`SingleApplication` constructor. The default is `false` meaning no Secondary
Instances. Here is an example of how you would start a Secondary Instance send
a message with the command line arguments to the primary instance and then shut
down.

```cpp
int main(int argc, char *argv[])
{
    SingleApplication app( argc, argv, true );

    if( app.isSecondary() ) {
        app.sendMessage(  app.arguments().join(' ')).toUtf8() );
        app.exit( 0 );
    }

    return app.exec();
}
```

*__Note:__ A secondary instance won't cause the emission of the
`instanceStarted()` signal by default. See `SingleApplication::Mode` for more
details.*

You can check whether your instance is a primary or secondary with the following
methods:

```cpp
app.isPrimary();
// or
app.isSecondary();
```

*__Note:__ If your Primary Instance is terminated a newly launched instance
will replace the Primary one even if the Secondary flag has been set.*

API
---

### Members

```cpp
SingleApplication::SingleApplication( int &argc, char *argv[], bool allowSecondary = false, Options options = Mode::User, int timeout = 100 )
```

Depending on whether `allowSecondary` is set, this constructor may terminate
your app if there is already a primary instance running. Additional `Options`
can be specified to set whether the SingleApplication block should work
user-wide or system-wide. Additionally the `Mode::SecondaryNotification` may be
used to notify the primary instance whenever a secondary instance had been
started (disabled by default). `timeout` specifies the maximum time in
milliseconds to wait for blocking operations.

*__Note:__ `argc` and `argv` may be changed as Qt removes arguments that it
recognizes.*

*__Note:__ `Mode::SecondaryNotification` only works if set on both the primary
and the secondary instance.*

*__Note:__ Operating system can restrict the shared memory blocks to the same
user, in which case the User/System modes will have no effect and the block will
be user wide.*

---

```cpp
bool SingleApplication::sendMessage( QByteArray message, int timeout = 100 )
```

Sends `message` to the Primary Instance. Uses `timeout` as a the maximum timeout
in milliseconds for blocking functions

---

```cpp
bool SingleApplication::isPrimary()
```

Returns if the instance is the primary instance.

---

```cpp
bool SingleApplication::isSecondary()
```
Returns if the instance is a secondary instance.

---

```cpp
quint32 SingleApplication::instanceId()
```

Returns a unique identifier for the current instance.

---

```cpp
qint64 SingleApplication::primaryPid()
```

Returns the process ID (PID) of the primary instance.

---

```cpp
QString SingleApplication::primaryUser()
```

Returns the username the primary instance is running as.

---

```cpp
QString SingleApplication::currentUser()
```

Returns the username the current instance is running as.

### Signals

```cpp
void SingleApplication::instanceStarted()
```

Triggered whenever a new instance had been started, except for secondary
instances if the `Mode::SecondaryNotification` flag is not specified.

---

```cpp
void SingleApplication::receivedMessage( quint32 instanceId, QByteArray message )
```

Triggered whenever there is a message received from a secondary instance.

---

### Flags

```cpp
enum SingleApplication::Mode
```

*   `Mode::User` - The SingleApplication block should apply user wide. This adds
    user specific data to the key used for the shared memory and server name.
    This is the default functionality.
*   `Mode::System` – The SingleApplication block applies system-wide.
*   `Mode::SecondaryNotification` – Whether to trigger `instanceStarted()` even
    whenever secondary instances are started.
*   `Mode::ExcludeAppPath` – Excludes the application path from the server name
    (and memory block) hash.
*   `Mode::ExcludeAppVersion` – Excludes the application version from the server
    name (and memory block) hash.

*__Note:__ `Mode::SecondaryNotification` only works if set on both the primary
and the secondary instance.*

*__Note:__ Operating system can restrict the shared memory blocks to the same
user, in which case the User/System modes will have no effect and the block will
be user wide.*

---

Versioning
----------

Each major version introduces either very significant changes or is not
backwards compatible with the previous version. Minor versions only add
additional features, bug fixes or performance improvements and are backwards
compatible with the previous release. See [`CHANGELOG.md`](CHANGELOG.md) for
more details.

Implementation
--------------

The library is implemented with a QSharedMemory block which is thread safe and
guarantees a race condition will not occur. It also uses a QLocalSocket to
notify the main process that a new instance had been spawned and thus invoke the
`instanceStarted()` signal and for messaging the primary instance.

Additionally the library can recover from being forcefully killed on *nix
systems and will reset the memory block given that there are no other
instances running.

License
-------
This library and it's supporting documentation are released under
`The MIT License (MIT)` with the exception of the Qt calculator examples which
is distributed under the BSD license.