Changes between Version 36 and Version 37 of Language

Timestamp:

05/21/23 10:12:22 (3 years ago)

Author:

siegel

Comment:

--

Language

@@ -278 +278 @@
 
 A spawn expression is an expression with side-effects.
-It spawns a new process and returns a reference to the new process, i.e., an object of type $proc.
-The syntax is the same as a procedure invocation with the keyword `$spawn` inserted in front:
-{{{
-$spawn f(expr1, ..., exprn)
-}}}
+It spawns a new process and returns a reference to the new process, i.e., an object of [#proc-type type $proc].
+The syntax is the same as a function call with the keyword `$spawn` inserted in front:
+  `$spawn` ''function-expr'' `(` ( ''expr'' ( `,` expr )* )? `)`
+Example:
+{{{
+$spawn f(3.14, x+2*y)
+}}}
+
 Typically the returned value is assigned to a variable, e.g.,
 {{{
 $proc p = $spawn f(i);
 }}}
-If the function `f` returns a value, that value is simply ignored.
+If the function `f` returns a value, that value is ignored.
 
 == Statements #statements
@@ -293 +296 @@
 === Atomic blocks: `$atomic` #atomic
 
-An ''atomic block'' is a statement of the form
+An ''atomic block'' has syntax
+  `$atomic` `{` ( ''stmt'' ( `,` stmt )* )? `}`
+For example,
 {{{
 $atomic {
-  stmt1;
-  stmt2;
-  ...
-}
-}}}
-and indicates that the statements comprising the block should be executed without the intervention of other processes.
+  x=x+1;
+  y=2*x+y;
+}
+}}}
+It indicates that the statements comprising the block should be executed without the intervention of other processes.
 
 More precisely, there is a global atomic lock which is initially free.
@@ -323 +327 @@
 
 Atomic blocks may be nested.
-Hence the atomic lock is held with a certain multiplicity.
-Each time the process enters an atomic block, the multiplicity is incremented.
-Each time it leaves an atomic block, the multiplicity is decremented.
-When the multiplicity hits 0, the atomic lock is released.
+The semantics are as follows.
+Each process maintains a counter which records the multiplicity with which it owns the atomic lock.
+These counters are initially 0.
+When a process acquires the lock, the counter is set to 1.
+Each time the process attempts to enter an atomic block when it already owns the lock, it succeeds immediately and the counter is incremented.
+Each time the process leaves an atomic block, the counter is decremented.
+When the counter reaches 0, the lock is released.
+
 Execution of a `$yield` does not change the multiplicity; the process releases the lock but maintains the multiplicity,
 so that when the lock is re-obtained, the original multiplicity is still in place.