Add MinidumpThreadListWriter::InitializeFromSnapshot()

minidump/minidump_thread_id_map.cc

Index: minidump/minidump_thread_id_map.cc
diff --git a/minidump/minidump_thread_id_map.cc b/minidump/minidump_thread_id_map.cc
new file mode 100644
index 0000000000000000000000000000000000000000..919566f5d05623ee5c73adce29de1b7d76c4b9fe
--- /dev/null
+++ b/minidump/minidump_thread_id_map.cc
@@ -0,0 +1,66 @@
+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "minidump/minidump_thread_id_map.h"
+
+#include <limits>
+#include <set>
+#include <utility>
+
+#include "base/logging.h"
+#include "snapshot/thread_snapshot.h"
+
+namespace crashpad {
+
+void BuildMinidumpThreadIDMap(
+    const std::vector<const ThreadSnapshot*>& thread_snapshots,
+    MinidumpThreadIDMap* thread_id_map) {
+  DCHECK(thread_id_map->empty());
+
+  // First, try truncating each 64-bit thread ID to 32 bits. If that’s possible
+  // for each unique 64-bit thread ID, then this will be used as the mapping.
+  // This preserves as much of the original thread ID as possible when feasible.
+  bool collision = false;
+  std::set<uint32_t> thread_ids_32;
+  for (const ThreadSnapshot* thread_snapshot : thread_snapshots) {
+    uint64_t thread_id_64 = thread_snapshot->ThreadID();
+    if (thread_id_map->find(thread_id_64) == thread_id_map->end()) {
+      uint32_t thread_id_32 = thread_id_64;
+      if (thread_ids_32.find(thread_id_32) != thread_ids_32.end()) {
+        collision = true;
+        break;
+      }
+      thread_ids_32.insert(thread_id_32);
+      thread_id_map->insert(std::make_pair(thread_id_64, thread_id_32));
+    }
+  }
+
+  if (collision) {
+    // Since there was a collision, go back and assign each unique 64-bit thread
+    // ID its own sequential 32-bit equivalent. The 32-bit thread IDs will not
+    // bear any resemblance to the original 64-bit thread IDs.
+    thread_id_map->clear();
+    for (const ThreadSnapshot* thread_snapshot : thread_snapshots) {
+      uint64_t thread_id_64 = thread_snapshot->ThreadID();
+      if (thread_id_map->find(thread_id_64) == thread_id_map->end()) {
+        uint32_t thread_id_32 = thread_id_map->size();
+        thread_id_map->insert(std::make_pair(thread_id_64, thread_id_32));
+      }
+    }
+
+    DCHECK_LE(thread_id_map->size(), std::numeric_limits<uint32_t>::max());
+  }
+}
+
+}  // namespace crashpad