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std.Mutex: implement blocking mutexes on linux

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closes #1463

Thanks to Shawn Landden for the original pull request.
This commit is based on that code.
This commit is contained in:
Andrew Kelley 2018-10-03 13:19:10 -04:00
parent acefcdbca5
commit 66cb75d114
No known key found for this signature in database
GPG Key ID: 4E7CD66038A4D47C
7 changed files with 107 additions and 25 deletions
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1
CMakeLists.txt
View File

@ -635,6 +635,7 @@ set(ZIG_STD_FILES
"special/init-lib/src/main.zig"
"special/panic.zig"
"special/test_runner.zig"
"spinlock.zig"
"unicode.zig"
"zig/ast.zig"
"zig/index.zig"

14
std/event/loop.zig
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@ -736,8 +736,8 @@ pub const Loop = struct {
_ = os.bsdKEvent(self.os_data.fs_kqfd, fs_kevs, empty_kevs, null) catch unreachable;
},
builtin.Os.linux => {
_ = @atomicRmw(u8, &self.os_data.fs_queue_item, AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst);
const rc = os.linux.futex_wake(@ptrToInt(&self.os_data.fs_queue_item), os.linux.FUTEX_WAKE, 1);
_ = @atomicRmw(i32, &self.os_data.fs_queue_item, AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst);
const rc = os.linux.futex_wake(&self.os_data.fs_queue_item, os.linux.FUTEX_WAKE, 1);
switch (os.linux.getErrno(rc)) {
0 => {},
posix.EINVAL => unreachable,
@ -757,7 +757,7 @@ pub const Loop = struct {
fn posixFsRun(self: *Loop) void {
while (true) {
if (builtin.os == builtin.Os.linux) {
_ = @atomicRmw(u8, &self.os_data.fs_queue_item, AtomicRmwOp.Xchg, 0, AtomicOrder.SeqCst);
_ = @atomicRmw(i32, &self.os_data.fs_queue_item, AtomicRmwOp.Xchg, 0, AtomicOrder.SeqCst);
}
while (self.os_data.fs_queue.get()) |node| {
switch (node.data.msg) {
@ -794,11 +794,9 @@ pub const Loop = struct {
}
switch (builtin.os) {
builtin.Os.linux => {
const rc = os.linux.futex_wait(@ptrToInt(&self.os_data.fs_queue_item), os.linux.FUTEX_WAIT, 0, null);
const rc = os.linux.futex_wait(&self.os_data.fs_queue_item, os.linux.FUTEX_WAIT, 0, null);
switch (os.linux.getErrno(rc)) {
0 => continue,
posix.EINTR => continue,
posix.EAGAIN => continue,
0, posix.EINTR, posix.EAGAIN => continue,
else => unreachable,
}
},
@ -838,7 +836,7 @@ pub const Loop = struct {
final_eventfd: i32,
final_eventfd_event: os.linux.epoll_event,
fs_thread: *os.Thread,
fs_queue_item: u8,
fs_queue_item: i32,
fs_queue: std.atomic.Queue(fs.Request),
fs_end_request: fs.RequestNode,
};

16
std/index.zig
View File

@ -1,15 +1,16 @@
pub const ArrayList = @import("array_list.zig").ArrayList;
pub const AlignedArrayList = @import("array_list.zig").AlignedArrayList;
pub const ArrayList = @import("array_list.zig").ArrayList;
pub const AutoHashMap = @import("hash_map.zig").AutoHashMap;
pub const BufMap = @import("buf_map.zig").BufMap;
pub const BufSet = @import("buf_set.zig").BufSet;
pub const Buffer = @import("buffer.zig").Buffer;
pub const BufferOutStream = @import("io.zig").BufferOutStream;
pub const HashMap = @import("hash_map.zig").HashMap;
pub const AutoHashMap = @import("hash_map.zig").AutoHashMap;
pub const LinkedList = @import("linked_list.zig").LinkedList;
pub const SegmentedList = @import("segmented_list.zig").SegmentedList;
pub const DynLib = @import("dynamic_library.zig").DynLib;
pub const HashMap = @import("hash_map.zig").HashMap;
pub const LinkedList = @import("linked_list.zig").LinkedList;
pub const Mutex = @import("mutex.zig").Mutex;
pub const SegmentedList = @import("segmented_list.zig").SegmentedList;
pub const SpinLock = @import("spinlock.zig").SpinLock;
pub const atomic = @import("atomic/index.zig");
pub const base64 = @import("base64.zig");
@ -45,15 +46,16 @@ pub const lazyInit = @import("lazy_init.zig").lazyInit;
test "std" {
// run tests from these
_ = @import("atomic/index.zig");
_ = @import("array_list.zig");
_ = @import("atomic/index.zig");
_ = @import("buf_map.zig");
_ = @import("buf_set.zig");
_ = @import("buffer.zig");
_ = @import("hash_map.zig");
_ = @import("linked_list.zig");
_ = @import("segmented_list.zig");
_ = @import("mutex.zig");
_ = @import("segmented_list.zig");
_ = @import("spinlock.zig");
_ = @import("base64.zig");
_ = @import("build.zig");

59
std/mutex.zig
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@ -3,25 +3,74 @@ const builtin = @import("builtin");
const AtomicOrder = builtin.AtomicOrder;
const AtomicRmwOp = builtin.AtomicRmwOp;
const assert = std.debug.assert;
const SpinLock = std.SpinLock;
const linux = std.os.linux;
/// TODO use syscalls instead of a spinlock
/// Lock may be held only once. If the same thread
/// tries to acquire the same mutex twice, it deadlocks.
pub const Mutex = struct {
lock: u8, // TODO use a bool
/// 0: unlocked
/// 1: locked, no waiters
/// 2: locked, one or more waiters
linux_lock: @typeOf(linux_lock_init),
/// TODO better implementation than spin lock
spin_lock: @typeOf(spin_lock_init),
const linux_lock_init = if (builtin.os == builtin.Os.linux) i32(0) else {};
const spin_lock_init = if (builtin.os != builtin.Os.linux) SpinLock.init() else {};
pub const Held = struct {
mutex: *Mutex,
pub fn release(self: Held) void {
assert(@atomicRmw(u8, &self.mutex.lock, builtin.AtomicRmwOp.Xchg, 0, AtomicOrder.SeqCst) == 1);
if (builtin.os == builtin.Os.linux) {
// Always unlock. If the previous state was Locked-No-Waiters, then we're done.
// Otherwise, wake a waiter up.
const prev = @atomicRmw(i32, &self.mutex.linux_lock, AtomicRmwOp.Xchg, 0, AtomicOrder.Release);
if (prev != 1) {
assert(prev == 2);
const rc = linux.futex_wake(&self.mutex.linux_lock, linux.FUTEX_WAKE, 1);
switch (linux.getErrno(rc)) {
0 => {},
linux.EINVAL => unreachable,
else => unreachable,
}
}
} else {
SpinLock.Held.release(SpinLock.Held{ .spinlock = &self.mutex.spin_lock });
}
}
};
pub fn init() Mutex {
return Mutex{ .lock = 0 };
return Mutex{
.linux_lock = linux_lock_init,
.spin_lock = spin_lock_init,
};
}
pub fn acquire(self: *Mutex) Held {
while (@atomicRmw(u8, &self.lock, builtin.AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst) != 0) {}
if (builtin.os == builtin.Os.linux) {
// First try to go from Unlocked to Locked-No-Waiters. If this succeeds, no syscalls are needed.
// Otherwise, we need to be in the Locked-With-Waiters state. If we are already in that state,
// proceed to futex_wait. Otherwise, try to go from Locked-No-Waiters to Locked-With-Waiters.
// If that succeeds, proceed to futex_wait. Otherwise start the whole loop over again.
while (@cmpxchgWeak(i32, &self.linux_lock, 0, 1, AtomicOrder.Acquire, AtomicOrder.Monotonic)) |l| {
if (l == 2 or
@cmpxchgWeak(i32, &self.linux_lock, 1, 2, AtomicOrder.Acquire, AtomicOrder.Monotonic) == null)
{
const rc = linux.futex_wait(&self.linux_lock, linux.FUTEX_WAIT, 2, null);
switch (linux.getErrno(rc)) {
0, linux.EINTR, linux.EAGAIN => continue,
linux.EINVAL => unreachable,
else => unreachable,
}
}
}
} else {
_ = self.spin_lock.acquire();
}
return Held{ .mutex = self };
}
};

2
std/os/index.zig
View File

@ -2839,7 +2839,7 @@ pub const Thread = struct {
while (true) {
const pid_value = @atomicLoad(i32, &self.data.handle, builtin.AtomicOrder.SeqCst);
if (pid_value == 0) break;
const rc = linux.futex_wait(@ptrToInt(&self.data.handle), linux.FUTEX_WAIT, pid_value, null);
const rc = linux.futex_wait(&self.data.handle, linux.FUTEX_WAIT, pid_value, null);
switch (linux.getErrno(rc)) {
0 => continue,
posix.EINTR => continue,

8
std/os/linux/index.zig
View File

@ -728,12 +728,12 @@ pub inline fn vfork() usize {
return @inlineCall(syscall0, SYS_vfork);
}
pub fn futex_wait(uaddr: usize, futex_op: u32, val: i32, timeout: ?*timespec) usize {
return syscall4(SYS_futex, uaddr, futex_op, @bitCast(u32, val), @ptrToInt(timeout));
pub fn futex_wait(uaddr: *const i32, futex_op: u32, val: i32, timeout: ?*timespec) usize {
return syscall4(SYS_futex, @ptrToInt(uaddr), futex_op, @bitCast(u32, val), @ptrToInt(timeout));
}
pub fn futex_wake(uaddr: usize, futex_op: u32, val: i32) usize {
return syscall3(SYS_futex, uaddr, futex_op, @bitCast(u32, val));
pub fn futex_wake(uaddr: *const i32, futex_op: u32, val: i32) usize {
return syscall3(SYS_futex, @ptrToInt(uaddr), futex_op, @bitCast(u32, val));
}
pub fn getcwd(buf: [*]u8, size: usize) usize {

32
std/spinlock.zig Normal file
View File

@ -0,0 +1,32 @@
const std = @import("index.zig");
const builtin = @import("builtin");
const AtomicOrder = builtin.AtomicOrder;
const AtomicRmwOp = builtin.AtomicRmwOp;
const assert = std.debug.assert;
pub const SpinLock = struct {
lock: u8, // TODO use a bool or enum
pub const Held = struct {
spinlock: *SpinLock,
pub fn release(self: Held) void {
assert(@atomicRmw(u8, &self.spinlock.lock, builtin.AtomicRmwOp.Xchg, 0, AtomicOrder.SeqCst) == 1);
}
};
pub fn init() SpinLock {
return SpinLock{ .lock = 0 };
}
pub fn acquire(self: *SpinLock) Held {
while (@atomicRmw(u8, &self.lock, builtin.AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst) != 0) {}
return Held{ .spinlock = self };
}
};
test "spinlock" {
var lock = SpinLock.init();
const held = lock.acquire();
defer held.release();
}