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// Written in the D programming language.
/**
D's built-in garbage-collected allocator.
Source: $(PHOBOSSRC std/experimental/allocator/_gc_allocator.d)
*/
module std.experimental.allocator.gc_allocator;
import std.experimental.allocator.common;
/**
D's built-in garbage-collected allocator.
*/
struct GCAllocator
{
import core.memory : GC;
import std.typecons : Ternary;
version (StdUnittest) @system unittest { testAllocator!(() => GCAllocator.instance); }
/**
The alignment is a static constant equal to `platformAlignment`, which
ensures proper alignment for any D data type.
*/
enum uint alignment = platformAlignment;
/**
Standard allocator methods per the semantics defined above. The $(D
deallocate) and `reallocate` methods are `@system` because they may
move memory around, leaving dangling pointers in user code.
*/
pure nothrow @trusted void[] allocate(size_t bytes) shared const
{
if (!bytes) return null;
auto p = GC.malloc(bytes);
return p ? p[0 .. bytes] : null;
}
/// Ditto
pure nothrow @trusted bool expand(ref void[] b, size_t delta) shared const
{
if (delta == 0) return true;
if (b is null) return false;
immutable curLength = GC.sizeOf(b.ptr);
assert(curLength != 0); // we have a valid GC pointer here
immutable desired = b.length + delta;
if (desired > curLength) // check to see if the current block can't hold the data
{
immutable sizeRequest = desired - curLength;
immutable newSize = GC.extend(b.ptr, sizeRequest, sizeRequest);
if (newSize == 0)
{
// expansion unsuccessful
return false;
}
assert(newSize >= desired);
}
b = b.ptr[0 .. desired];
return true;
}
/// Ditto
pure nothrow @system bool reallocate(ref void[] b, size_t newSize) shared const
{
import core.exception : OutOfMemoryError;
try
{
auto p = cast(ubyte*) GC.realloc(b.ptr, newSize);
b = p[0 .. newSize];
}
catch (OutOfMemoryError)
{
// leave the block in place, tell caller
return false;
}
return true;
}
/// Ditto
pure nothrow @trusted @nogc
Ternary resolveInternalPointer(const void* p, ref void[] result) shared const
{
auto r = GC.addrOf(cast(void*) p);
if (!r) return Ternary.no;
result = r[0 .. GC.sizeOf(r)];
return Ternary.yes;
}
/// Ditto
pure nothrow @system @nogc
bool deallocate(void[] b) shared const
{
GC.free(b.ptr);
return true;
}
/// Ditto
pure nothrow @safe @nogc
size_t goodAllocSize(size_t n) shared const
{
if (n == 0)
return 0;
if (n <= 16)
return 16;
import core.bitop : bsr;
auto largestBit = bsr(n-1) + 1;
if (largestBit <= 12) // 4096 or less
return size_t(1) << largestBit;
// larger, we use a multiple of 4096.
return ((n + 4095) / 4096) * 4096;
}
package pure nothrow @trusted void[] allocateZeroed()(size_t bytes) shared const
{
if (!bytes) return null;
auto p = GC.calloc(bytes);
return p ? p[0 .. bytes] : null;
}
/**
Returns the global instance of this allocator type. The garbage collected
allocator is thread-safe, therefore all of its methods and `instance` itself
are `shared`.
*/
static shared const GCAllocator instance;
// Leave it undocummented for now.
nothrow @trusted void collect() shared const
{
GC.collect();
}
}
///
pure @system unittest
{
auto buffer = GCAllocator.instance.allocate(1024 * 1024 * 4);
// deallocate upon scope's end (alternatively: leave it to collection)
scope(exit) GCAllocator.instance.deallocate(buffer);
//...
}
pure @safe unittest
{
auto b = GCAllocator.instance.allocate(10_000);
assert(GCAllocator.instance.expand(b, 1));
}
pure @system unittest
{
import core.memory : GC;
import std.typecons : Ternary;
// test allocation sizes
assert((() nothrow @safe @nogc => GCAllocator.instance.goodAllocSize(1))() == 16);
for (size_t s = 16; s <= 8192; s *= 2)
{
assert((() nothrow @safe @nogc => GCAllocator.instance.goodAllocSize(s))() == s);
assert((() nothrow @safe @nogc => GCAllocator.instance.goodAllocSize(s - (s / 2) + 1))() == s);
auto buffer = GCAllocator.instance.allocate(s);
scope(exit) () nothrow @nogc { GCAllocator.instance.deallocate(buffer); }();
void[] p;
assert((() nothrow @safe => GCAllocator.instance.resolveInternalPointer(null, p))() == Ternary.no);
assert((() nothrow @safe => GCAllocator.instance.resolveInternalPointer(&buffer[0], p))() == Ternary.yes);
assert(p.ptr is buffer.ptr && p.length >= buffer.length);
assert(GC.sizeOf(buffer.ptr) == s);
// the GC should provide power of 2 as "good" sizes, but other sizes are allowed, too
version (none)
{
auto buffer2 = GCAllocator.instance.allocate(s - (s / 2) + 1);
scope(exit) () nothrow @nogc { GCAllocator.instance.deallocate(buffer2); }();
assert(GC.sizeOf(buffer2.ptr) == s);
}
}
// anything above a page is simply rounded up to next page
assert((() nothrow @safe @nogc => GCAllocator.instance.goodAllocSize(4096 * 4 + 1))() == 4096 * 5);
}
pure nothrow @safe unittest
{
import std.typecons : Ternary;
void[] buffer = GCAllocator.instance.allocate(42);
void[] result;
Ternary found = GCAllocator.instance.resolveInternalPointer(&buffer[0], result);
assert(found == Ternary.yes && &result[0] == &buffer[0] && result.length >= buffer.length);
assert(GCAllocator.instance.resolveInternalPointer(null, result) == Ternary.no);
void *badPtr = (() @trusted => cast(void*)(0xdeadbeef))();
assert(GCAllocator.instance.resolveInternalPointer(badPtr, result) == Ternary.no);
}
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