[PATCH 1/2] Add the speculative.stp tapset

[William Cohen]

The speculative.stp tapset allow one to speculative add things to
output buffers and then later commit or discard the information in the
buffers.  Four functions in the tapset:

speculation() - function to give an id for speculative buffer
speculate() - add output to a speculative buffer
discard() - remove output for a speculative buffer
commit() - output data for a speculative buffer

Signed-off-by: William Cohen <wcohen@redhat.com>
---
 doc/SystemTap_Tapset_Reference/tapsets.tmpl |   10 +++
 tapset/speculative.stp                      |   80 +++++++++++++++++++++++++++
 2 files changed, 90 insertions(+), 0 deletions(-)
 create mode 100644 tapset/speculative.stp

diff --git a/doc/SystemTap_Tapset_Reference/tapsets.tmpl b/doc/SystemTap_Tapset_Reference/tapsets.tmpl
index 685c733..dd78a4e 100644
--- a/doc/SystemTap_Tapset_Reference/tapsets.tmpl
+++ b/doc/SystemTap_Tapset_Reference/tapsets.tmpl
@@ -389,4 +389,14 @@
 !Itapset/nfsd.stp
 !Itapset/nfsderrno.stp
   </chapter>
+
+  <chapter id="speculation.stp">
+    <title>Speculation</title>
+    <para>
+      This family of functions provides the ability to speculative record
+      information and then at a later point in the SystemTap script either
+      commit the information or discard it.
+    </para>
+!Itapset/speculative.stp
+  </chapter>
 </book>
diff --git a/tapset/speculative.stp b/tapset/speculative.stp
new file mode 100644
index 0000000..4338672
--- /dev/null
+++ b/tapset/speculative.stp
@@ -0,0 +1,80 @@
+// Speculative tapset
+// Copyright (C) 2011 Red Hat Inc.
+//
+// This file is part of systemtap, and is free software.  You can
+// redistribute it and/or modify it under the terms of the GNU General
+// Public License (GPL); either version 2, or (at your option) any
+// later version.
+
+global _spec_id
+global _spec_counter
+global _spec_buff
+global _spec_discard
+
+/**
+ * sfunction speculation - Allocate a new id for speculative output
+ *
+ * The speculation() function is called when a new speculation buffer is needed.
+ * It returns an id for the speculative output.
+ * There can be multiple threads being speculated on concurrently.
+ * This id is used by other speculation fuctions to keep the threads
+ * separate.
+ */
+function speculation:long ()
+{
+	_spec_id += 1
+	return _spec_id
+}
+
+
+/**
+ * sfunction speculate - Store a string for possible output later
+ * @id: buffer id to store the information in
+ * @output: string to write out when commit occurs
+ *
+ * Add a string to the speculaive buffer for id.
+ */
+function speculate (id:long, output:string)
+{
+	_spec_counter[id] += 1
+	_spec_buff[id, _spec_counter[id]] = output
+}
+
+
+function _spec_erase (id:long) {
+	foreach([i, counter] in _spec_discard)
+		delete _spec_buff[i, counter]
+	delete _spec_discard
+}
+
+
+/**
+ * sfunction discard - Discard all output related to a speculation buffer
+ * @id: of the buffer to store the information in
+ *
+ */
+function discard (id:long)
+{
+	foreach([i, counter] in _spec_buff)
+		if (i==id) _spec_discard[i, counter] = 1
+	_spec_erase (id)
+}
+
+
+/**
+ * sfunction commit - Write out all output related to a speculation buffer
+ * @id: of the buffer to store the information in
+ *
+ * Output all the output for @id in the order that it was entered into
+ * the speculative buffer by speculative().
+ */
+function commit (id:long)
+{
+	foreach([i, counter+] in _spec_buff) {
+		if (i==id) {
+			printf("%s", _spec_buff[i, counter])
+			_spec_discard[i, counter] = 1
+		}
+	}
+	_spec_erase (id)
+}
-- 
1.7.1