FastMM 4.92 FAQ
Frequently Asked Questions
常见问题：
--------------------------
Q: When my program shuts down FastMM reports that it has leaked memory. Is it possible that FastMM is wrong?
问：当我的程序关闭时，FastMM报告程序有内存泄漏。这有没有可能是FastMM出错了。
A: Unfortunately, no. If FastMM reports that a block has been leaked, then it means that a block was allocated but never freed - thus leaked. You may use FullDebugMode to shed more light on the cause of the problem.
Q: When I enable the FullDebugMode option my application crashes during startup. What's wrong?
问：当我启用FullDebugMode选项，程序在启动时就崩溃了。哪里出问题了？
A: The FastMM_FullDebugMode.dll library is required for FullDebugMode. Please make sure it is either in the same folder as the application, or it is accessible on the path.
Q: When a memory error pops up in "FullDebugMode" there is no debug info in the stack traces, only addresses. Why?
问：
A: For the FastMM_FullDebugMode.dll library to determine unit/line number information for stack traces any one of the following has to be available: TD32 debug info, a .map file, a .jdbg file or embedded JCL debug info. If none of these are available you will only get addresses in stack traces. For line numbers to be shown you also need to enable "Debug Information", "Reference Info" and "Use Debug DCUs". Also, if the addresses are inside a dynamically loaded DLL that was unloaded before shutdown then FastMM will not be able to determine unit/line number info for them.
Q: I have enable FullDebugMode and get a log file containing stack traces of memory leaks, but no line numbers. Why?
A: To get line numbers you also need to enable "Debug Information", "Reference Info" and "Use Debug DCUs" on the "Compiler" tab of the "Project Options" dialog.
Q: My program used to work fine with the Borland memory manager, but I get an "Invalid Pointer Operation" or "Access Violation" with FastMM. Is there a bug in FastMM?
A: Highly unlikely. The memory manager is such a critical part of any program and is subjected to such a large amount of traffic that it is rare that a bug of this nature will make it through testing. FastMM works differently than the default memory manager and does more pointer checking, so it will catch more errors. For example: The default MM may allow you to free the same pointer twice while FastMM will immediately raise an "Invalid Pointer Operation" if you try to do so. Compile your application with the "FullDebugMode" option set in FastMM4.pas - this should raise an error closer to the source of the problem.
Q: My program used to work with replacement memory manager X, but I get an access violation when I try to use FastMM. Why?
A: There may still be a reference to the old memory manager somewhere in the source. Do a "find in files" and check that the old memory manager is not referenced in any "uses" clause. FastMM checks that it is the first memory manager that is being installed, but many other memory managers don't, so it's quite possible that another MM may be installing itself after FastMM.
Q: FastMM doesn't make my program any faster. What's wrong?
A: If your program does not spend much time allocating and freeing memory, then there is little that FastMM can do to speed it up. For example: If your application spends only 1% of its time allocating memory using the default memory manager, a blazingly fast memory manager can at best make it 1% faster. FastMM is much faster than the default memory manager of Delphi 2005 (and older Delphi versions), but if the bottleneck in your program is not memory management then your gains may not be as great as you had hoped.
Q: I have added FastMM4.pas as the very first unit in my project's .dpr file, but when I try to run my program it still complains that it is not the first unit. Why?
A: If you are using an exception handler that modifies the unit initialization order (like MadExcept or EurekaLog), you have to change its configuration so that FastMM is initialized first.
Q: Delphi 2005 crashes with an error message "Class 'TApplication', already if class map" (sic) when I replace the default borlndmm.dll with the FastMM DLL. Why?
A: It is due to a bug in Delphi 2005 (QC#14007). There is an unofficial patch available that fixes this. Refer to FastMM4_Readme.txt for details.
Q: I am using the replacement borlndmm.dll together with the Delphi IDE. When I open up two copies of Delphi and then close one down I get a memory leak report. Why?
A: When compiling the DLL you should set the "NeverUninstall" option.
Q: I am using the replacement borlndmm.dll together with the Delphi 2005 IDE. When I close the IDE it remains in task manager. Why?
A: This is due to a bug (QC#14070). When compiling the DLL you should set the "NeverUninstall" option to work around it.
Q: My program used to work fine, but if I enable "FullDebugMode" and run it I get an access violation at address $8080xxxx. Why?
A: You are attempting to access properties of a freed object. When you free a block in "FullDebugMode", FastMM fills the freed memory area with a pattern of $80 bytes. If there were any pointers, long strings or object references inside the freed object they will now point to $80808080 which is in a reserved address space.
Q: In "FullDebugMode" when an error occurs the stack traces are very incomplete. Why?
A: You have probably disabled the "RawStackTraces" option. Without that option set, FastMM can only do a stack trace for routines that set up a stack frame. In the "Project Options" window on the "Compiler" tab, enable the "Stack Frames" option to create stack frames for all procedures. Note that the "RawStackTraces" option usually results in more complete stack traces, but may also introduce more (unavoidable) "false alarm" entries in the stack traces.
Q: How do I get my DLL and main application to share FastMM so I can safely pass long strings and dynamic arrays between them?
A: The easiest way is to define ShareMM, ShareMMIfLibrary and AttemptToUseSharedMM in FastMM4.pas and add FastMM4.pas to the top of the uses section of the .dpr for both the main application and the DLL.
Q: I am using Windows x64 edition. How do I enable my applications to address more than 2GB RAM?
A: Add a line containing {$SetPEFlags $20} to the .dpr file. This will set the LARGE_ADDRESS_AWARE flag in the executable and Windows x64 will consequently give the process a full 4GB user address space instead of the usual 2GB.
Q: I get the following error when I try to use FastMM with an application compiled to use packages: "[Error] Need imported data reference ($G) to access 'IsMultiThread' from unit 'FastMM4'". How do I get it to work?
A: Enable the "UseRuntimePackages" option in FastMM4Options.inc.
Q: I use runtime packages, and when my application shuts down I get a huge memory leak report followed by lots of access violations. Why?
A: This is most likely a package unload order problem: FastMM is uninstalled (and does the leak check) before all live pointers have been freed, and when the application subsequently tries to free the remaining live pointers the A/Vs occur. Either ensure that FastMM is unloaded last (using sharemem together with the replacement borlndmm.dll is one way), or use the "NeverUninstall" option and disable the memory leak report.
Q: Since version 4.29 "FullDebugMode" is really slow. Why?
A: It is because of the new "RawStackTraces" option. Switch it off and performance will be on par with previous versions, but stack traces will be less complete.
Q: I notice there is a precompiled debug borlndmm.dll for the IDE. Why would I need that?
A: You most likely won't. It's for hunting bugs in the IDE.
Q: If I replace the borlndmm.dll used by the IDE, how does this affect the memory manager used by my applications?
A: It doesn't. If your application has sharemem.pas as the first unit in the project's .dpr file then it will use the first borlndmm.dll it finds on the path. It does not have to be the same one that the IDE uses.
Q: Does enabling memory leak checking make my application slower?
A: No. Leak checking is only performed when the application shuts down.
Q: With both the FullDebugMode and RawStackTraces options enabled I sometimes get stack traces with entries in them that cannot possibly be correct. Why?
A: This is an unfortunate side-effect of doing a raw stack trace. While raw stack traces are usually more complete than the alternate frame-based tracing (used when the RawStackTraces option is disabled), it does sometimes raise false alarms when data entries on the stack happen to correspond to valid return addresses in program code. While the raw stack trace code does extensive tests to differentiate between data and return addresses, it does get it wrong sometimes and these incorrect entries are the result.
Q: I am trying to use FastMM inside a Kylix library, but I get a segmentation fault. Why?
A: Linux requires the code inside libraries to be position independent (with the base address indicated by ebx). The assembler code inside FastMM uses the ebx register for other purposes and is thus not position independent. If you want to use FastMM inside a Kylix library you have to disable the "ASMVersion" option in FastMM4Options.inc.
Q: How can I share the memory manager between BDS2006 applications that don't use FastMM and libraries that use FastMM (or vice versa)?
A: Add the SimpleShareMem.pas file as the first unit in the uses section of projects that use the default Delphi 2006 MM, and make sure that the sharing mechanism of FastMM ("ShareMM" and "AttemptToUseSharedMM" options) is enabled for projects that use FastMM, but also enable the "EnableSharingWithDefaultMM" option.
常见问题：
--------------------------
Q: When my program shuts down FastMM reports that it has leaked memory. Is it possible that FastMM is wrong?
问：当我的程序关闭时，FastMM报告程序有内存泄漏。这有没有可能是FastMM出错了。
A: Unfortunately, no. If FastMM reports that a block has been leaked, then it means that a block was allocated but never freed - thus leaked. You may use FullDebugMode to shed more light on the cause of the problem.
Q: When I enable the FullDebugMode option my application crashes during startup. What's wrong?
问：当我启用FullDebugMode选项，程序在启动时就崩溃了。哪里出问题了？
A: The FastMM_FullDebugMode.dll library is required for FullDebugMode. Please make sure it is either in the same folder as the application, or it is accessible on the path.
Q: When a memory error pops up in "FullDebugMode" there is no debug info in the stack traces, only addresses. Why?
问：
A: For the FastMM_FullDebugMode.dll library to determine unit/line number information for stack traces any one of the following has to be available: TD32 debug info, a .map file, a .jdbg file or embedded JCL debug info. If none of these are available you will only get addresses in stack traces. For line numbers to be shown you also need to enable "Debug Information", "Reference Info" and "Use Debug DCUs". Also, if the addresses are inside a dynamically loaded DLL that was unloaded before shutdown then FastMM will not be able to determine unit/line number info for them.
Q: I have enable FullDebugMode and get a log file containing stack traces of memory leaks, but no line numbers. Why?
A: To get line numbers you also need to enable "Debug Information", "Reference Info" and "Use Debug DCUs" on the "Compiler" tab of the "Project Options" dialog.
Q: My program used to work fine with the Borland memory manager, but I get an "Invalid Pointer Operation" or "Access Violation" with FastMM. Is there a bug in FastMM?
A: Highly unlikely. The memory manager is such a critical part of any program and is subjected to such a large amount of traffic that it is rare that a bug of this nature will make it through testing. FastMM works differently than the default memory manager and does more pointer checking, so it will catch more errors. For example: The default MM may allow you to free the same pointer twice while FastMM will immediately raise an "Invalid Pointer Operation" if you try to do so. Compile your application with the "FullDebugMode" option set in FastMM4.pas - this should raise an error closer to the source of the problem.
Q: My program used to work with replacement memory manager X, but I get an access violation when I try to use FastMM. Why?
A: There may still be a reference to the old memory manager somewhere in the source. Do a "find in files" and check that the old memory manager is not referenced in any "uses" clause. FastMM checks that it is the first memory manager that is being installed, but many other memory managers don't, so it's quite possible that another MM may be installing itself after FastMM.
Q: FastMM doesn't make my program any faster. What's wrong?
A: If your program does not spend much time allocating and freeing memory, then there is little that FastMM can do to speed it up. For example: If your application spends only 1% of its time allocating memory using the default memory manager, a blazingly fast memory manager can at best make it 1% faster. FastMM is much faster than the default memory manager of Delphi 2005 (and older Delphi versions), but if the bottleneck in your program is not memory management then your gains may not be as great as you had hoped.
Q: I have added FastMM4.pas as the very first unit in my project's .dpr file, but when I try to run my program it still complains that it is not the first unit. Why?
A: If you are using an exception handler that modifies the unit initialization order (like MadExcept or EurekaLog), you have to change its configuration so that FastMM is initialized first.
Q: Delphi 2005 crashes with an error message "Class 'TApplication', already if class map" (sic) when I replace the default borlndmm.dll with the FastMM DLL. Why?
A: It is due to a bug in Delphi 2005 (QC#14007). There is an unofficial patch available that fixes this. Refer to FastMM4_Readme.txt for details.
Q: I am using the replacement borlndmm.dll together with the Delphi IDE. When I open up two copies of Delphi and then close one down I get a memory leak report. Why?
A: When compiling the DLL you should set the "NeverUninstall" option.
Q: I am using the replacement borlndmm.dll together with the Delphi 2005 IDE. When I close the IDE it remains in task manager. Why?
A: This is due to a bug (QC#14070). When compiling the DLL you should set the "NeverUninstall" option to work around it.
Q: My program used to work fine, but if I enable "FullDebugMode" and run it I get an access violation at address $8080xxxx. Why?
A: You are attempting to access properties of a freed object. When you free a block in "FullDebugMode", FastMM fills the freed memory area with a pattern of $80 bytes. If there were any pointers, long strings or object references inside the freed object they will now point to $80808080 which is in a reserved address space.
Q: In "FullDebugMode" when an error occurs the stack traces are very incomplete. Why?
A: You have probably disabled the "RawStackTraces" option. Without that option set, FastMM can only do a stack trace for routines that set up a stack frame. In the "Project Options" window on the "Compiler" tab, enable the "Stack Frames" option to create stack frames for all procedures. Note that the "RawStackTraces" option usually results in more complete stack traces, but may also introduce more (unavoidable) "false alarm" entries in the stack traces.
Q: How do I get my DLL and main application to share FastMM so I can safely pass long strings and dynamic arrays between them?
A: The easiest way is to define ShareMM, ShareMMIfLibrary and AttemptToUseSharedMM in FastMM4.pas and add FastMM4.pas to the top of the uses section of the .dpr for both the main application and the DLL.
Q: I am using Windows x64 edition. How do I enable my applications to address more than 2GB RAM?
A: Add a line containing {$SetPEFlags $20} to the .dpr file. This will set the LARGE_ADDRESS_AWARE flag in the executable and Windows x64 will consequently give the process a full 4GB user address space instead of the usual 2GB.
Q: I get the following error when I try to use FastMM with an application compiled to use packages: "[Error] Need imported data reference ($G) to access 'IsMultiThread' from unit 'FastMM4'". How do I get it to work?
A: Enable the "UseRuntimePackages" option in FastMM4Options.inc.
Q: I use runtime packages, and when my application shuts down I get a huge memory leak report followed by lots of access violations. Why?
A: This is most likely a package unload order problem: FastMM is uninstalled (and does the leak check) before all live pointers have been freed, and when the application subsequently tries to free the remaining live pointers the A/Vs occur. Either ensure that FastMM is unloaded last (using sharemem together with the replacement borlndmm.dll is one way), or use the "NeverUninstall" option and disable the memory leak report.
Q: Since version 4.29 "FullDebugMode" is really slow. Why?
A: It is because of the new "RawStackTraces" option. Switch it off and performance will be on par with previous versions, but stack traces will be less complete.
Q: I notice there is a precompiled debug borlndmm.dll for the IDE. Why would I need that?
A: You most likely won't. It's for hunting bugs in the IDE.
Q: If I replace the borlndmm.dll used by the IDE, how does this affect the memory manager used by my applications?
A: It doesn't. If your application has sharemem.pas as the first unit in the project's .dpr file then it will use the first borlndmm.dll it finds on the path. It does not have to be the same one that the IDE uses.
Q: Does enabling memory leak checking make my application slower?
A: No. Leak checking is only performed when the application shuts down.
Q: With both the FullDebugMode and RawStackTraces options enabled I sometimes get stack traces with entries in them that cannot possibly be correct. Why?
A: This is an unfortunate side-effect of doing a raw stack trace. While raw stack traces are usually more complete than the alternate frame-based tracing (used when the RawStackTraces option is disabled), it does sometimes raise false alarms when data entries on the stack happen to correspond to valid return addresses in program code. While the raw stack trace code does extensive tests to differentiate between data and return addresses, it does get it wrong sometimes and these incorrect entries are the result.
Q: I am trying to use FastMM inside a Kylix library, but I get a segmentation fault. Why?
A: Linux requires the code inside libraries to be position independent (with the base address indicated by ebx). The assembler code inside FastMM uses the ebx register for other purposes and is thus not position independent. If you want to use FastMM inside a Kylix library you have to disable the "ASMVersion" option in FastMM4Options.inc.
Q: How can I share the memory manager between BDS2006 applications that don't use FastMM and libraries that use FastMM (or vice versa)?
A: Add the SimpleShareMem.pas file as the first unit in the uses section of projects that use the default Delphi 2006 MM, and make sure that the sharing mechanism of FastMM ("ShareMM" and "AttemptToUseSharedMM" options) is enabled for projects that use FastMM, but also enable the "EnableSharingWithDefaultMM" option.