Per isolate Log with block support

runtime/vm/log.h

Index: runtime/vm/log.h
diff --git a/runtime/vm/log.h b/runtime/vm/log.h
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+++ b/runtime/vm/log.h
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+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#ifndef VM_LOG_H_
+#define VM_LOG_H_
+
+#include "vm/allocation.h"
+#include "vm/growable_array.h"
+#include "vm/os.h"
+
+namespace dart {
+
+class Isolate;
+class LogBlock;
+class Thread;
+
+#if defined(_MSC_VER)
+#define ISL_Print(format, ...) \
+    Isolate::Current()->Log()->Print(format, __VA_ARGS__)
+#else
+#define ISL_Print(format, ...) \
+    Isolate::Current()->Log()->Print(format, ##__VA_ARGS__)
+#endif
+
+typedef void (*LogPrinter)(const char* str, ...);
+
+class Log {
+ public:
+  explicit Log(LogPrinter printer = OS::Print);
+
+  // Append a formatted string to the log.
+  void Print(const char* format, ...) PRINTF_ATTRIBUTE(2, 3);
+
+  // Flush and truncate the log. The log is flushed starting at cursor
+  // and truncated to cursor afterwards.
+  void Flush(const intptr_t cursor = 0);
+
+  // Clears the log.
+  void Clear();
+
+  // Current cursor.
+  intptr_t cursor() const;
+
+  // A logger that does nothing.
+  static Log* NoOpLog();
+
+ private:
+  void TerminateString();
+  void EnableManualFlush();
+  void DisableManualFlush();
+
+  static Log noop_log_;
+  LogPrinter printer_;
+  intptr_t manual_flush_;
+  MallocGrowableArray<char> buffer_;
+
+  friend class LogBlock;
+  friend class LogTestHelper;
+  DISALLOW_COPY_AND_ASSIGN(Log);
+};
+
+
+// Causes all log messages to be buffered until destructor is called.
+// Can be nested.
+class LogBlock : public StackResource {
+ public:
+  LogBlock(Isolate* isolate, Log* log)
+      : StackResource(isolate),
+        log_(log), cursor_(log->cursor()) {
+    CommonConstructor();
+  }
+
+  explicit LogBlock(Isolate* isolate);
+  explicit LogBlock(Thread* thread);
+
+  LogBlock(Thread* thread, Log* log);
+
+  ~LogBlock() {
+    CommonDestructor();
+  }
+
+ private:
+  void CommonConstructor() {
+    log_->EnableManualFlush();
+  }
+
+  void CommonDestructor() {
+    log_->Flush(cursor_);
+    log_->DisableManualFlush();
+  }
+  Log* log_;
+  const intptr_t cursor_;
+};
+
+}  // namespace dart
+
+#endif  // VM_LOG_H_