Process heap space is not infinite. Rather, it Memory is a limited resource and can be exhausted. Available memory is typically bounded by the sum of the amount of physical memory and the swap space allocated to the operating system by the administrator. For example, a system with 1GB of physical memory configured with 2GB of swap space may be able to allocate at most 3GB of heap space total to all running processes (minus the size of the operating system itself and the text and data segments of all running processes). Once all virtual memory has been allocated, requests for more memory will fail. As discussed in rule MEM32-C. Detect and handle memory allocation errors, programs that fail to check for and properly handle memory allocation failures will have undefined behavior and are likely to crash when heap space is exhausted. Heap exhaustion can result from
- A memory leak
- An infinite loop
- The program requiring more memory than is present by default in the heap
- Incorrect implementation of common data structures (for example, hash tables or vectors)
- Overall system memory being exhausted, possibly because of other processes
- The maximum size of a process' data segment (set by
setrlimit()) being exceeded
If malloc() is unable to return the requested memory, it returns NULL instead.
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