make glogstyleformatter stop guessing

Summary: Might as well store the count of newlines in the Log Message - as the field is already padded to <pointersize> bytes by the alignment requirements of the field either side it will not use any more space than the existing `bool`

Reviewed By: simpkins

Differential Revision: D20200298

fbshipit-source-id: 84cc52898069eae1af5bd0f103d4ab3177c45206

folly/logging/GlogStyleFormatter.cpp

@@ -96,12 +96,8 @@ std::string GlogStyleFormatter::formatMessage(
     header.reserve(headerLengthGuess);
     headerFormatter.appendTo(header);
 
-    // Make a guess at how many lines will be in the message, just to make an
-    // initial buffer allocation.  If the guess is too small then the string
-    // will reallocate and grow as necessary, it will just be slightly less
-    // efficient than if we had guessed enough space.
-    size_t numLinesGuess = 4;
-    buffer.reserve(((header.size() + 1) * numLinesGuess) + msgData.size());
+    buffer.reserve(
+        ((header.size() + 1) * message.getNumNewlines()) + msgData.size());
 
     size_t idx = 0;
     while (true) {

folly/logging/LogMessage.cpp

@@ -84,6 +84,7 @@ StringPiece LogMessage::getFileBaseName() const {
 void LogMessage::sanitizeMessage() {
   // Compute how long the sanitized string will be.
   size_t sanitizedLength = 0;
+  size_t numNewlines = 0;
   for (const char c : rawMessage_) {
     if (c == '\\') {
       // Backslashes are escaped as two backslashes
@@ -93,7 +94,7 @@ void LogMessage::sanitizeMessage() {
       // All other control characters are emitted as \xNN (4 characters)
       if (c == '\n') {
         sanitizedLength += 1;
-        containsNewlines_ = true;
+        ++numNewlines;
       } else if (c == '\t') {
         sanitizedLength += 1;
       } else {
@@ -107,7 +108,7 @@ void LogMessage::sanitizeMessage() {
       ++sanitizedLength;
     }
   }
-
+  numNewlines_ = numNewlines;
   // If nothing is different, just use rawMessage_ directly,
   // and don't populate message_.
   if (sanitizedLength == rawMessage_.size()) {

folly/logging/LogMessage.h

@@ -116,7 +116,11 @@ class LogMessage {
   }
 
   bool containsNewlines() const {
-    return containsNewlines_;
+    return numNewlines_ > 0;
+  }
+
+  size_t getNumNewlines() const {
+    return numNewlines_;
   }
 
  private:
@@ -143,12 +147,13 @@ class LogMessage {
   folly::StringPiece const functionName_;
 
   /**
-   * containsNewlines_ will be true if the message contains internal newlines.
+   * containedNewlines_ counts the number of internal newlines in the message.
    *
    * This allows log handlers that perform special handling of multi-line
-   * messages to easily detect if a message contains multiple lines or not.
+   * messages to easily detect if a message contains multiple lines or not and
+   * size their buffers appropriately.
    */
-  bool containsNewlines_{false};
+  size_t numNewlines_{0};
 
   /**
    * rawMessage_ contains the original message.