Fixes the cache lock issue.

net/http/http_cache_shared_writers_unittest.cc

+// Copyright (c) 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/http/http_cache_transaction.h"
+#include "net/http/http_transaction.h"
+#include "net/http/http_transaction_test_util.h"
+#include "net/http/mock_http_cache.h"
+#include "net/test/gtest_util.h"
+
+using net::test::IsError;
+using net::test::IsOk;
+
+namespace net {
+
+namespace {
+
+// helpers
+void ReadAndVerifyTransaction(HttpTransaction* transaction,
+                              const MockTransaction& transaction_info) {
+  std::string content;
+  int rv = ReadTransaction(transaction, &content);
+
+  EXPECT_THAT(rv, IsOk());
+  std::string expected(transaction_info.data);
+  EXPECT_EQ(expected, content);
+}
+
+// The 1st transaction reads from the network and the subsequent transactions
+// are able to read from the cache even before the complete response is written
+// to the cache.
+int ReadSharedWritersCacheRead(std::vector<Context*>& context_list,
+                               std::vector<std::string>& results) {
+  int rv;
+
+  size_t i = 0;
+  HttpTransaction* transaction = nullptr;
+  do {
+    Context* c = context_list.at(i);
+    transaction = c->trans.get();
+    scoped_refptr<IOBuffer> buf(new IOBuffer(256));
+    rv = transaction->Read(buf.get(), 256, c->callback.callback());
+    if (rv == ERR_IO_PENDING)
+      rv = c->callback.WaitForResult();
+
+    if (rv > 0)
+      results.at(i).append(buf->data(), rv);
+    else if (rv < 0)
+      return rv;
+
+    i = (i == context_list.size() - 1) ? 0 : i + 1;
+  } while (rv > 0);
+
+  return OK;
+}
+
+void ReadAndVerifySharedWritersCacheRead(
+    std::vector<Context*>& context_list,
+    const MockTransaction& transaction_info) {
+  std::vector<std::string> contents(context_list.size());
+  int rv = ReadSharedWritersCacheRead(context_list, contents);
+
+  EXPECT_THAT(rv, IsOk());
+  std::string expected(transaction_info.data);
+  for (size_t i = 0; i < contents.size(); i++) {
+    EXPECT_EQ(expected, contents.at(i));
+  }
+}
+
+// The 1st transaction reads from the network and read is invoked on other
+// transactions even before the 1st one's io callback is invoked. The other
+// transactions should have data written in their read buffers as part
+// of the 1st transaction's callback.
+int ReadSharedWritersJoinedRead(std::vector<Context*>& context_list,
+                                std::vector<std::string>& results) {
+  int rv = 0;
+  do {
+    // Invoke Read for all transactions.
+    std::vector<scoped_refptr<IOBuffer>> buffers(context_list.size());
+    for (size_t i = 0; i < context_list.size(); i++) {
+      HttpTransaction* transaction = context_list[i]->trans.get();
+      buffers[i] = new IOBuffer(30);
+      rv = transaction->Read(buffers[i].get(), 30,
+                             context_list[i]->callback.callback());
+      // Invoking stop caching here should not have any impact since there are
+      // multiple transactions waiting for this resource.
+      if (i == 0)
+        transaction->StopCaching();
+    }
+    if (rv == ERR_IO_PENDING) {
+      for (size_t i = 0; i < context_list.size(); i++) {
+        Context* ct = context_list[i];
+        rv = ct->callback.WaitForResult();
+      }
+    }
+
+    if (rv > 0) {
+      for (size_t i = 0; i < results.size(); i++) {
+        results[i].append(buffers[i]->data(), rv);
+      }
+    } else if (rv < 0) {
+      return rv;
+    }
+  } while (rv > 0);
+
+  return OK;
+}
+
+void ReadAndVerifySharedWritersJoinedRead(
+    const MockTransaction& transaction_info,
+    std::vector<Context*>& context_list) {
+  std::vector<std::string> results(context_list.size());
+  int rv = ReadSharedWritersJoinedRead(context_list, results);
+
+  EXPECT_THAT(rv, IsOk());
+  std::string expected(transaction_info.data);
+  for (size_t i = 0; i < results.size(); i++) {
+    EXPECT_EQ(expected, results[i]);
+  }
+}
+
+int ReadSharedWritersJoinedReadDoneReading(std::vector<Context*>& context_list,
+                                           std::vector<std::string>& results) {
+  int rv = 0;
+  int cnt = 0;
+  do {
+    // Invoke Read for all transactions.
+    std::vector<scoped_refptr<IOBuffer>> buffers(context_list.size());
+    for (size_t i = 0; i < context_list.size(); i++) {
+      HttpTransaction* transaction = context_list[i]->trans.get();
+      buffers[i] = new IOBuffer(30);
+      rv = transaction->Read(buffers[i].get(), 30,
+                             context_list[i]->callback.callback());
+    }
+    if (rv == ERR_IO_PENDING) {
+      for (size_t i = 0; i < context_list.size(); i++) {
+        Context* ct = context_list[i];
+        rv = ct->callback.WaitForResult();
+      }
+    }
+
+    if (rv > 0) {
+      for (size_t i = 0; i < results.size(); i++) {
+        results[i].append(buffers[i]->data(), rv);
+      }
+    } else if (rv < 0) {
+      return rv;
+    }
+
+    cnt++;
+    if (cnt == 2) {
+      context_list[0]->trans.get()->DoneReading();
+    }
+  } while (cnt < 2);
+
+  return OK;
+}
+
+void ReadAndVerifySharedWritersJoinedReadDoneReading(
+    const MockTransaction& transaction_info,
+    std::vector<Context*>& context_list) {
+  std::vector<std::string> results(context_list.size());
+  int rv = ReadSharedWritersJoinedReadDoneReading(context_list, results);
+
+  EXPECT_THAT(rv, IsOk());
+  std::string expected(transaction_info.data);
+  for (size_t i = 0; i < results.size(); i++) {
+    EXPECT_EQ(expected, results[i]);
+  }
+}
+
+// The 1st transaction reads from the network and read is invoked on other
+// transactions even before the 1st one's io callback is invoked. Also, the
+// first transaction is deleted before the io callback is invoked. The other
+// transactions should have data written in their read buffers as part
+// of the 1st transaction's callback.
+int ReadSharedWritersJoinedReadDeleteCurrentWriter(
+    std::vector<Context*>& context_list,
+    std::vector<std::string>& results) {
+  int rv = 0;
+  bool first_iter = true;
+  do {
+    // Invoke Read for all transactions.
+    std::vector<scoped_refptr<IOBuffer>> buffers(context_list.size());
+    for (size_t i = 0; i < context_list.size(); i++) {
+      HttpTransaction* transaction = context_list[i]->trans.get();
+      buffers[i] = new IOBuffer(30);
+      rv = transaction->Read(buffers[i].get(), 30,
+                             context_list[i]->callback.callback());
+    }
+
+    // Delete the 1st transaction.
+    if (first_iter) {
+      Context* c = context_list[0];
+      context_list.erase(context_list.begin());
+      delete c;
+      buffers.erase(buffers.begin());
+    }
+
+    if (rv == ERR_IO_PENDING) {
+      for (size_t i = 0; i < context_list.size(); i++) {
+        Context* ct = context_list[i];
+        rv = ct->callback.WaitForResult();
+      }
+    }
+
+    if (rv > 0) {
+      for (size_t i = 0; i < context_list.size(); i++) {
+        results[i].append(buffers[i]->data(), rv);
+      }
+    } else if (rv < 0) {
+      return rv;
+    }
+
+    first_iter = false;
+  } while (rv > 0);
+
+  return OK;
+}
+
+void ReadAndVerifySharedWritersJoinedReadDeleteCurrentWriter(
+    const MockTransaction& transaction_info,
+    std::vector<Context*>& context_list) {
+  std::vector<std::string> results(context_list.size() - 1);
+  int rv =
+      ReadSharedWritersJoinedReadDeleteCurrentWriter(context_list, results);
+
+  EXPECT_THAT(rv, IsOk());
+  std::string expected(transaction_info.data);
+  for (size_t i = 0; i < results.size(); i++) {
+    EXPECT_EQ(expected, results[i]);
+  }
+}
+
+int ReadSharedWritersJoinedReadDeleteWaitingWriter(
+    std::vector<Context*>& context_list,
+    std::vector<std::string>& results) {
+  int rv = 0;
+  bool first_iter = true;
+  do {
+    // Invoke Read for all transactions.
+    std::vector<scoped_refptr<IOBuffer>> buffers(context_list.size());
+    for (size_t i = 0; i < context_list.size(); i++) {
+      HttpTransaction* transaction = context_list[i]->trans.get();
+      buffers[i] = new IOBuffer(30);
+      rv = transaction->Read(buffers[i].get(), 30,
+                             context_list[i]->callback.callback());
+    }
+
+    // Remove a waiting writer transaction.
+    if (first_iter) {
+      auto it = context_list.begin();
+      it++;
+      if (it != context_list.end()) {
+        Context* c = *it;
+        context_list.erase(it);
+        delete c;
+        auto it1 = buffers.begin();
+        it1++;
+        buffers.erase(it1);
+      }
+    }
+
+    if (rv == ERR_IO_PENDING) {
+      for (size_t i = 0; i < context_list.size(); i++) {
+        Context* ct = context_list[i];
+        rv = ct->callback.WaitForResult();
+      }
+    }
+
+    if (rv > 0) {
+      for (size_t i = 0; i < context_list.size(); i++) {
+        results[i].append(buffers[i]->data(), rv);
+      }
+    } else if (rv < 0) {
+      return rv;
+    }
+
+    first_iter = false;
+  } while (rv > 0);
+
+  return OK;
+}
+
+void ReadAndVerifySharedWritersDeleteWaitingWriter(
+    const MockTransaction& transaction_info,
+    std::vector<Context*>& context_list) {
+  std::vector<std::string> results(context_list.size() - 1);
+  int rv =
+      ReadSharedWritersJoinedReadDeleteWaitingWriter(context_list, results);
+
+  EXPECT_THAT(rv, IsOk());
+  std::string expected(transaction_info.data);
+  for (size_t i = 0; i < results.size(); i++) {
+    EXPECT_EQ(expected, results[i]);
+  }
+}
+
+int ReadSharedWritersJoinedReadDeleteIdleWriter(
+    std::vector<Context*>& context_list,
+    std::vector<std::string>& results) {
+  int rv = 0;
+  bool first_iter = true;
+  do {
+    // Invoke Read for all transactions.
+    std::vector<scoped_refptr<IOBuffer>> buffers(context_list.size());
+    for (size_t i = 0; i < context_list.size(); i++) {
+      HttpTransaction* transaction = context_list[i]->trans.get();
+      buffers[i] = new IOBuffer(30);
+      // Do not invoke Read on the first transaction.
+      if (first_iter && i == 0)
+        continue;
+      rv = transaction->Read(buffers[i].get(), 30,
+                             context_list[i]->callback.callback());
+    }
+
+    // Remove the idle writer transaction.
+    if (first_iter) {
+      auto it = context_list.begin();
+      Context* c = *it;
+      context_list.erase(it);
+      delete c;
+      auto it1 = buffers.begin();
+      buffers.erase(it1);
+    }
+
+    if (rv == ERR_IO_PENDING) {
+      for (size_t i = 0; i < context_list.size(); i++) {
+        Context* ct = context_list[i];
+        rv = ct->callback.WaitForResult();
+      }
+    }
+
+    if (rv > 0) {
+      for (size_t i = 0; i < context_list.size(); i++) {
+        results[i].append(buffers[i]->data(), rv);
+      }
+    } else if (rv < 0) {
+      return rv;
+    }
+
+    first_iter = false;
+  } while (rv > 0);
+
+  return OK;
+}
+
+void ReadAndVerifySharedWritersDeleteIdleWriter(
+    const MockTransaction& transaction_info,
+    std::vector<Context*>& context_list) {
+  std::vector<std::string> results(context_list.size() - 1);
+  int rv = ReadSharedWritersJoinedReadDeleteIdleWriter(context_list, results);
+
+  EXPECT_THAT(rv, IsOk());
+  std::string expected(transaction_info.data);
+  for (size_t i = 0; i < results.size(); i++) {
+    EXPECT_EQ(expected, results[i]);
+  }
+}
+
+int ReadSharedWritersJoinedReadCacheWriteFailure(
+    std::vector<Context*>& context_list,
+    std::vector<std::string>& results,
+    MockHttpCache& cache) {
+  int rv = 0;
+  MockHttpRequest request(kSimpleGET_Transaction);
+
+  // Fail the request.
+  cache.disk_cache()->set_soft_failures(true);
+
+  // We have to open the entry again to propagate the failure flag.
+  disk_cache::Entry* en;
+  cache.OpenBackendEntry(kSimpleGET_Transaction.url, &en);
+  en->Close();
+
+  // Invoke Read for two transactions so they become current_writer_ and
+  // waiting_writers_ respectively.
+  std::vector<scoped_refptr<IOBuffer>> buf(2);
+  size_t i = 0, j = 0;
+  do {
+    HttpTransaction* transaction = context_list[i]->trans.get();
+    buf[j] = new IOBuffer(30);
+    rv = transaction->Read(buf[j].get(), 30,
+                           context_list[i]->callback.callback());
+    i = context_list.size() - 1;
+    j++;
+  } while (j < buf.size());
+
+  // current_writer_ which is transaction [0] should continue without writing
+  // to the cache, idle writer ([3]) should fail on its next Read call and
+  // waiting_writers_ ([6]) should return a failure back.
+  if (rv == ERR_IO_PENDING) {
+    Context* ct = *(context_list.begin());
+    rv = ct->callback.WaitForResult();
+  }
+
+  // Only [0] should succeed in the Read.
+  results[0].append(buf[0]->data(), 30);
+
+  // Invoke Start on 4 and 5. 4 will fail to read from the cache, doom the
+  // entry and go on to create a new entry. 5 will also get added to that
+  // entry.
+  for (size_t i = 4; i <= 5; i++) {
+    Context* c = context_list[i];
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+  }
+
+  base::RunLoop().RunUntilIdle();
+
+  // 3 and 6 failed, delete them.
+  Context* c = context_list[3];
+  scoped_refptr<IOBuffer> buf1 = new IOBuffer(30);
+  int rv_fail = c->trans->Read(buf1.get(), 30, c->callback.callback());
+  EXPECT_THAT(rv_fail, ERR_CACHE_WRITE_FAILURE);
+
+  Context* c6 = context_list[6];
+  for (auto itr = context_list.begin(); itr != context_list.end();) {
+    if (*itr == c || *itr == c6) {
+      Context* ct = *itr;
+      itr = context_list.erase(itr);
+      delete ct;
+    } else {
+      itr++;
+    }
+  }
+
+  cache.disk_cache()->set_soft_failures(false);
+
+  base::RunLoop().RunUntilIdle();
+
+  // Read for the rest of the transactions.
+  Context* c0 = context_list[0];
+  Context* c3 = context_list[3];
+  for (size_t i = 0; i < context_list.size(); i++) {
+    if (i == 1 || i == 2 || i == 4)
+      continue;
+    std::string res;
+    ReadTransaction(context_list[i]->trans.get(), &res);
+    results[i].append(res);
+  }
+
+  base::RunLoop().RunUntilIdle();
+
+  // Delete the done transactions so that pending queue can be processed.
+  // The reader transactions will error out with ERR_CACHE_MISS because of cache
+  // failures.
+  Context* c1 = context_list[1];
+  Context* c2 = context_list[2];
+  auto itr = context_list.begin();
+  for (; itr != context_list.end();) {
+    Context* c = *itr;
+    if (c == c0 || c == c1 || c == c2 || c == c3) {
+      itr = context_list.erase(itr);
+      delete c;
+    } else {
+      itr++;
+    }
+  }
+
+  std::string res;
+  ReadTransaction(context_list[0]->trans.get(), &res);
+  results[4].append(res);
+
+  return OK;
+}
+
+void ReadAndVerifySharedWritersJoinedReadCacheWriteFailure(
+    const MockTransaction& transaction_info,
+    std::vector<Context*>& context_list,
+    MockHttpCache& cache) {
+  std::vector<std::string> results(context_list.size());
+  int rv = ReadSharedWritersJoinedReadCacheWriteFailure(context_list, results,
+                                                        cache);
+
+  EXPECT_THAT(rv, IsOk());
+  std::string expected(transaction_info.data);
+  for (size_t i = 0; i < context_list.size(); i++) {
+    EXPECT_EQ(expected, results[i]);
+  }
+}
+
+}  // namespace
+
+// Tests.
+
+TEST(HttpCache, SimpleGET_SharedWritingCacheRead) {
+  MockHttpCache cache;
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+
+  std::vector<Context*> context_list;
+  const int kNumTransactions = 5;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(new Context());
+    Context* c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+  }
+
+  // All requests are waiting for the active entry.
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE, c->trans->GetLoadState());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  // The first request should be a writer at this point, and the subsequent
+  // requests should be pending.
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  // All requests depend on the writer, and the writer is between Start and
+  // Read, i.e. idle.
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+  }
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    if (c->result == ERR_IO_PENDING)
+      c->result = c->callback.WaitForResult();
+  }
+
+  ReadAndVerifySharedWritersCacheRead(context_list, kSimpleGET_Transaction);
+
+  // We should not have had to re-open the disk entry
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    delete c;
+  }
+}
+
+TEST(HttpCache, SimpleGET_SharedWritingJoinedRead) {
+  MockHttpCache cache;
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+
+  std::vector<Context*> context_list;
+  const int kNumTransactions = 5;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(new Context());
+    Context* c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+  }
+
+  // All requests are waiting for the active entry.
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE, c->trans->GetLoadState());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  // The first request should be a writer at this point, and the subsequent
+  // requests should be pending.
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+  // All requests depend on the writer, and the writer is between Start and
+  // Read, i.e. idle.
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+  }
+
+  std::vector<HttpTransaction*> transactions;
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    if (c->result == ERR_IO_PENDING)
+      c->result = c->callback.WaitForResult();
+    transactions.push_back(c->trans.get());
+  }
+
+  ReadAndVerifySharedWritersJoinedRead(kSimpleGET_Transaction, context_list);
+
+  // We should not have had to re-open the disk entry
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    delete c;
+  }
+}
+
+TEST(HttpCache, SimpleGET_SharedWritingJoinedReadDoneReading) {
+  MockHttpCache cache;
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+
+  std::vector<Context*> context_list;
+  const int kNumTransactions = 5;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(new Context());
+    Context* c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+  }
+
+  // All requests are waiting for the active entry.
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE, c->trans->GetLoadState());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  // The first request should be a writer at this point, and the subsequent
+  // requests should be pending.
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  // All requests depend on the writer, and the writer is between Start and
+  // Read, i.e. idle.
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+  }
+
+  std::vector<HttpTransaction*> transactions;
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    if (c->result == ERR_IO_PENDING)
+      c->result = c->callback.WaitForResult();
+    transactions.push_back(c->trans.get());
+  }
+
+  ReadAndVerifySharedWritersJoinedReadDoneReading(kSimpleGET_Transaction,
+                                                  context_list);
+
+  // We should not have had to re-open the disk entry
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    delete c;
+  }
+}
+
+// Tests the following:
+// - A 200 will doom the entry and the transaction will continue to read from
+// the network.
+// - Doomed entry's SharedWriters will continue to read and write to the cache.
+// - Doomed entry's SharedWriters' waiting_for_validation_ will create another
+// entry.
+// - The new entry will also have another SharedWriters for subsequent
+// transactions.
+TEST(HttpCache, SharedWritingValidation200) {
+  MockHttpCache cache;
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+  request.load_flags |= LOAD_VALIDATE_CACHE;
+  MockHttpRequest reader_request(kSimpleGET_Transaction);
+  reader_request.load_flags = LOAD_ONLY_FROM_CACHE | LOAD_SKIP_CACHE_VALIDATION;
+  MockHttpRequest request_no_validate(kSimpleGET_Transaction);
+
+  std::vector<Context*> context_list;
+  const int kNumTransactions = 6;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(new Context());
+    Context* c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    MockHttpRequest* this_request = &request;
+    if (i == 1 || i == 2)
+      this_request = &reader_request;
+
+    if (i == 5)
+      this_request = &request_no_validate;
+
+    c->result = c->trans->Start(this_request, c->callback.callback(),
+                                NetLogWithSource());
+  }
+
+  // All requests are waiting for the active entry.
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE, c->trans->GetLoadState());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  // The first [0] request should be a writer at this point, and should have
+  // created
+  // SharedWriters, [1] and [2] will be in pending_queue and [3] and [4] should
+  // have validated and [5] will have skipped validation and be ready to read.
+
+  EXPECT_EQ(3, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(2, cache.disk_cache()->create_count());
+
+  Context* c = context_list[0];
+  ASSERT_THAT(c->result, IsError(ERR_IO_PENDING));
+  c->result = c->callback.WaitForResult();
+
+  // First request is done with the headers, now [3] will start validation.
+  Context* c3 = context_list[3];
+  ASSERT_THAT(c3->result, IsError(ERR_IO_PENDING));
+
+  // Let [3] get a 200 , thus leading to dooming the entry, [4] and [5] will
+  // move to entry's pending_queue.
+  c3->result = c3->callback.WaitForResult();
+
+  // [3] will complete reading the response using its own network transaction
+  // and not writing to the cache.
+  ReadAndVerifyTransaction(c3->trans.get(), kSimpleGET_Transaction);
+
+  // [0] will complete reading the response using SharedWriter's network
+  // transaction and then the entry should be finalized.
+  ReadAndVerifyTransaction(c->trans.get(), kSimpleGET_Transaction);
+
+  // [4] should be added to a new entry and should contiue reading and writing
+  // to the cache (also create SharedWriters)
+  for (int i = 4; i <= 5; i++) {
+    Context* c = context_list[i];
+    ASSERT_THAT(c->result, IsError(ERR_IO_PENDING));
+    c->result = c->callback.WaitForResult();
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+    // [5] will join SharedWriters at this point when [4] completes validation.
+    ReadAndVerifyTransaction(c->trans.get(), kSimpleGET_Transaction);
+  }
+  // [1] and [2] will become readers and read from the cache.
+  for (int i = 1; i <= 2; i++) {
+    Context* c = context_list[i];
+    ASSERT_THAT(c->result, IsError(ERR_IO_PENDING));
+    c->result = c->callback.WaitForResult();
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+    ReadAndVerifyTransaction(c->trans.get(), kSimpleGET_Transaction);
+  }
+
+  // We should not have had to re-open the disk entry
+  EXPECT_EQ(3, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(2, cache.disk_cache()->create_count());
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    delete c;
+  }
+}
+
+// Tests a validating transaction deletion while it is waiting for its callback
+// to be invoked.
+TEST(HttpCache, SharedWritingDeleteValidationTrans) {
+  MockHttpCache cache;
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+  request.load_flags |= LOAD_VALIDATE_CACHE;
+  MockHttpRequest reader_request(kSimpleGET_Transaction);
+  reader_request.load_flags = LOAD_ONLY_FROM_CACHE | LOAD_SKIP_CACHE_VALIDATION;
+
+  std::vector<Context*> context_list;
+  const int kNumTransactions = 5;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(new Context());
+    Context* c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    MockHttpRequest* this_request = &request;
+    if (i == 1 || i == 2)
+      this_request = &reader_request;
+
+    if (i == 3 || i == 4)
+      continue;
+
+    c->result = c->trans->Start(this_request, c->callback.callback(),
+                                NetLogWithSource());
+  }
+
+  // All requests are waiting for the active entry.
+  for (int i = 0; i < kNumTransactions; ++i) {
+    if (i == 3 || i == 4)
+      continue;
+    Context* c = context_list[i];
+    EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE, c->trans->GetLoadState());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  // Start [3], [4].
+  for (size_t i = 3; i <= 4; i++) {
+    Context* c = context_list[i];
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+    ASSERT_THAT(c->result, IsError(ERR_IO_PENDING));
+  }
+
+  // Delete [3] as it is the current validating trans.
+  Context* c3 = context_list[3];
+  for (auto it = context_list.begin(); it != context_list.end(); it++) {
+    if (*it == c3) {
+      context_list.erase(it);
+      delete c3;
+      break;
+    }
+  }
+
+  // Complete start state machine for [4].
+  base::RunLoop().RunUntilIdle();
+
+  // [0] will complete reading the response using SharedWriter's network
+  // transaction and then the entry should be finalized.
+  Context* c0 = context_list[0];
+  ReadAndVerifyTransaction(c0->trans.get(), kSimpleGET_Transaction);
+
+  // [4] (now [3]) should doom the entry and continue reading with its network
+  // transaction.
+  Context* c4 = context_list[3];
+  ReadAndVerifyTransaction(c4->trans.get(), kSimpleGET_Transaction);
+
+  // 1st entry will get destroyed and [1] and [2] will being readers will get a
+  // ERR_CACHE_MISS.
+  for (int i = 1; i <= 2; i++) {
+    Context* c = context_list[i];
+    ASSERT_THAT(c->result, IsError(ERR_IO_PENDING));
+    c->result = c->callback.WaitForResult();
+    ASSERT_THAT(c->result, IsError(ERR_CACHE_MISS));
+  }
+
+  // We should not have had to re-open the disk entry
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  for (auto i = context_list.begin(); i != context_list.end(); ++i) {
+    Context* c = *i;
+    delete c;
+  }
+}
+
+// Tests a transaction deletion while it is waiting for validation.
+TEST(HttpCache, SharedWritingDeleteWaitingForValidation) {
+  MockHttpCache cache;
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+  request.load_flags |= LOAD_VALIDATE_CACHE;
+  MockHttpRequest reader_request(kSimpleGET_Transaction);
+  reader_request.load_flags = LOAD_ONLY_FROM_CACHE | LOAD_SKIP_CACHE_VALIDATION;
+
+  std::vector<Context*> context_list;
+  const int kNumTransactions = 5;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(new Context());
+    Context* c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    MockHttpRequest* this_request = &request;
+    if (i == 1 || i == 2)
+      this_request = &reader_request;
+
+    if (i == 3 || i == 4)
+      continue;
+
+    c->result = c->trans->Start(this_request, c->callback.callback(),
+                                NetLogWithSource());
+  }
+
+  // All requests are waiting for the active entry.
+  for (int i = 0; i < kNumTransactions; ++i) {
+    if (i == 3 || i == 4)
+      continue;
+    Context* c = context_list[i];
+    EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE, c->trans->GetLoadState());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  // Start [3], [4].
+  for (size_t i = 3; i <= 4; i++) {
+    Context* c = context_list[i];
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+    ASSERT_THAT(c->result, IsError(ERR_IO_PENDING));
+  }
+
+  // Delete [4] as it is the waiting for validation trans.
+  Context* c4 = context_list[4];
+  for (auto it = context_list.begin(); it != context_list.end(); it++) {
+    if (*it == c4) {
+      context_list.erase(it);
+      delete c4;
+      break;
+    }
+  }
+
+  // Complete start state machine for [3].
+  base::RunLoop().RunUntilIdle();
+
+  // [0] will complete reading the response using SharedWriter's network
+  // transaction and then the entry should be finalized.
+  Context* c0 = context_list[0];
+  ReadAndVerifyTransaction(c0->trans.get(), kSimpleGET_Transaction);
+
+  // [3] should doom the entry and continue reading with its network
+  // transaction.
+  Context* c3 = context_list[3];
+  ReadAndVerifyTransaction(c3->trans.get(), kSimpleGET_Transaction);
+
+  // 1st entry will get destroyed and [1] and [2] will being readers will get a
+  // ERR_CACHE_MISS.
+  for (int i = 1; i <= 2; i++) {
+    Context* c = context_list[i];
+    ASSERT_THAT(c->result, IsError(ERR_IO_PENDING));
+    c->result = c->callback.WaitForResult();
+    ASSERT_THAT(c->result, IsError(ERR_CACHE_MISS));
+  }
+
+  // We should not have had to re-open the disk entry
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  for (auto i = context_list.begin(); i != context_list.end(); ++i) {
+    Context* c = *i;
+    delete c;
+  }
+}
+
+// Tests the impact of cache write failure on Shared Writing.
+TEST(HttpCache, SharedWritingCacheWriteFailure) {
+  MockHttpCache cache;
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+  request.load_flags |= LOAD_VALIDATE_CACHE;
+  MockHttpRequest reader_request(kSimpleGET_Transaction);
+  reader_request.load_flags = LOAD_ONLY_FROM_CACHE | LOAD_SKIP_CACHE_VALIDATION;
+  MockHttpRequest request_no_validate(kSimpleGET_Transaction);
+
+  std::vector<Context*> context_list;
+  const int kNumTransactions = 7;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(new Context());
+    Context* c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    MockHttpRequest* this_request = &request;
+    if (i == 1 || i == 2)
+      this_request = &reader_request;
+
+    if (i == 3 || i == 6)
+      this_request = &request_no_validate;
+
+    if (i == 4 || i == 5)
+      continue;
+
+    c->result = c->trans->Start(this_request, c->callback.callback(),
+                                NetLogWithSource());
+  }
+
+  // All requests are waiting for the active entry.
+  for (int i = 0; i < kNumTransactions; ++i) {
+    if (i == 4 || i == 5)
+      continue;
+    Context* c = context_list[i];
+    EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE, c->trans->GetLoadState());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  // At this point, 0,5 and 3 are idle writers, 1 and 2 are pending readers and
+  // 4
+  // will now become the validating_trans_.
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  ReadAndVerifySharedWritersJoinedReadCacheWriteFailure(kSimpleGET_Transaction,
+                                                        context_list, cache);
+
+  // We should not have had to re-open the disk entry
+  EXPECT_EQ(3, cache.network_layer()->transaction_count());
+  EXPECT_EQ(1, cache.disk_cache()->open_count());
+  EXPECT_EQ(3, cache.disk_cache()->create_count());
+
+  for (auto i = context_list.begin(); i != context_list.end(); ++i) {
+    Context* c = *i;
+    delete c;
+  }
+}
+
+TEST(HttpCache, SimpleGET_SharedWritingJoinedReadDeleteCurrentWriter) {
+  MockHttpCache cache;
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+
+  std::vector<Context*> context_list;
+  const int kNumTransactions = 5;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(new Context());
+    Context* c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+  }
+
+  // All requests are waiting for the active entry.
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE, c->trans->GetLoadState());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  // The first request should be a writer at this point, and the subsequent
+  // requests should be pending.
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  // All requests depend on the writer, and the writer is between Start and
+  // Read, i.e. idle.
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+  }
+
+  std::vector<HttpTransaction*> transactions;
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    if (c->result == ERR_IO_PENDING)
+      c->result = c->callback.WaitForResult();
+    transactions.push_back(c->trans.get());
+  }
+
+  ReadAndVerifySharedWritersJoinedReadDeleteCurrentWriter(
+      kSimpleGET_Transaction, context_list);
+
+  // We should not have had to re-open the disk entry
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  for (auto i = context_list.begin(); i != context_list.end(); ++i) {
+    Context* c = *i;
+    delete c;
+  }
+}
+
+TEST(HttpCache, SimpleGET_SharedWritingJoinedReadDeleteWaitingWriter) {
+  MockHttpCache cache;
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+
+  std::vector<Context*> context_list;
+  const int kNumTransactions = 5;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(new Context());
+    Context* c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+  }
+
+  // All requests are waiting for the active entry.
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE, c->trans->GetLoadState());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  // The first request should be a writer at this point, and the subsequent
+  // requests should be pending.
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  // All requests depend on the writer, and the writer is between Start and
+  // Read, i.e. idle.
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+  }
+
+  std::vector<HttpTransaction*> transactions;
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    if (c->result == ERR_IO_PENDING)
+      c->result = c->callback.WaitForResult();
+    transactions.push_back(c->trans.get());
+  }
+
+  ReadAndVerifySharedWritersDeleteWaitingWriter(kSimpleGET_Transaction,
+                                                context_list);
+
+  // We should not have had to re-open the disk entry
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  for (auto i = context_list.begin(); i != context_list.end(); ++i) {
+    Context* c = *i;
+    delete c;
+  }
+}
+
+TEST(HttpCache, SimpleGET_SharedWritingJoinedReadDeleteIdleWriter) {
+  MockHttpCache cache;
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+
+  std::vector<Context*> context_list;
+  const int kNumTransactions = 5;
+
+  for (int i = 0; i < kNumTransactions; ++i) {
+    context_list.push_back(new Context());
+    Context* c = context_list[i];
+
+    c->result = cache.CreateTransaction(&c->trans);
+    ASSERT_THAT(c->result, IsOk());
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+
+    c->result =
+        c->trans->Start(&request, c->callback.callback(), NetLogWithSource());
+  }
+
+  // All requests are waiting for the active entry.
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    EXPECT_EQ(LOAD_STATE_WAITING_FOR_CACHE, c->trans->GetLoadState());
+  }
+
+  // Allow all requests to move from the Create queue to the active entry.
+  base::RunLoop().RunUntilIdle();
+
+  // The first request should be a writer at this point, and the subsequent
+  // requests should be pending.
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  // All requests depend on the writer, and the writer is between Start and
+  // Read, i.e. idle.
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    EXPECT_EQ(LOAD_STATE_IDLE, c->trans->GetLoadState());
+  }
+
+  std::vector<HttpTransaction*> transactions;
+  for (int i = 0; i < kNumTransactions; ++i) {
+    Context* c = context_list[i];
+    if (c->result == ERR_IO_PENDING)
+      c->result = c->callback.WaitForResult();
+    transactions.push_back(c->trans.get());
+  }
+
+  ReadAndVerifySharedWritersDeleteIdleWriter(kSimpleGET_Transaction,
+                                             context_list);
+  // We should not have had to re-open the disk entry
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  for (auto i = context_list.begin(); i != context_list.end(); ++i) {
+    Context* c = *i;
+    delete c;
+  }
+}
+
+}  // namespace net