diff --git a/src/doc/trpl/the-stack-and-the-heap.md b/src/doc/trpl/the-stack-and-the-heap.md index fb778b59a3d..aca736ef2ac 100644 --- a/src/doc/trpl/the-stack-and-the-heap.md +++ b/src/doc/trpl/the-stack-and-the-heap.md @@ -217,18 +217,18 @@ on the heap. The actual value of the box is a structure which has a pointer to it allocates some memory for the heap, and puts `5` there. The memory now looks like this: -| Address | Name | Value | -|-----------------|------|------------------| -| 230 | | 5 | -| ... | ... | ... | -| 1 | y | 42 | -| 0 | x | → 230 | +| Address | Name | Value | +|----------------------|------|------------------------| +| (230) - 1 | | 5 | +| ... | ... | ... | +| 1 | y | 42 | +| 0 | x | → (230) - 1 | -We have 230 in our hypothetical computer with 1GB of RAM. And since +We have (230) - 1 in our hypothetical computer with 1GB of RAM. And since our stack grows from zero, the easiest place to allocate memory is from the other end. So our first value is at the highest place in memory. And the value of the struct at `x` has a [raw pointer][rawpointer] to the place we’ve -allocated on the heap, so the value of `x` is 230, the memory +allocated on the heap, so the value of `x` is (230) - 1, the memory location we’ve asked for. [rawpointer]: raw-pointers.html @@ -244,18 +244,18 @@ layout of a program which has been running for a while now: | Address | Name | Value | |----------------------|------|------------------------| -| 230 | | 5 | -| (230) - 1 | | | +| (230) - 1 | | 5 | | (230) - 2 | | | -| (230) - 3 | | 42 | +| (230) - 3 | | | +| (230) - 4 | | 42 | | ... | ... | ... | -| 3 | y | → (230) - 3 | +| 3 | y | → (230) - 4 | | 2 | y | 42 | | 1 | y | 42 | -| 0 | x | → 230 | +| 0 | x | → (230) - 1 | In this case, we’ve allocated four things on the heap, but deallocated two of -them. There’s a gap between 230 and (230) - 3 which isn’t +them. There’s a gap between (230) - 1 and (230) - 4 which isn’t currently being used. The specific details of how and why this happens depends on what kind of strategy you use to manage the heap. Different programs can use different ‘memory allocators’, which are libraries that manage this for you. @@ -366,29 +366,29 @@ fn main() { First, we call `main()`: -| Address | Name | Value | -|-----------------|------|------------------| -| 230 | | 20 | -| ... | ... | ... | -| 2 | j | → 0 | -| 1 | i | → 230 | -| 0 | h | 3 | +| Address | Name | Value | +|----------------------|------|------------------------| +| (230) - 1 | | 20 | +| ... | ... | ... | +| 2 | j | → 0 | +| 1 | i | → (230) - 1 | +| 0 | h | 3 | We allocate memory for `j`, `i`, and `h`. `i` is on the heap, and so has a value pointing there. Next, at the end of `main()`, `foo()` gets called: -| Address | Name | Value | -|-----------------|------|-----------------| -| 230 | | 20 | -| ... | ... | ... | -| 5 | z | → 4 | -| 4 | y | 10 | -| 3 | x | → 0 | -| 2 | j | → 0 | -| 1 | i | → 230| -| 0 | h | 3 | +| Address | Name | Value | +|----------------------|------|------------------------| +| (230) - 1 | | 20 | +| ... | ... | ... | +| 5 | z | → 4 | +| 4 | y | 10 | +| 3 | x | → 0 | +| 2 | j | → 0 | +| 1 | i | → (230) - 1 | +| 0 | h | 3 | Space gets allocated for `x`, `y`, and `z`. The argument `x` has the same value as `j`, since that’s what we passed it in. It’s a pointer to the `0` address, @@ -396,42 +396,42 @@ since `j` points at `h`. Next, `foo()` calls `baz()`, passing `z`: -| Address | Name | Value | -|-----------------|------|------------------| -| 230 | | 20 | -| ... | ... | ... | -| 7 | g | 100 | -| 6 | f | → 4 | -| 5 | z | → 4 | -| 4 | y | 10 | -| 3 | x | → 0 | -| 2 | j | → 0 | -| 1 | i | → 230 | -| 0 | h | 3 | +| Address | Name | Value | +|----------------------|------|------------------------| +| (230) - 1 | | 20 | +| ... | ... | ... | +| 7 | g | 100 | +| 6 | f | → 4 | +| 5 | z | → 4 | +| 4 | y | 10 | +| 3 | x | → 0 | +| 2 | j | → 0 | +| 1 | i | → (230) - 1 | +| 0 | h | 3 | We’ve allocated memory for `f` and `g`. `baz()` is very short, so when it’s over, we get rid of its stack frame: -| Address | Name | Value | -|-----------------|------|------------------| -| 230 | | 20 | -| ... | ... | ... | -| 5 | z | → 4 | -| 4 | y | 10 | -| 3 | x | → 0 | -| 2 | j | → 0 | -| 1 | i | → 230 | -| 0 | h | 3 | +| Address | Name | Value | +|----------------------|------|------------------------| +| (230) - 1 | | 20 | +| ... | ... | ... | +| 5 | z | → 4 | +| 4 | y | 10 | +| 3 | x | → 0 | +| 2 | j | → 0 | +| 1 | i | → (230) - 1 | +| 0 | h | 3 | Next, `foo()` calls `bar()` with `x` and `z`: | Address | Name | Value | |----------------------|------|------------------------| -| 230 | | 20 | -| (230) - 1 | | 5 | +| (230) - 1 | | 20 | +| (230) - 2 | | 5 | | ... | ... | ... | | 10 | e | → 9 | -| 9 | d | → (230) - 1 | +| 9 | d | → (230) - 2 | | 8 | c | 5 | | 7 | b | → 4 | | 6 | a | → 0 | @@ -439,24 +439,24 @@ Next, `foo()` calls `bar()` with `x` and `z`: | 4 | y | 10 | | 3 | x | → 0 | | 2 | j | → 0 | -| 1 | i | → 230 | +| 1 | i | → (230) - 1 | | 0 | h | 3 | We end up allocating another value on the heap, and so we have to subtract one -from 230. It’s easier to just write that than `1,073,741,823`. In any +from (230) - 1. It’s easier to just write that than `1,073,741,822`. In any case, we set up the variables as usual. At the end of `bar()`, it calls `baz()`: | Address | Name | Value | |----------------------|------|------------------------| -| 230 | | 20 | -| (230) - 1 | | 5 | +| (230) - 1 | | 20 | +| (230) - 2 | | 5 | | ... | ... | ... | | 12 | g | 100 | | 11 | f | → 9 | | 10 | e | → 9 | -| 9 | d | → (230) - 1 | +| 9 | d | → (230) - 2 | | 8 | c | 5 | | 7 | b | → 4 | | 6 | a | → 0 | @@ -464,7 +464,7 @@ At the end of `bar()`, it calls `baz()`: | 4 | y | 10 | | 3 | x | → 0 | | 2 | j | → 0 | -| 1 | i | → 230 | +| 1 | i | → (230) - 1 | | 0 | h | 3 | With this, we’re at our deepest point! Whew! Congrats for following along this @@ -474,11 +474,11 @@ After `baz()` is over, we get rid of `f` and `g`: | Address | Name | Value | |----------------------|------|------------------------| -| 230 | | 20 | -| (230) - 1 | | 5 | +| (230) - 1 | | 20 | +| (230) - 2 | | 5 | | ... | ... | ... | | 10 | e | → 9 | -| 9 | d | → (230) - 1 | +| 9 | d | → (230) - 2 | | 8 | c | 5 | | 7 | b | → 4 | | 6 | a | → 0 | @@ -486,32 +486,32 @@ After `baz()` is over, we get rid of `f` and `g`: | 4 | y | 10 | | 3 | x | → 0 | | 2 | j | → 0 | -| 1 | i | → 230 | +| 1 | i | → (230) - 1 | | 0 | h | 3 | Next, we return from `bar()`. `d` in this case is a `Box`, so it also frees -what it points to: (230) - 1. +what it points to: (230) - 2. -| Address | Name | Value | -|-----------------|------|------------------| -| 230 | | 20 | -| ... | ... | ... | -| 5 | z | → 4 | -| 4 | y | 10 | -| 3 | x | → 0 | -| 2 | j | → 0 | -| 1 | i | → 230 | -| 0 | h | 3 | +| Address | Name | Value | +|----------------------|------|------------------------| +| (230) - 1 | | 20 | +| ... | ... | ... | +| 5 | z | → 4 | +| 4 | y | 10 | +| 3 | x | → 0 | +| 2 | j | → 0 | +| 1 | i | → (230) - 1 | +| 0 | h | 3 | And after that, `foo()` returns: -| Address | Name | Value | -|-----------------|------|------------------| -| 230 | | 20 | -| ... | ... | ... | -| 2 | j | → 0 | -| 1 | i | → 230 | -| 0 | h | 3 | +| Address | Name | Value | +|----------------------|------|------------------------| +| (230) - 1 | | 20 | +| ... | ... | ... | +| 2 | j | → 0 | +| 1 | i | → (230) - 1 | +| 0 | h | 3 | And then, finally, `main()`, which cleans the rest up. When `i` is `Drop`ped, it will clean up the last of the heap too.