diff --git a/documentation/server/guides/memory-leaks-and-usage.md b/documentation/server/guides/memory-leaks-and-usage.md index c340bd8a8..c79b9dded 100644 --- a/documentation/server/guides/memory-leaks-and-usage.md +++ b/documentation/server/guides/memory-leaks-and-usage.md @@ -4,47 +4,107 @@ layout: page title: Debugging Memory Leaks and Usage --- -There are many different tools for troubleshooting memory leaks both on Linux and macOS, each with different strengths and ease-of-use. One excellent tool is the Xcode's [Memory Graph Debugger](https://developer.apple.com/library/archive/documentation/DeveloperTools/Conceptual/debugging_with_xcode/chapters/special_debugging_workflows.html#//apple_ref/doc/uid/TP40015022-CH9-DontLinkElementID_1). -[Instruments](https://help.apple.com/instruments/mac/10.0/#/dev022f987b) and `leaks` can also be very useful. If you cannot run or reproduce the problem on macOS, there are a number of server-side alternatives below. +Debugging memory leaks and usage helps you identify and resolve issues related to memory management in an application. -## Example program +Memory leaks occur when memory is allocated but not properly deallocated, leading to a gradual increase in memory usage over time. This can severely impact an application's performance and stability. -The following program doesn't do anything useful but leaks memory so will serve as the example: +It’s important to note, however, that a gradual increase in memory usage over time doesn’t always indicate a leak. Instead, it may be the memory profile of the application. For example, when an application’s cache gradually fills over time it shows the same gradual increase in memory. Accordingly, configuring the cache so it doesn’t expand beyond a designated limit will cause the memory usage to plateau. Additionally, allocator libraries don't always immediately return memory feedback to the system due to performance or other reasons. But it will stabilize over time. -```swift -public class MemoryLeaker { - var closure: () -> Void = { () } +Debugging memory leaks in Swift on macOS and Linux environments can be done using different tools and techniques, each with distinct strengths and usability. - public init() {} +Basic troubleshooting steps include: - public func doNothing() {} +1. Using profiling tools, provided by the respective operating systems and development environments, to identify and analyze memory usage. - public func doSomethingThatLeaks() { - self.closure = { - // This will leak as it'll create a permanent reference cycle: - // - // self -> self.closure -> self - self.doNothing() - } - } -} + **For macOS**, [Memory Graph Debugger](https://developer.apple.com/documentation/xcode/gathering-information-about-memory-use#Inspect-the-debug-memory-graph) and this [Detect and diagnose memory issues](https://developer.apple.com/videos/play/wwdc2021/10180/) video are helpful. You can also use the [Xcode Instruments](https://help.apple.com/instruments/mac/10.0/#/dev022f987b) tool for various profiling instruments including the [Allocations instrument](https://developer.apple.com/documentation/xcode/gathering-information-about-memory-use#Profile-your-app-using-the-Allocations-instrument) to track memory allocation and deallocation in your Swift code. + + **For Linux**, you can use tools like [Valgrind](https://valgrind.org/) or [Heaptrack](https://github.com/KDE/heaptrack) to profile your application as shown in the examples below. Although these tools are primarily used for C/C++ code, they can also work with Swift. + +2. Reviewing code and identifying potential leaks to examine your code for any potential areas where memory leaks may occur. Common sources of leaks include retained references or unbalanced retain-release cycles, which rarely apply to Swift since it performs [automatic reference counting (ARC)](https://docs.swift.org/swift-book/documentation/the-swift-programming-language/automaticreferencecounting/). + +> Note: Memory leaks can occur in Swift if there are substantial reference cycles between objects that involve closures or if objects hold references to external resources that are not released properly. However, the likelihood of such issues is significantly reduced through the automatic memory management's ability to add and remove references, making sources of leaks like retained references and unbalanced retain-release cycles less common in Swift code. + +3. Enabling debug memory allocation features allows you to get additional information about objects and their memory allocations. + + **On macOS**, you can enable Zombie Objects using Xcode or use [MallocStackLogging](https://developer.apple.com/videos/play/wwdc2022/10106/) to detect over-released or accessed deallocated objects. + + To enable Zombie Objects: + 1. Open your Xcode project. + 2. Go to the **Edit Scheme** menu by clicking on the scheme dropdown in the toolbar. + 3. In the scheme editor window, select the **Run** tab. + 4. Choose the **Diagnostics** tab. + 5. Under **Memory Management**, check the box next to **Enable Zombie Objects**. + + **On Linux**, Swift has built-in LeakSanitizer support that can be enabled using the `-sanitize=leak` compiler flag. + +### Troubleshooting + +This section aims to provide you with helpful server-side troubleshooting techniques to debug leaks and usage using **Valgrind**, **LeakSanitizer**, and **Heaptrack**. +The following **example program** leaks memory. We are using it as an *example only* to illustrate the various troubleshooting methods mentioned below. +``` +public class MemoryLeaker { + var closure: () -> Void = { () } + + public init() {} + + public func doNothing() {} + + public func doSomethingThatLeaks() { + self.closure = { + // This will leak as it'll create a permanent reference cycle: + // + // self -> self.closure -> self + self.doNothing() + } + } +} @inline(never) // just to be sure to get this in a stack trace func myFunctionDoingTheAllocation() { - let thing = MemoryLeaker() - thing.doSomethingThatLeaks() + let thing = MemoryLeaker() + thing.doSomethingThatLeaks() } myFunctionDoingTheAllocation() ``` +## Debugging leaks with Valgrind +Valgrind is an open-source framework for debugging and profiling Linux applications. It provides several tools, including Memcheck, which can detect memory leaks, invalid memory accesses, and other memory errors. Although Valgrind is primarily focused on C/C++ applications, it can also be used with Swift on Linux. -## Debugging leaks with `valgrind` +To debug memory leaks using Valgrind, install it on your system. -If you run your program using +**For MacOS**: +1. Open a Terminal session. +2. [Install Homebrew](https://brew.sh/) if you haven't already. +3. Once `Homebrew` is installed, run this command to install `valgrind`: - valgrind --leak-check=full ./test +```bash +brew install valgrind +``` -then `valgrind` will output +4. Enter your password if prompted to authorize the software installation and allow Homebrew to complete the installation process. Confirm the installation when requested. + +Valgrind should be successfully installed on your system using the system package manager. + +5. Once you've compiled your program (in this case, a binary named `test`), run the following `valgrind` command to enable full leak checking: +``` +valgrind --leak-check=full ./test +``` + +**For Swift on Linux**: + +1. Install Swift on your Linux system. You can download and install Swift from the [official website](https://swift.org/download/). + +2. Install Valgrind on your Linux system by using your package manager. For example, if you are using Ubuntu, you can run the following command: +``` +sudo apt-get install valgrind +``` + +3. Once Valgrind is installed, run the following command: +``` +valgrind --leak-check=full swift run +``` + +The `valgrind` command analyzes the program for any memory leaks and shows the relevant information about the leak, including the stack trace where the allocation occurred as shown below: ``` ==1== Memcheck, a memory error detector @@ -78,8 +138,7 @@ then `valgrind` will output ==1== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0) ``` -The important part is - +The following trace block (from above) indicates a memory leak. ``` ==1== 32 bytes in 1 blocks are definitely lost in loss record 1 of 4 ==1== at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) @@ -90,8 +149,20 @@ The important part is ==1== by 0x108CA3: main (in /tmp/test) ``` -which can demangled by pasting it into `swift demangle`: +However, since Swift uses name mangling for function and symbol names, the stack traces may not be straightforward to understand. +To demangle the Swift symbols in the stack traces, run the `swift demangle` command: +``` +swift demangle +``` + +Replace `` with the mangled symbol name shown in the stack trace. For example: + +`swift demangle $s4test12MemoryLeakerCACycfC` + +> Note: `swift demangle` is a Swift command line utility and should be available if you have the Swift toolchain installed. + +The utility will demangle the symbol and display a human-readable version as follows: ``` ==1== 32 bytes in 1 blocks are definitely lost in loss record 1 of 4 ==1== at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) @@ -102,23 +173,33 @@ which can demangled by pasting it into `swift demangle`: ==1== by 0x108CA3: main (in /tmp/test) ``` -So valgrind is telling us that the allocation that eventually leaked is coming from `test.myFunctionDoingTheAllocation` calling `test.MemoryLeaker.__allocating_init()` which is correct. +By analyzing the demangled symbols, we can understand which part of the code is responsible for the memory leak. In this example, the `valgrind` command indicates the allocation that leaked is coming from: -### Limitations +`test.myFunctionDoingTheAllocation` calling `test.MemoryLeaker.__allocating_init()` -- `valgrind` doesn't understand the bit packing that is used in many Swift data types (like `String`) or when you create `enum`s with associated values. Therefore `valgrind` sometimes claims a certain allocation was leaked even though it might not have -- `valgrind` will make your program run _very slow_ (possibly 100x slower) which might stop you from even getting far enough to reproduce the issue. +### Limitations -## Debugging leaks with `Leak Sanitizer` +* The `valgrind` command doesn’t understand the bit-packing used in many Swift data types like `String` or when `enums` are created with associated values. Consequently, using the `valgrind` command sometimes reports memory errors or leaks that do not exist, and false negatives occur when it fails to detect actual issues. +* The `valgrind` command makes your program run exceptionally slow (possibly 100x slower), which may hinder your ability to reproduce the problem and analyze the performance. +* Valgrind is primarily supported on Linux. Its support for other platforms, such as macOS or iOS, may be limited or nonexistent. -If you build your application using +## Debugging leaks with LeakSanitizer +LeakSanitizer is a memory leak detector that is integrated into [AddressSanitizer](https://developer.apple.com/documentation/xcode/diagnosing-memory-thread-and-crash-issues-early). To debug memory leaks using LeakSanitizer with Address Sanitizer enabled on Swift, you will need to set the appropriate environment variable, compile your Swift package with the necessary options, and then run your application. - swift build --sanitize=address +Here are the steps: -it will be built with [Address Sanitizer](https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer) enabled. Address Sanitizer also automatically tries to find leaked memory blocks, just like `valgrind`. +1. Open a terminal session and navigate to your Swift package directory. +2. Set the `ASAN_OPTIONS` environment variable to enable AddressSanitizer and configure its behavior. You can do this by running the command: +``` +export ASAN_OPTIONS=detect_leaks=1 +``` -The output from the above example program would be +3. Run `swift build` with the additional option to enable [Address Sanitizer](https://developer.apple.com/documentation/xcode/diagnosing-memory-thread-and-crash-issues-early): +``` +swift build --sanitize=address +``` +The build process will compile your code with AddressSanitizer enabled, which automatically looks for leaked memory blocks. If any memory leaks during the build are detected, it will output the information (similar to Valgrind) as shown in the example below: ``` ================================================================= ==478==ERROR: LeakSanitizer: detected memory leaks @@ -132,30 +213,54 @@ Direct leak of 32 byte(s) in 1 object(s) allocated from: SUMMARY: AddressSanitizer: 32 byte(s) leaked in 1 allocation(s). ``` +Currently, the output doesn’t provide a human-readable representation of the function names because [LeakSanitizer doesn't symbolicate stack traces on Linux](https://github.com/apple/swift/issues/55046). + +However, you can symbolicate it using `llvm-symbolizer` or `addr2line` if you have `binutils` installed. + +To install `binutils` for Swift on a server running Linux, follow these steps: +1. Connect to your Swift server through SSH using a terminal. +2. Update the package lists by running the following command: +``` +sudo apt update +``` -which shows the same information as `valgrind`, unfortunately however not symbolicated due to [SR-12601](https://bugs.swift.org/browse/SR-12601). +3. Install `binutils` by running the following command: +``` +sudo apt install binutils +``` -You can symbolicate it using `llvm-symbolizer` or `addr2line` if you have `binutils` installed like so: +4. This will install `binutils` and its related tools for working with binaries, object files, and libraries, which can be useful for developing and debugging Swift applications on Linux. +You can now run the following command to demangle the symbols in the stack traces: ``` # /tmp/test+0xc62ce -addr2line -e /tmp/test -a 0xc62ce -ipf | swift demangle +addr2line -e /tmp/test -a 0xc62ce -ipf | swift demangle +``` + +In this example, the allocation that leaked is coming from: +``` 0x00000000000c62ce: test.myFunctionDoingTheAllocation() -> () at crtstuff.c:? ``` -## Debugging transient memory usage with `heaptrack` -[Heaptrack](https://github.com/KDE/heaptrack) is very useful for analyzing memory leaks/usage with less overhead than `valgrind` - but more importantly is also allows for analyzing transient memory usage which may significantly impact performance by putting to much pressure on the allocator. -In addition to command line access, there is a graphical front-end `heaptrack_gui`. +### Limitations + +* LeakSanitizer may not be as effective in detecting and reporting all types of memory leaks in Swift code compared to languages like C or C++. +* False positives occur when LeakSanitizer reports a memory leak that does not exist. +* LeakSanitizer is primarily supported on macOS and Linux. While it is possible to use LeakSanitizer on iOS or other platforms that support Swift, there may be limitations or platform-specific issues that need to be considered. +* Enabling Address Sanitizer and LeakSanitizer in your Swift project can have a performance impact. It is recommended to use LeakSanitizer for targeted analysis and debugging rather than continuously running it in production environments. -A key feature is that it allows for diffing between two different runs of your application, making it fairly easy to troubleshoot differences in `malloc` behavior between e.g. feature branches and main. +## Debugging transient memory usage with Heaptrack +[Heaptrack](https://github.com/KDE/heaptrack) is an open-source heap memory profiler tool that helps find and analyze memory leaks and usage with less overhead than Valgrind. It also allows for analyzing and debugging transient memory usage in your application. However, it may significantly impact performance by overloading the allocator. -A short how-to run on Ubuntu 20.04 (using a different example than above, as we look at transient usage in this example), install `heaptrack` with: +A GUI front-end analyzer `heaptrack_gui` is available in addition to command line access. The analyzer allows for diffing between two different runs of your application to troubleshoot variations in `malloc` behavior between the `feature branch` and `main`. +Using a different example, here’s a short how-to using [Ubuntu](https://www.swift.org/download/) to analyze transient usage. +1. Install `heaptrack` by running this command: ``` sudo apt-get install heaptrack ``` -Then run the binary with `heaptrack` two times — first we do it for `main` to get a baseline: +2. Run the binary twice using `heaptrack`. The first run provides a baseline for `main`. ``` > heaptrack .build/x86_64-unknown-linux-gnu/release/test_1000_autoReadGetAndSet heaptrack output will be written to "/tmp/.nio_alloc_counter_tests_GRusAy/heaptrack.test_1000_autoReadGetAndSet.84341.gz" @@ -169,7 +274,8 @@ Heaptrack finished! Now run the following to investigate the data: heaptrack --analyze "/tmp/.nio_alloc_counter_tests_GRusAy/heaptrack.test_1000_autoReadGetAndSet.84341.gz" ``` -Then run it a second time for the feature branch: + +3. Then run it a second time for the `feature branch` by changing the branch and recompiling. ``` > heaptrack .build/x86_64-unknown-linux-gnu/release/test_1000_autoReadGetAndSet heaptrack output will be written to "/tmp/.nio_alloc_counter_tests_GRusAy/heaptrack.test_1000_autoReadGetAndSet.84372.gz" @@ -184,17 +290,17 @@ Heaptrack finished! Now run the following to investigate the data: heaptrack --analyze "/tmp/.nio_alloc_counter_tests_GRusAy/heaptrack.test_1000_autoReadGetAndSet.84372.gz" ubuntu@ip-172-31-25-161 /t/.nio_alloc_counter_tests_GRusAy> ``` -Here we could see that we had 673989 allocations in the feature branch version and 319347 in `main`, so clearly a regression. -Finally, we can analyze the output as a diff from these runs using `heaptrack_print` and pipe it through `swift demangle` for readability: +The output shows 673989 allocations in the `feature branch` version and 319347 in `main`, indicating a regression. +4. Run the following command to analyze the output as a diff from these runs using `heaptrack_print` and pipe it through `swift demangle` for readability: ``` heaptrack_print -T -d heaptrack.test_1000_autoReadGetAndSet.84341.gz heaptrack.test_1000_autoReadGetAndSet.84372.gz | swift demangle ``` -`-T` gives us the temporary allocations (as it in this case was not a leak, but a transient allocation - if you have leaks remove `-T`). -The output can be quite long, but in this case as we look for transient allocations, scroll down to: +> Note: `-T` outputs the temporary allocations, providing transient allocations and not leaks. If leaks are detected, remove `-T`. +Scroll down to see the transient allocations (output may be long): ``` MOST TEMPORARY ALLOCATIONS 307740 temporary allocations of 290324 allocations in total (106.00%) from @@ -232,8 +338,7 @@ swift_slowAlloc 22196 temporary allocations of 22276 allocations in total (99.64%) from: ``` -And here we could fairly quickly see that the transient extra allocations was due to extra debug printing and querying of environment variables: - +Looking at the output above, we can see the extra transient allocations were due to extra debug printing and querying of environment variables as shown below: ``` NIO.URing.getEnvironmentVar(Swift.String) -> Swift.String? at /home/ubuntu/swiftnio/swift-nio/Sources/NIO/LinuxURing.swift:291 @@ -241,4 +346,11 @@ NIO.URing.getEnvironmentVar(Swift.String) -> Swift.String? NIO.URing._debugPrint(@autoclosure () -> Swift.String) -> () ``` -And this code will be removed before final integration of the feature branch, so the diff will go away. +In this example, the debug prints are only for testing and would be removed from the code before the branch is merged. + +> Tip: Heaptrack can also be [installed on an RPM-based distribution](https://rhel.pkgs.org/8/epel-x86_64/heaptrack-1.2.0-7.el8.x86_64.rpm.html) to debug transient memory usage. You may need to consult the distribution's documentation for the specific repository setup steps. When Heaptrack is installed correctly, it should display its version and usage information. + +### Limitations + +* It's important to note that Heaptrack was primarily designed for C and C++ applications, so its support for Swift applications is limited. +* While Heaptrack can provide insights into memory allocations and deallocations in a Swift application, it may not capture certain Swift-specific memory management mechanisms like Swift's built-in Instruments profiler.