1. Introduce channels, which provide an efficient means for IPC;
2. Leverage channels to rewrite pipe, improving the performance (3X),
robustness, and readability.
This pipe rewrite is not done: some more commits will be added to
implement poll and epoll for pipe.
An event can be anything ranging from the exit of a process (interesting
to `wait4`) to the arrival of a blocked signal (interesting to
`sigwaitinfo`), from the completion of a file operation (interesting to
`epoll`) to the change of a file status (interesting to `inotify`).
To meet the event-related demands from various subsystems, this event
subsystem is designed to provide a set of general-purpose primitives:
* `Waiter`, `Waker`, and `WaiterQueue` are primitives to put threads
to sleep and later wake them up.
* `Event`, `Observer`, and `Notifier` are primitives to handle and
broadcast events.
* `WaiterQueueObserver` implements the common pattern of waking up
threads once some interesting events happen.
Socket-related ocalls, e.g, sendto, sendmsg and write, may cause SIGPIPE
in host. Since the ocall is called by libos, this kind of signal should
be handled in libos. We ignore SIGPIPE in host and raise the same signal
in libos if the return value of the above ocalls is EPIPE. In this way
the signal is handled by libos.
Rlimit are now on the same page of memory space limits defined in Occlum.json. Specific
memory size configuration can be set to child process with `prlimit` syscall or using `ulimit`
command in shell script.
Struct sigaction has a field named sa_mask, which specifies the blocked
signals while executing the signal handler. Previously, this field is not
supported. This commit adds this missing feature.
There are scenarios where the available CPUs are less than all the CPUs
on the machine. Therefore, sched_get/setaffinity should be allowed when
the input buffer size is no less than the available CPUs but less than
all the CPUs.
This reverts commit 1e456f025d6b4e34a726180e7a27a04424fe79d1.
This commit results in segmentation fault when the application munmaps
its own stack. Should be committed back after removing the dependency of
sysret on the user space stack.
Before this commit, events like signals and exit_group are handled by
LibOS threads in a cooperative fashion: if the user code executed by a
LibOS thread does not invoke system calls (e.g., a busy loop), then the LibOS
won't have any opportunity to take control and handle events.
With the help from the POSIX signal-based interrupt mechanism of
Occlum's version of Intel SGX SDK, the LibOS can now interrupt the
execution of arbitrary user code in a LibOS thread by sending real-time
POSIX signals (the signal number is 64) to it. These signals are sent by
a helper thread spawn by Occlum PAL. The helper thread periodically
enters into the enclave to check if there are any LibOS threads with
pending events. If any, the helper thread broadcast POSIX signals to
them. When interrupted by a signal, the receiver LibOS thread may be in
one of the two previously problematic states in terms of event handling:
1. Executing non-cooperative user code (e.g., a busy loop). In this
case, the signal will trigger an interrupt handler inside the enclave,
which can then enter the LibOS kernel to deal with any pending events.
2. Executing an OCall that invokes blocking system calls (e.g., futex,
nanosleep, or blocking I/O). In this case, the signal will interrupt the
blocking system call so that the OCall can return back to the enclave.
Thanks to the new interrupt subsystem, some event-based system calls
are made robust. One such example is exit_group. We can now guarantee
that exit_group can force any thread in a process to exit.
The first bug is a race condition when acquiring the lock of a process's
parent. An example code with race condition looks like below:
```rust
let process : ProessRef = current!().process();
let parent : ProcessRef = process.parent();
let parent_guard : SgxMutexGuard<ProesssInner> = parent.inner();
// This assertion may fail because the process's parent may change to another
// process before the lock is acquired
assert!(parent.pid() == process.parent().pid());
```
The second bug is that when a process exits, its children processes are
not transfered to the idle process correctly.
