Improving and adding an in-memory MRU cache to DiskBasedCertCache.

net/http/disk_based_cert_cache.cc

Index: net/http/disk_based_cert_cache.cc
diff --git a/net/http/disk_based_cert_cache.cc b/net/http/disk_based_cert_cache.cc
index b6c5b7e2731b5ede6215fefe0f2ffceba679f5e6..138d5a63195da00b6685e6ee479a27d3d67389d4 100644
--- a/net/http/disk_based_cert_cache.cc
+++ b/net/http/disk_based_cert_cache.cc
@@ -19,6 +19,9 @@ namespace net {
 
 namespace {
 
+// TODO(brandonsalmon): change this number to improve performance.
+const int kMemoryCacheMaxSize = 30;

[Ryan Sleevi, 2014/07/02 21:49:58]

size_t

+
 // Used to obtain a unique cache key for a certificate in the form of
 // "cert:<hash>".
 std::string GetCacheKeyToCert(const X509Certificate::OSCertHandle cert_handle) {
@@ -206,10 +209,9 @@ int DiskBasedCertCache::WriteWorker::DoOpen() {
 }
 
 int DiskBasedCertCache::WriteWorker::DoOpenComplete(int rv) {
-  if (rv < 0) {
-    state_ = STATE_NONE;
+  if (rv < 0)
     return rv;
-  }
+
   state_ = STATE_WRITE;
   return OK;
 }
@@ -218,10 +220,8 @@ int DiskBasedCertCache::WriteWorker::DoWrite() {
   std::string write_data;
   bool encoded = X509Certificate::GetDEREncoded(cert_handle_, &write_data);
 
-  if (!encoded) {
-    state_ = STATE_NONE;
+  if (!encoded)
     return ERR_FAILED;
-  }
 
   buffer_ = new IOBuffer(write_data.size());
   io_buf_len_ = write_data.size();
@@ -238,7 +238,6 @@ int DiskBasedCertCache::WriteWorker::DoWrite() {
 }
 
 int DiskBasedCertCache::WriteWorker::DoWriteComplete(int rv) {
-  state_ = STATE_NONE;
   if (rv < io_buf_len_)
     return ERR_FAILED;
 
@@ -287,7 +286,7 @@ class DiskBasedCertCache::ReadWorker {
   // regardless of success or failure.
   ReadWorker(disk_cache::Backend* backend,
              const std::string& key,
-             const base::Closure& cleanup_callback);
+             const GetCallback& cleanup_callback);
 
   ~ReadWorker();
 
@@ -335,15 +334,14 @@ class DiskBasedCertCache::ReadWorker {
   scoped_refptr<IOBuffer> buffer_;
   int io_buf_len_;
 
-  base::Closure cleanup_callback_;
+  GetCallback cleanup_callback_;
   std::vector<GetCallback> user_callbacks_;
   CompletionCallback io_callback_;
 };
 
-DiskBasedCertCache::ReadWorker::ReadWorker(
-    disk_cache::Backend* backend,
-    const std::string& key,
-    const base::Closure& cleanup_callback)
+DiskBasedCertCache::ReadWorker::ReadWorker(disk_cache::Backend* backend,
+                                           const std::string& key,
+                                           const GetCallback& cleanup_callback)
     : backend_(backend),
       cert_handle_(NULL),
       key_(key),
@@ -418,10 +416,9 @@ int DiskBasedCertCache::ReadWorker::DoOpen() {
 }
 
 int DiskBasedCertCache::ReadWorker::DoOpenComplete(int rv) {
-  if (rv < 0) {
-    state_ = STATE_NONE;
+  if (rv < 0)
     return rv;
-  }
+
   state_ = STATE_READ;
   return OK;
 }
@@ -435,7 +432,6 @@ int DiskBasedCertCache::ReadWorker::DoRead() {
 }
 
 int DiskBasedCertCache::ReadWorker::DoReadComplete(int rv) {
-  state_ = STATE_NONE;
   if (rv < io_buf_len_)
     return ERR_FAILED;
 
@@ -457,7 +453,7 @@ void DiskBasedCertCache::ReadWorker::RunCallbacks() {
 }
 
 void DiskBasedCertCache::ReadWorker::Finish(int rv) {
-  cleanup_callback_.Run();
+  cleanup_callback_.Run(cert_handle_);
   cleanup_callback_.Reset();
   RunCallbacks();
   delete this;
@@ -475,7 +471,11 @@ DiskBasedCertCache::ReadWorker::~ReadWorker() {
 }
 
 DiskBasedCertCache::DiskBasedCertCache(disk_cache::Backend* backend)
-    : backend_(backend), weak_factory_(this) {
+    : backend_(backend),
+      mru_cert_cache_(kMemoryCacheMaxSize),
+      mem_cache_hits_(0),
+      mem_cache_misses_(0),
+      weak_factory_(this) {
   DCHECK(backend_);
 }
 
@@ -495,6 +495,17 @@ DiskBasedCertCache::~DiskBasedCertCache() {
 void DiskBasedCertCache::Get(const std::string& key, const GetCallback& cb) {
   DCHECK(!key.empty());
 
+  // If the handle is already in the MRU cache, just return that (via callback).
+  // Note, this will also bring the cert_handle to the front

[wtc, 2014/07/02 20:51:50]

Nit: this line break is too short.

+  // of the recency list in the MRU cache.
+  MRUCertCache::iterator mru_it = mru_cert_cache_.Get(key);
+  if (mru_it != mru_cert_cache_.end()) {
+    ++mem_cache_hits_;
+    cb.Run(mru_it->second);
+    return;

[rvargas (doing something else), 2014/07/02 22:14:38]

You may want to tell the backend about this: backend_->OnExternalCacheHit()

+  }
+  ++mem_cache_misses_;
+
   ReadWorkerMap::iterator it = read_worker_map_.find(key);
 
   if (it == read_worker_map_.end()) {
@@ -518,6 +529,16 @@ void DiskBasedCertCache::Set(const X509Certificate::OSCertHandle cert_handle,
   DCHECK(cert_handle);
   std::string key = GetCacheKeyToCert(cert_handle);
 
+  // If |cert_handle| already exists in the MRU cache, there is no need to
+  // re-write it to the disk cache. This will also bring |cert_handle|
+  // to the front of the recency list in the MRU cache.
+  if (mru_cert_cache_.Get(key) != mru_cert_cache_.end()) {
+    ++mem_cache_hits_;
+    cb.Run(key);
+    return;
+  }
+  ++mem_cache_misses_;

[wtc, 2014/07/02 20:51:50]

IMPORTANT: We should think about whether Set() should be satisfied by the
in-memory cache.

Consider this case: for some reason, a certificate is evicted from the disk
cache, but it is still in the in-memory cache.

When the next Set() call comes in, it will be satisfied by the in-memory cache.
But the caller of Set() may expect that the cert is persisted to the disk.

Can this case happen?

[Ryan Sleevi, 2014/07/02 21:49:58]

Yes.

I think we only want Get to be satisfied by the cache. Set should add to the
cache.

+
   WriteWorkerMap::iterator it = write_worker_map_.find(key);
 
   if (it == write_worker_map_.end()) {
@@ -527,7 +548,8 @@ void DiskBasedCertCache::Set(const X509Certificate::OSCertHandle cert_handle,
                         cert_handle,
                         base::Bind(&DiskBasedCertCache::FinishedWriteOperation,
                                    weak_factory_.GetWeakPtr(),
-                                   key));
+                                   key,
+                                   cert_handle));
     write_worker_map_[key] = worker;
     worker->AddCallback(cb);
     worker->Start();
@@ -536,11 +558,19 @@ void DiskBasedCertCache::Set(const X509Certificate::OSCertHandle cert_handle,
   }
 }
 
-void DiskBasedCertCache::FinishedWriteOperation(const std::string& key) {
+void DiskBasedCertCache::FinishedWriteOperation(
+    const std::string& key,
+    X509Certificate::OSCertHandle cert_handle) {
   write_worker_map_.erase(key);
+  if (key != std::string())

[wtc, 2014/07/02 20:51:49]

Test !key.empty().

+    mru_cert_cache_.Put(key, X509Certificate::DupOSCertHandle(cert_handle));
 }
 
-void DiskBasedCertCache::FinishedReadOperation(const std::string& key) {
+void DiskBasedCertCache::FinishedReadOperation(
+    const std::string& key,
+    X509Certificate::OSCertHandle cert_handle) {
+  if (cert_handle)
+    mru_cert_cache_.Put(key, X509Certificate::DupOSCertHandle(cert_handle));
   read_worker_map_.erase(key);
 }