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Mutex: Difference between revisions
→{{header|D}}: +clarification
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private:
static num = 0;
}
</lang>
Keep in mind that '''synchronized''' used as above works on a per-class-instance basis.
This is described in [[http://digitalmars.com/d/1.0/class.html##synchronized-functions|documentation]].
The following example tries to illustrate the problem:
<lang D>import tango.core.Thread, tango.io.Stdout, tango.util.log.Trace;
class Synced {
public synchronized int func (int input) {
Trace.formatln("in {} at func enter: {}", input, foo);
// stupid loop to consume some time
int arg;
for (int i = 0; i < 1000*input; ++i) {
for (int j = 0; j < 10_000; ++j) arg += j;
}
foo += input;
Trace.formatln("in {} at func exit: {}", input, foo);
return arg;
}
private static int foo;
}
void main(char[][] args) {
SimpleThread[] ht;
Stdout.print( "Starting application..." ).newline;
for (int i=0; i < 3; i++) {
Stdout.print( "Starting thread for: " )(i).newline;
ht ~= new SimpleThread(i+1);
ht[i].start();
}
// wait for all threads
foreach( s; ht )
s.join();
}
class SimpleThread : Thread
{
private int d_id;
this (int id) {
super (&run);
d_id = id;
}
void run() {
auto tested = new Synced;
Trace.formatln ("in run() {}", d_id);
tested.func(d_id);
}
}</lang>
Every created thread creates its own '''Synced''' object, and because the monitor created by synchronized statement is created for every object,
each thread can enter the ''func()'' method.
To resolve that either ''func()'' could be done static (static member functions are synchronized per-class basis) or '''synchronized block''' should be used
like here:
<lang D>
class Synced {
public int func (int input) {
synchronized(Synced.classinfo) {
// ...
foo += input;
// ...
}
return arg;
}
private static int foo;
}
</lang>
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