Re: std::map multithreaded access, lock needed?

James Kanze <>
Thu, 10 Jan 2008 01:47:12 -0800 (PST)
On Jan 10, 2:29 am, "Christopher Pisz" <> wrote:

With the recent acceptance of multithreading questions, I assume this
question is on topic. If not, let me know.

I have a singleton is going to be accessed by any threads. My singleton
class contains a static std::map that will be read and written to. I am
wondering if I need to lock it when being read from and written to? The sgi
docs lead me to beleive I do... See LoggerWindow::OpenLog below.

// in the .h

#include "LogWindow.h"

#include <map>


class LoggerWindow

* Constructor

* Destructor

* Creates child windows for one log
void OpenLog(std::string title);



static HANDLE m_frameCreated; // Event that is signalled when the frame
window has been created

/** Pointers to the LogWindow instances that are the MDI children */
typedef std::map<std::string, LogWindow *> LogWindows;
static LogWindows m_logWindows;



// in the .cpp

#include "LoggerWindow.h"


// Initialize static members of the LoggerWindow class


HANDLE LoggerWindow::m_frameCreated = CreateEvent(NULL, TRUE, FALSE, NULL);
LoggerWindow::LogWindows LoggerWindow::m_logWindows;



void LoggerWindow::OpenLog(std::string title)
   // This operation cannot execute until the frame window is fully created
   WaitForSingleObject(m_frameCreated, INFINITE);

   // Is a lock needed here????

   // Check if the LogWindow already exists
   LogWindows::iterator it = m_logWindows.find(title);
   if( it == m_logWindows.end() )
      // Create a Log Window which is an MDI child of this window
      LogWindow * logWindow = new LogWindow(m_hwndClient, title);
      m_logWindows[title] = logWindow;

   // Is an unlock needed here????



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