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-rw-r--r--chapel.html.markdown69
1 files changed, 36 insertions, 33 deletions
diff --git a/chapel.html.markdown b/chapel.html.markdown
index 6fe7c1b0..bbbf50e8 100644
--- a/chapel.html.markdown
+++ b/chapel.html.markdown
@@ -765,6 +765,42 @@ proc countdown( seconds: int ){
}
}
+// Atomic variables, common to many languages, are ones whose operations
+// occur uninterupted. Multiple threads can both modify atomic variables
+// and can know that their values are safe.
+// Chapel atomic variables can be of type bool, int, uint, and real.
+var uranium: atomic int;
+uranium.write( 238 ); // atomically write a variable
+writeln( uranium.read() ); // atomically read a variable
+// operations are described as functions, you could define your own operators.
+uranium.sub( 3 ); // atomically subtract a variable
+writeln( uranium.read() );
+var replaceWith = 239;
+var was = uranium.exchange( replaceWith );
+writeln( "uranium was ", was, " but is now ", replaceWith );
+var isEqualTo = 235;
+if uranium.compareExchange( isEqualTo, replaceWith ) {
+ writeln( "uranium was equal to ", isEqualTo,
+ " so replaced value with ", replaceWith );
+} else {
+ writeln( "uranium was not equal to ", isEqualTo,
+ " value stays the same... whatever it was" );
+}
+
+sync {
+ begin {
+ writeln( "Waiting to for uranium to be ", isEqualTo );
+ uranium.waitFor( isEqualTo );
+ writeln( "Uranium was set (by someone) to ", isEqualTo );
+ }
+
+ begin {
+ writeln( "Waiting to write uranium to ", isEqualTo );
+ countdown( 3 );
+ uranium.write( isEqualTo );
+ }
+}
+
// sync vars have two states: empty and full.
// If you read an empty variable or write a full variable, you are waited
// until the variable is full or empty again
@@ -801,39 +837,6 @@ sync {
someSingleVar$ = 5; // first and only write ever.
}
}
-
-// atomic variables can be of type bool, int, uint, and real of any size.
-var uranium: atomic int;
-uranium.write( 238 ); // atomically write a variable
-writeln( uranium.read() ); // atomically read a variable
-// operations are described as functions, you could define your own operators.
-uranium.sub( 3 ); // atomically subtract a variable
-writeln( uranium.read() );
-var replaceWith = 239;
-var was = uranium.exchange( replaceWith );
-writeln( "uranium was ", was, " but is now ", replaceWith );
-var isEqualTo = 235;
-if uranium.compareExchange( isEqualTo, replaceWith ) {
- writeln( "uranium was equal to ", isEqualTo,
- " so replaced value with ", replaceWith );
-} else {
- writeln( "uranium was not equal to ", isEqualTo,
- " value stays the same... whatever it was" );
-}
-
-sync {
- begin {
- writeln( "Waiting to for uranium to be ", isEqualTo );
- uranium.waitFor( isEqualTo );
- writeln( "Uranium was set (by someone) to ", isEqualTo );
- }
-
- begin {
- writeln( "Waiting to write uranium to ", isEqualTo );
- countdown( 3 );
- uranium.write( isEqualTo );
- }
-}
```
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