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slabs rather than embedding a singly linked list in the slabs themselves. This has a few advantages: - Better utilization of the slab's memory by not wasting 16-bytes at the front. - Simpler allocation strategy by not having a struct packed at the front. - Avoids paging every allocated slab in just to traverse them for deallocating or dumping stats. The latter is the really nice part. Folks have complained from time to time bitterly that tearing down a BumpPtrAllocator, even if it doesn't run any destructors, pages in all of the memory allocated. Now it won't. =] Also resolves a FIXME with the scaling of the slab sizes. The scaling now disregards specially sized slabs for allocations larger than the threshold. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206147 91177308-0d34-0410-b5e6-96231b3b80d8
Design Of lib/System
====================
The software in this directory is designed to completely shield LLVM from any
and all operating system specific functionality. It is not intended to be a
complete operating system wrapper (such as ACE), but only to provide the
functionality necessary to support LLVM.
The software located here, of necessity, has very specific and stringent design
rules. Violation of these rules means that cracks in the shield could form and
the primary goal of the library is defeated. By consistently using this library,
LLVM becomes more easily ported to new platforms since the only thing requiring
porting is this library.
Complete documentation for the library can be found in the file:
llvm/docs/SystemLibrary.html
or at this URL:
http://llvm.org/docs/SystemLibrary.html
While we recommend that you read the more detailed documentation, for the
impatient, here's a high level summary of the library's requirements.
1. No system header files are to be exposed through the interface.
2. Std C++ and Std C header files are okay to be exposed through the interface.
3. No exposed system-specific functions.
4. No exposed system-specific data.
5. Data in lib/System classes must use only simple C++ intrinsic types.
6. Errors are handled by returning "true" and setting an optional std::string
7. Library must not throw any exceptions, period.
8. Interface functions must not have throw() specifications.
9. No duplicate function impementations are permitted within an operating
system class.
To accomplish these requirements, the library has numerous design criteria that
must be satisfied. Here's a high level summary of the library's design criteria:
1. No unused functionality (only what LLVM needs)
2. High-Level Interfaces
3. Use Opaque Classes
4. Common Implementations
5. Multiple Implementations
6. Minimize Memory Allocation
7. No Virtual Methods