It is relatively rare that the Config instance is modified from
application code. When it is, we usually are working on a small
set of values read from .git/config or ~/.gitconfig. Making the
class thread-safe through basic copy-on-write semantics for its
inner collection of entries simplifies the locking and permits us
to optimize for the much more common read path.
Signed-off-by: Shawn O. Pearce <spearce@xxxxxxxxxxx>
---
.../src/org/spearce/jgit/lib/Config.java | 85 +++++++++++++++++---
1 files changed, 72 insertions(+), 13 deletions(-)
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/Config.java b/org.spearce.jgit/src/org/spearce/jgit/lib/Config.java
index f4e78f3..4d4b315 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/Config.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/Config.java
@@ -46,6 +46,7 @@
import java.util.HashSet;
import java.util.List;
import java.util.Set;
+import java.util.concurrent.atomic.AtomicReference;
import org.spearce.jgit.errors.ConfigInvalidException;
import org.spearce.jgit.util.StringUtils;
@@ -60,9 +61,15 @@
private static final long MiB = 1024 * KiB;
private static final long GiB = 1024 * MiB;
- private List<Entry> entries;
+ /**
+ * Immutable current state of the configuration data.
+ * <p>
+ * This state is copy-on-write. It should always contain an immutable list
+ * of the configuration keys/values.
+ */
+ private final AtomicReference<State> state;
- final Config baseConfig;
+ private final Config baseConfig;
/**
* Magic value indicating a missing entry.
@@ -87,7 +94,7 @@ public Config() {
*/
public Config(Config defaultConfig) {
baseConfig = defaultConfig;
- clear();
+ state = new AtomicReference<State>(newState());
}
/**
@@ -358,7 +365,7 @@ public String getString(final String section, String subsection,
*/
public Set<String> getSubsections(final String section) {
final Set<String> result = new HashSet<String>();
- for (final Entry e : entries) {
+ for (final Entry e : state.get().entryList) {
if (StringUtils.equalsIgnoreCase(section, e.section)
&& e.subsection != null)
result.add(e.subsection);
@@ -382,7 +389,7 @@ else if (baseConfig != null)
private List<String> getRawStringList(final String section,
final String subsection, final String name) {
List<String> r = null;
- for (final Entry e : entries) {
+ for (final Entry e : state.get().entryList) {
if (e.match(section, subsection, name))
r = add(r, e.value);
}
@@ -541,6 +548,17 @@ public void unset(final String section, final String subsection,
*/
public void setStringList(final String section, final String subsection,
final String name, final List<String> values) {
+ State src, res;
+ do {
+ src = state.get();
+ res = replaceStringList(src, section, subsection, name, values);
+ } while (!state.compareAndSet(src, res));
+ }
+
+ private State replaceStringList(final State srcState,
+ final String section, final String subsection, final String name,
+ final List<String> values) {
+ final List<Entry> entries = copy(srcState, values);
int entryIndex = 0;
int valueIndex = 0;
int insertPosition = -1;
@@ -548,11 +566,12 @@ public void setStringList(final String section, final String subsection,
// Reset the first n Entry objects that match this input name.
//
while (entryIndex < entries.size() && valueIndex < values.size()) {
- final Entry e = entries.get(entryIndex++);
+ final Entry e = entries.get(entryIndex);
if (e.match(section, subsection, name)) {
- e.value = values.get(valueIndex++);
- insertPosition = entryIndex;
+ entries.set(entryIndex, e.forValue(values.get(valueIndex++)));
+ insertPosition = entryIndex + 1;
}
+ entryIndex++;
}
// Remove any extra Entry objects that we no longer need.
@@ -573,7 +592,7 @@ public void setStringList(final String section, final String subsection,
// is already a section available that matches. Insert
// after the last key of that section.
//
- insertPosition = findSectionEnd(section, subsection);
+ insertPosition = findSectionEnd(entries, section, subsection);
}
if (insertPosition < 0) {
// We didn't find any matching section header for this key,
@@ -594,9 +613,22 @@ public void setStringList(final String section, final String subsection,
entries.add(insertPosition++, e);
}
}
+
+ return newState(entries);
+ }
+
+ private static List<Entry> copy(final State src, final List<String> values) {
+ // At worst we need to insert 1 line for each value, plus 1 line
+ // for a new section header. Assume that and allocate the space.
+ //
+ final int max = src.entryList.size() + values.size() + 1;
+ final ArrayList<Entry> r = new ArrayList<Entry>(max);
+ r.addAll(src.entryList);
+ return r;
}
- private int findSectionEnd(final String section, final String subsection) {
+ private static int findSectionEnd(final List<Entry> entries,
+ final String section, final String subsection) {
for (int i = 0; i < entries.size(); i++) {
Entry e = entries.get(i);
if (e.match(section, subsection, null)) {
@@ -619,7 +651,7 @@ private int findSectionEnd(final String section, final String subsection) {
*/
public String toText() {
final StringBuilder out = new StringBuilder();
- for (final Entry e : entries) {
+ for (final Entry e : state.get().entryList) {
if (e.prefix != null)
out.append(e.prefix);
if (e.section != null && e.name == null) {
@@ -721,14 +753,22 @@ public void fromText(final String text) throws ConfigInvalidException {
throw new ConfigInvalidException("Invalid line in config file");
}
- entries = newEntries;
+ state.set(newState(newEntries));
+ }
+
+ private State newState() {
+ return new State(Collections.<Entry> emptyList());
+ }
+
+ private State newState(final List<Entry> entries) {
+ return new State(Collections.unmodifiableList(entries));
}
/**
* Clear the configuration file
*/
protected void clear() {
- entries = new ArrayList<Entry>();
+ state.set(newState());
}
private static String readSectionName(final StringReader in)
@@ -893,6 +933,14 @@ private static String readValue(final StringReader in, boolean quote,
return value.length() > 0 ? value.toString() : null;
}
+ private static class State {
+ final List<Entry> entryList;
+
+ State(List<Entry> entries) {
+ entryList = entries;
+ }
+ }
+
/**
* The configuration file entry
*/
@@ -927,6 +975,17 @@ private static String readValue(final StringReader in, boolean quote,
*/
String suffix;
+ Entry forValue(final String newValue) {
+ final Entry e = new Entry();
+ e.prefix = prefix;
+ e.section = section;
+ e.subsection = subsection;
+ e.name = name;
+ e.value = newValue;
+ e.suffix = suffix;
+ return e;
+ }
+
boolean match(final String aSection, final String aSubsection,
final String aKey) {
return eqIgnoreCase(section, aSection)
--
1.6.4.rc2.216.g769fa
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