Changeset 62b5940

Timestamp:

Mar 20, 2025, 1:06:08 AM (36 hours ago)

Author:

Michael Brooks <mlbrooks@…>

Branches:

master

Children:

f5bf3c2

Parents:

5329cba

Message:

Flesh out the string_sharectx demo

Location:

doc/theses/mike_brooks_MMath

Files:

• pictures/string-sharectx.pdf (added)
• pictures/string-sharectx.vsdx (added)
• programs/sharectx.run.cfa (modified) (2 diffs)
• string.tex (modified) (1 diff)

doc/theses/mike_brooks_MMath/programs/sharectx.run.cfa ¶

@@ -1 +1 @@
 #include <string.hfa>
 #include <string_sharectx.hfa>
-
-void a() {}
-void b() {}
-void c() {}
-void d() {}
-void e() {}
 
 
@@ -14 +8 @@
 
 
-
-
-
-
-void helper2() {
-        c();
-        string_sharectx c = {NEW_SHARING};
-        d();
+void a( string & sm ) {
+        string sm_a = sm; // share
 }
-void helper1() {
-        a();
-        string_sharectx c = {NO_SHARING};
-        b();
-        helper2();
-        e();
+void b( string & sm ) {
+        string sm_b = sm; // share
+}
+void c( string & sm, string & sh1 ) {
+        string sm_c = sm; // copy
+        string sh1_c = sh1; // copy
+}
+void d( string & sm, string & sh1 ) {
+        string sm_d = sm; // copy
+        string sh1_d = sh1; // copy
+}
+void e( string & sm, string & sh1, string & sh2 ) {
+        string sm_e = sm; // copy
+        string sh1_e = sh1; // copy
+        string sh2_e = sh2; // share
+}
+void f( string & sm, string & sh1 ) {
+        string sm_f = sm; // copy
+        string sh1_f = sh1; // copy
+}
+void g( string & sm ) {
+        string sm_g = sm; // share
+}
+void helper2( string & sm, string & sh1 ) {
+        d( sm, sh1 );
+        string_sharectx ctx_on = {NEW_SHARING};
+        string sh2 = "sh2";
+        e( sm, sh1, sh2 );
+}
+void helper1( string & sm ) {
+        b( sm );
+        string_sharectx ctx_off = {NO_SHARING};
+        string sh1 = "sh1";
+        c( sm, sh1 );
+        helper2( sm, sh1 );
+        f( sm, sh1 );
 }
 int main() {
-        helper1();
+        string sm = "sm";
+        a( sm );
+        helper1( sm );
+        g( sm );
 }
-

doc/theses/mike_brooks_MMath/string.tex ¶

@@ -470 +470 @@
 Hence, concurrent users of string objects must still bring their own mutual exclusion, but the string library does not add any cross thread uses that are not apparent in a user's code.
 
-\PAB{I could not get this to do anything.}
-The \CFA string library does provides a @string_sharectx@ type to control an ambient sharing context for the current thread.
+The \CFA string library provides the type @string_sharectx@to control an ambient sharing context for the current thread.
 It allows two adjustments: to opt out of sharing entirely or to begin sharing within a private context.
 Either way, the chosen mode applies only to the current thread, for the duration of the lifetime of the created  @string_sharectx@ object, up to being suspended by child lifetimes of different contexts.
+\VRef[Figure]{fig:string-sharectx} illustrates its behaviour.
+Executing the example does not produce an interesting outcome.
+But the comments indicate when the logical copy operation runs with
+\begin{description}
+    \item[share:] the copy being deferred, as described through the rest of this section (fast), or
+    \item[copy:] the copy performed eagerly (slow).
+\end{description}
+Only eager copies can cross @string_sharectx@ boundaries.
 The intended use is with stack-managed lifetimes, in which the established context lasts until the current function returns, and affects all functions called that do not create their own contexts.
-\lstinputlisting[language=CFA, firstline=20, lastline=34]{sharectx.run.cfa}
 In this example, the single-letter functions are called in alphabetic order.
-The functions @a@ and @d@ share string character ranges within themselves, but not with each other.
-The functions @b@, @c@ and @e@ never share anything.
+The functions @a@, @b@ and @g@ share string character ranges with each other, because they occupy a common sharing-enabled context.
+The function @e@ shares within itself (because its is in a sharing-enabled context), but not with the rest of the program (because its context is not occupied by any of the rest of the program).
+The functions @c@, @d@ and @f@ never share anything, because they are in a sharing-disabled context.
+
+
+\begin{figure}
+    \begin{tabular}{ll}
+        \lstinputlisting[language=CFA, firstline=10, lastline=55]{sharectx.run.cfa}
+        &
+        \includegraphics{string-sharectx.pdf}
+    \end{tabular}
+        \caption{Controlling copying vs sharing of strings using \lstinline{string_sharectx}.}
+        \label{fig:string-sharectx}
+\end{figure}
+
 
 [ TODO: true up with ``is thread local'' (implement that and expand this discussion to give a concurrent example, or adjust this wording) ]