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220c5ca8f4
Most Unix-like operating systems guarantee that the file descriptor is closed after a call to close(2), even if close comes back with EINTR. For these systems, calling close _again_ will either do nothing or close some other file descriptor open(2)'d by another thread. (Linux) However, some operating systems do not have this behavior. They require at least another call to close(2) before guaranteeing that the descriptor is closed. (HP-UX) And some operating systems have an unpredictable blend of the two behaviors! (xnu) Avoid this disaster by blocking all signals before we call close(2). This ensures that a signal will not be delivered to the thread and close(2) will not give us back EINTR. We restore the signal mask once the operation is done. N.B. This isn't a problem on Windows, it doesn't have a notion of EINTR because signals always get delivered to dedicated signal handling threads. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219189 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