67 lines
2.5 KiB
Markdown
67 lines
2.5 KiB
Markdown
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---
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id: 1fig
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tags: [memory]
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created: Tuesday, April 16, 2024
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---
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# Stack memory
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## Summary
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- Along with [[Heap_memory|heap memory]] heap memory, programs make use of
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_stack memory_ during runtime.
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- Best suited for small-sized singular values that are temporary/ephemeral
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rather than large or complex data types that need to persist for a longer
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time.
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- Specifically used to keep track of memory used during function executions
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within a given scope: control flow, local variables, returned value.
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- Uses a LIFO data-structure
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Similarly to the [[Stacks|stack data structure]], it works on the basis of LIFO:
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the last item put on the stack is the first item to be withdrawn.
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Note, this doesn't mean that the data at the memory addresses that comprise the
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stack can _only_ be accessed in a LIFO manner. Any item currently on the stack
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can be accessed (be read or modified) at any time. LIFO applies when it is is
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time to clear memory from the stack: the most recent addition is cleared first
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from the top down.
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### Stack pointer
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A **stack pointer** is used to manage the items in the stack. This value is
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stored in a [[CPU_architecture#registers|register]] and its value is the memory
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address of the item currently on the top of the stack. Note: _not_ the value
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itself, the _address_ of the value.
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When a new value is added to the top of the stack, the pointer's value is
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adjusted to increase the size of the stack and make room for the new value. So
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this will be a new memory address for the latest item. When an item is removed,
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the reverse happens. The previously top address is cleared and the pointer
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points to the new top item.
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## Threads
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For every thread that a program spawns, it gets its own stack or "stack frame".
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Stack memory within the thread can only be accessed by processes within that
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thread which is what makes it well suited for managing scoped function memory.
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### Role in program execution
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1. Function call management: a stack records the key information pertaining to
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the execution of a function: parameters, local variables, the location of the
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address for the returned value.
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2. Local variable storage: storing the variables local to a function's scope and
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removing them once the function returns, avoiding
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[[Memory_leaks|memory leaks]]
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3. Control flow: record from where a function is called and where its return
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value should be stored, meaning the right value is always returned no matter
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how nested it is.
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4. Recursion: individuating each call of a function that calls itself and its
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given step to avoid infinite loops
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