libtf: initial commit

libtf is to be user-space cooperative threading library similar
to State Threads (http://state-threads.sourceforge.net/), but
with additional support for multiple cores, using better
algorithms and taking advantage of new Linux kernel syscalls
such as eventfd, signalfd and epoll (edge-triggered mode).

Initial implementation has setjmp based user-space context
switching and trivial testcase. Works on Linux/x86.

TFbuild uses ideas from different build systems, namely Kbuild,
but it's inner workings are quite different. All build files are
included (using macro trickery) instead of recursive making. Thus
the build dependency graph is complete and should yield good make
performance. Also parallel stuff should work.

1 files changed, 19 insertions, 0 deletions

diff --git a/DESIGN b/DESIGN
new file mode 100644
index 0000000..2ffc535
--- /dev/null
+++ b/DESIGN
@@ -0,0 +1,19 @@
+SCHEDULER
+- 4-heap (or 2-heap) with linked nodes
+- epoll
+- edge-triggered monitoring for file i/o (no syscalls to modify fdset)
+- signalfd for signal handling
+- eventfd for thread pool wakeup
+
+FIBERS
+- timer node on fiber control data (for delayed heapify; and reuse on timeouts)
+- fd, signal, pid wait struct on stack of wait function
+- fiber_kill can interrupt wait
+
+SCHEDULER <-> THREAD POOL
+- scheduler queues to thread pool array fifo queue,
+    - semaphore protects threads so no underqueueing happens
+    - eventfd notifies scheduler when queue has free space again
+    - head/tail updated atomically and item position recovered
+- thread pool atomically pushes to resume atomic stack and sets eventfd
+    - scheduler thread atomically pops all and updates fiber states