heap(1) General Commands Manual heap(1)

heap — List all the malloc-allocated buffers in the process's heap

heap [-s | -sortBySize] [-z | -zones] [-guessNonObjects] [-sumObjectFields] [-showSizes] [-addresses all | <classes-pattern>] [-noContent] pid | partial-executable-name | memory-graph-file

heap lists the objects currently allocated on the heap of the specified process, as well as summary data. Objects are categorized by class name, type (Objective-C, C++, or CFType), and binary image. C++ objects are identified by the vtable referenced from the start of the object, so with multiple inheritance this may not give the precise class of the object.

If the target process is running with MallocStackLogging, then heap attempts to identify the types of "non-object" allocations, using the form "<allocation-call> in <caller>". The <caller> is determined by walking up the allocation stack backtrace (if available) to find the symbol name of the function that called an "allocation function", such as malloc, calloc, realloc, C++ "operator new", strndup, various internal functions of libc++.1.dylib, etc. If <caller> is a C++ function, the type name is created by simplifying the demangled symbol name by removing the return type, the "__1::" substrings from use of llvm's libc++abi.dylib, and standard arguments such as "std::__1::allocator<T>"."

For example, this type information:

malloc in std::basic_string<char>::basic_string<std::nullptr_t>(char const*)  C++     Metal

is determined from the backtrace:

_malloc_zone_malloc (in libsystem_malloc.dylib)
 
operator new(unsigned long) (in libc++abi.dylib)
 
std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::basic_string<std::nullptr_t>(char const*) (in Metal)
 
...
 

The binary image identified for a class is the image which implements the class. For types derived from allocation backtraces, the binary image is that of <caller>.

heap requires one argument -- either the process ID or the full or partial executable name of the process to examine, or the pathname of a memory graph file generated by leaks or the Xcode Memory Graph Debugger.

The following options are available:

|
Sort output by total size of class instances, rather than by count.
|
Show the output separated out into the different malloc zones, instead of an aggregated summary of all zones.
|
"Human-readable" output. Use unit suffixes: K, M, G, and T in order to reduce the number of digits to three or less using base 2 for sizes.
Look through the memory contents of each Objective-C object to find pointers to malloc'ed blocks (non-objects), such as the variable array hanging from an NSArray. These referenced blocks of memory are identified as their offset from the start of the object (say "__NSCFArray[12]"). The count, number of bytes, and average size of memory blocks referenced from each different object offset location are listed in the output.
Do the same analysis as with the -guessNonObjects option, but add the sizes of those referenced non-object fields into the entries for the corresponding objects.
Show the distribution of each malloc size for each object, instead of summing and averaging the sizes in a single entry.
Show only the new objects since the specified memgraph.
all | <classes-pattern>
Print the addresses of all malloc blocks found on the heap in ascending address order, or the addresses of those objects whose full class name is matched by the regular expression <classes-pattern>. The string "all" indicates that the addresses of all blocks should be printed.

The <classes-pattern> regular expression is interpreted as an extended (modern) regular expression as described by the re_format(7) manual page. "malloc" or "non-object" can be used to refer to blocks that are not of any specific type. Examples of valid classes-patterns include:

__NSCFString
 
'NS.*'
 
'__NSCFString|__NSCFArray'
 
'.*(String|Array)'
 
malloc
 
non-object
 
malloc|.*String
 

The <classes-pattern> pattern can be followed by an optional allocation size specifier, which can be one of the following forms. The square brackets are required. The size can include a 'k' suffix for kilobytes, or an 'm' suffix for megabytes:

[size]
 
[lowerBound-upperBound]
 
[lowerBound+]
 
[-upperBound]
 

Examples of <classes-pattern> with size specifications include:

malloc[2048]
// all malloc blocks of size 2048
malloc[1k-8k]
// all malloc blocks between 1k and 8k
CFData[50k+]
// all CFData objects 50k or larger
[-1024]
// all allocations 1024 bytes or less
Do not show object content in -addresses mode.

malloc(3), leaks(1), malloc_history(1), stringdups(1), vmmap(1), DevToolsSecurity(1)

The Xcode developer tools also include Instruments, a graphical application that can give information similar to that provided by heap. The Allocations instrument graphically displays dynamic, real-time information about the object and memory use in an application, including backtraces of where the allocations occurred. The Leaks instrument performs memory leak analysis.

All memory sizes are given in binary-prefixed units. For example, "1K" refers to 1024 bytes.

Feb. 8, 2022 Mac OS X 14