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Modified the ImapToken caching logic to include qstring tokens
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Also reduced memory allocations in ImapTokenCache.AddOrGet()
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@jstedfast
jstedfast committed Aug 26, 2023
1 parent 53f379e commit 4cd4377
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Showing 3 changed files with 88 additions and 47 deletions.
10 changes: 3 additions & 7 deletions MailKit/Net/Imap/ImapStream.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -587,9 +587,7 @@ ImapToken ReadQuotedStringToken (CancellationToken cancellationToken)
while (!TryReadQuotedString (builder, ref escaped))
ReadAhead (2, cancellationToken);

var qstring = builder.ToString ();

return ImapToken.Create (ImapTokenType.QString, qstring);
return ImapToken.Create (ImapTokenType.QString, builder);
}
}

Expand All @@ -604,9 +602,7 @@ async ValueTask<ImapToken> ReadQuotedStringTokenAsync (CancellationToken cancell
while (!TryReadQuotedString (builder, ref escaped))
await ReadAheadAsync (2, cancellationToken).ConfigureAwait (false);

var qstring = builder.ToString ();

return ImapToken.Create (ImapTokenType.QString, qstring);
return ImapToken.Create (ImapTokenType.QString, builder);
}
}

Expand Down Expand Up @@ -781,7 +777,7 @@ async ValueTask<ImapToken> ReadLiteralTokenAsync (CancellationToken cancellation
inputIndex++;

if (!builder.TryParse (1, endIndex, out literalDataLeft) || literalDataLeft < 0)
return ImapToken.Create (ImapTokenType.Error, builder.ToString ());
return ImapToken.CreateError (builder);

Mode = ImapStreamMode.Literal;

Expand Down
36 changes: 24 additions & 12 deletions MailKit/Net/Imap/ImapToken.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -127,6 +127,19 @@ public static ImapToken Create (ImapTokenType type, int literalLength)
return new ImapToken (type, literalLength);
}

static bool IsAscii (ByteArrayBuilder builder)
{
for (int i = 0; i < builder.Length; i++) {
byte c = builder[i];

// Disregard any non-ASCII tokens.
if (c < 32 || c >= 127)
return false;
}

return true;
}

static bool IsCacheable (ByteArrayBuilder builder)
{
if (builder.Length < 2 || builder.Length > 32)
Expand All @@ -140,19 +153,12 @@ static bool IsCacheable (ByteArrayBuilder builder)
if (builder[0] >= (byte) 'A' && builder[0] <= (byte) 'Z' && builder[1] >= (byte) '0' && builder[1] <= (byte) '9')
return false;

for (int i = 0; i < builder.Length; i++) {
byte c = (byte) builder[i];

// Disregard any non-ASCII "atoms".
if (c <= 32 || c >= 127)
return false;
}

return true;
return IsAscii (builder);
}

public static ImapToken Create (ImapTokenType type, ByteArrayBuilder builder)
{
bool cachable = false;
string value;

if (type == ImapTokenType.Flag) {
Expand All @@ -162,6 +168,8 @@ public static ImapToken Create (ImapTokenType type, ByteArrayBuilder builder)
if (builder.Equals (value, true))
return token;
}

cachable = IsAscii (builder);
} else if (type == ImapTokenType.Atom) {
if (builder.Equals ("NIL", true)) {
// Look for the cached NIL token that matches this capitalization.
Expand Down Expand Up @@ -207,19 +215,23 @@ public static ImapToken Create (ImapTokenType type, ByteArrayBuilder builder)
return XGMMsgId;
if (builder.Equals ("X-GM-THRID", false))
return XGMThrId;

cachable = IsCacheable (builder);
} else if (type == ImapTokenType.QString) {
cachable = IsAscii (builder);
}

if (IsCacheable (builder))
if (cachable)
return Cache.AddOrGet (type, builder);

value = builder.ToString ();

return new ImapToken (type, value);
}

public static ImapToken Create (ImapTokenType type, string value)
public static ImapToken CreateError (ByteArrayBuilder builder)
{
return new ImapToken (type, value);
return new ImapToken (ImapTokenType.Error, builder.ToString ());
}

public override string ToString ()
Expand Down
89 changes: 61 additions & 28 deletions MailKit/Net/Imap/ImapTokenCache.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -36,44 +36,49 @@ class ImapTokenCache

readonly Dictionary<ImapTokenKey, LinkedListNode<ImapTokenItem>> cache;
readonly LinkedList<ImapTokenItem> list;
readonly ImapTokenKey lookupKey;

public ImapTokenCache ()
{
cache = new Dictionary<ImapTokenKey, LinkedListNode<ImapTokenItem>> ();
list = new LinkedList<ImapTokenItem> ();
lookupKey = new ImapTokenKey ();
}

public ImapToken AddOrGet (ImapTokenType type, ByteArrayBuilder builder)
{
// Note: This ImapTokenKey .ctor does not duplicate the buffer and is meant as a temporary key
// in order to avoid memory allocations for lookup purposes.
var key = new ImapTokenKey (builder.GetBuffer (), builder.Length);

lock (cache) {
if (cache.TryGetValue (key, out var node)) {
// lookupKey is a pre-allocated key used for lookups
lookupKey.Init (type, builder.GetBuffer (), builder.Length);

if (cache.TryGetValue (lookupKey, out var node)) {
// move the node to the head of the list
list.Remove (node);
list.AddFirst (node);
node.Value.Count++;

return node.Value.Token;
}

var token = new ImapToken (type, builder.ToString ());

if (cache.Count >= capacity) {
// remove the least recently used token
node = list.Last;
list.RemoveLast ();
cache.Remove (node.Value.Key);
}

var token = new ImapToken (type, builder.ToString ());

// Note: We recreate the key here so we have a permanent key. Also this allows for reuse of the token's Value string.
key = new ImapTokenKey ((string) token.Value);
// re-use the node, item and key to avoid allocations
node.Value.Key.Init (type, (string) token.Value);
node.Value.Token = token;
} else {
var key = new ImapTokenKey (type, (string) token.Value);
var item = new ImapTokenItem (key, token);

var item = new ImapTokenItem (key, token);
node = new LinkedListNode<ImapTokenItem> (item);
}

node = new LinkedListNode<ImapTokenItem> (item);
cache.Add (key, node);
cache.Add (node.Value.Key, node);
list.AddFirst (node);

return token;
Expand All @@ -82,33 +87,49 @@ public ImapToken AddOrGet (ImapTokenType type, ByteArrayBuilder builder)

class ImapTokenKey
{
readonly byte[] byteArrayKey;
readonly string stringKey;
readonly int length;
readonly int hashCode;
ImapTokenType type;
byte[] byteArrayKey;
string stringKey;
int length;
int hashCode;

public ImapTokenKey ()
{
}

public ImapTokenKey (byte[] key, int len)
public ImapTokenKey (ImapTokenType type, string key)
{
byteArrayKey = key;
length = len;
Init (type, key);
}

public void Init (ImapTokenType type, byte[] key, int length)
{
this.type = type;
this.byteArrayKey = key;
this.stringKey = null;
this.length = length;

var hash = new HashCode ();
hash.Add ((int) type);
for (int i = 0; i < length; i++)
hash.Add ((char) key[i]);

hashCode = hash.ToHashCode ();
this.hashCode = hash.ToHashCode ();
}

public ImapTokenKey (string key)
public void Init (ImapTokenType type, string key)
{
stringKey = key;
length = key.Length;
this.type = type;
this.byteArrayKey = null;
this.stringKey = key;
this.length = key.Length;

var hash = new HashCode ();
hash.Add ((int) type);
for (int i = 0; i < length; i++)
hash.Add (key[i]);

hashCode = hash.ToHashCode ();
this.hashCode = hash.ToHashCode ();
}

static bool Equals (string str, byte[] bytes)
Expand All @@ -123,7 +144,7 @@ static bool Equals (string str, byte[] bytes)

static bool Equals (ImapTokenKey self, ImapTokenKey other)
{
if (self.length != other.length)
if (self.type != other.type || self.length != other.length)
return false;

if (self.stringKey != null) {
Expand Down Expand Up @@ -153,17 +174,29 @@ public override int GetHashCode ()
{
return hashCode;
}

public override string ToString ()
{
return string.Format ("{0}: {1}", type, stringKey ?? Encoding.UTF8.GetString (byteArrayKey, 0, length));
}
}

class ImapTokenItem
{
public readonly ImapTokenKey Key;
public readonly ImapToken Token;
public ImapTokenKey Key;
public ImapToken Token;
public int Count;

public ImapTokenItem (ImapTokenKey key, ImapToken token)
{
Key = key;
Token = token;
Count = 1;
}

public override string ToString ()
{
return $"{Count}";
}
}
}
Expand Down

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