Make logging use a fixed-length buffer to avoid race conditions.

Previously, race conditions occurred inside logging, that caused
segfaults because a thread was trying to use an old pointer that
was freed when the string was reallocated. Using a fixed-length buffer
avoids this, at the cost of cutting too long messages over seveal lines.

diff --git a/src/log.cpp b/src/log.cpp
index 600e715c12680653379b935551aa2e48384bbffe..589cfd909806ee7ba6be55d720c6f06ba486a6bf 100644 (file)
--- a/src/log.cpp
+++ b/src/log.cpp
@@ -34,9 +34,13 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include <cerrno>
 #include <cstring>
 
+const int BUFFER_LENGTH = 256;
+
 class StringBuffer : public std::streambuf {
 public:
-       StringBuffer() {}
+       StringBuffer() {
+               buffer_index = 0;
+       }
 
        int overflow(int c);
        virtual void flush(const std::string &buf) = 0;
@@ -44,7 +48,8 @@ public:
        void push_back(char c);
 
 private:
-       std::string buffer;
+       char buffer[BUFFER_LENGTH];
+       int buffer_index;
 };
 
 
@@ -338,11 +343,18 @@ std::streamsize StringBuffer::xsputn(const char *s, std::streamsize n)
 void StringBuffer::push_back(char c)
 {
        if (c == '\n' || c == '\r') {
-               if (!buffer.empty())
-                       flush(buffer);
-               buffer.clear();
+               if (buffer_index)
+                       flush(std::string(buffer, buffer_index));
+               buffer_index = 0;
        } else {
-               buffer.push_back(c);
+               int index = buffer_index;
+               buffer[index++] = c;
+               if (index >= BUFFER_LENGTH) {
+                       flush(std::string(buffer, buffer_index));
+                       buffer_index = 0;
+               } else {
+                       buffer_index = index;
+               }
        }
 }