Google's Chromium sandbox

Nah, the parent and gdb hand off. Whenever the child process sends a request for a system call, that trips a breakpoint, and gdb lets go of the child, which stalls waiting on the parent. Gdb attaches to the parent, and the parent attaches to the child and does its business. When the system call is done, the parent releases its ptrace and hits a breakpoint of its own, and then gdb parks the parent on a read call, detaches from the parent and re-attaches to the child, has it send a wakeup to the parent, and then we're back where we started.