v/vlib/sync/channels.v

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module sync
import time
import rand
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$if windows {
#flag -I @VROOT/thirdparty/stdatomic/win
} $else {
#flag -I @VROOT/thirdparty/stdatomic/nix
}
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$if linux {
$if tinyc {
// most Linux distributions have /usr/lib/libatomic.so, but Ubuntu uses gcc version specific dir
#flag -L/usr/lib/gcc/x86_64-linux-gnu/6
#flag -L/usr/lib/gcc/x86_64-linux-gnu/7
#flag -L/usr/lib/gcc/x86_64-linux-gnu/8
#flag -L/usr/lib/gcc/x86_64-linux-gnu/9
#flag -L/usr/lib/gcc/x86_64-linux-gnu/10
#flag -L/usr/lib/gcc/x86_64-linux-gnu/11
#flag -L/usr/lib/gcc/x86_64-linux-gnu/12
#flag -latomic
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}
}
#include <atomic.h>
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// The following functions are actually generic in C
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fn C.atomic_load_ptr(voidptr) voidptr
fn C.atomic_store_ptr(voidptr, voidptr)
fn C.atomic_compare_exchange_weak_ptr(voidptr, voidptr, voidptr) bool
fn C.atomic_compare_exchange_strong_ptr(voidptr, voidptr, voidptr) bool
fn C.atomic_exchange_ptr(voidptr, voidptr) voidptr
fn C.atomic_fetch_add_ptr(voidptr, voidptr) voidptr
fn C.atomic_fetch_sub_ptr(voidptr, voidptr) voidptr
fn C.atomic_load_u16(voidptr) u16
fn C.atomic_store_u16(voidptr, u16)
fn C.atomic_compare_exchange_weak_u16(voidptr, voidptr, u16) bool
fn C.atomic_compare_exchange_strong_u16(voidptr, voidptr, u16) bool
fn C.atomic_exchange_u16(voidptr, u16) u16
fn C.atomic_fetch_add_u16(voidptr, u16) u16
fn C.atomic_fetch_sub_u16(voidptr, u16) u16
fn C.atomic_load_u32(voidptr) u32
fn C.atomic_store_u32(voidptr, u32)
fn C.atomic_compare_exchange_weak_u32(voidptr, voidptr, u32) bool
fn C.atomic_compare_exchange_strong_u32(voidptr, voidptr, u32) bool
fn C.atomic_exchange_u32(voidptr, u32) u32
fn C.atomic_fetch_add_u32(voidptr, u32) u32
fn C.atomic_fetch_sub_u32(voidptr, u32) u32
fn C.atomic_load_u64(voidptr) u64
fn C.atomic_store_u64(voidptr, u64)
fn C.atomic_compare_exchange_weak_u64(voidptr, voidptr, u64) bool
fn C.atomic_compare_exchange_strong_u64(voidptr, voidptr, u64) bool
fn C.atomic_exchange_u64(voidptr, u64) u64
fn C.atomic_fetch_add_u64(voidptr, u64) u64
fn C.atomic_fetch_sub_u64(voidptr, u64) u64
const (
// how often to try to get data without blocking before to wait for semaphore
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spinloops = 750
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spinloops_sem = 4000
)
enum BufferElemStat {
unused = 0
writing
written
reading
}
struct Subscription {
mut:
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sem &Semaphore
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prev &&Subscription
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nxt &Subscription
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}
enum Direction {
pop
push
}
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struct Channel {
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ringbuf &byte // queue for buffered channels
statusbuf &byte // flags to synchronize write/read in ringbuf
objsize u32
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mut: // atomic
writesem Semaphore // to wake thread that wanted to write, but buffer was full
readsem Semaphore // to wake thread that wanted to read, but buffer was empty
writesem_im Semaphore
readsem_im Semaphore
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write_adr C.atomic_uintptr_t // if != NULL the next obj can be written here without wait
read_adr C.atomic_uintptr_t // if != NULL an obj can be read from here without wait
adr_read C.atomic_uintptr_t // used to identify origin of writesem
adr_written C.atomic_uintptr_t // used to identify origin of readsem
write_free u32 // for queue state
read_avail u32
buf_elem_write_idx u32
buf_elem_read_idx u32
// for select
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write_subscriber &Subscription
read_subscriber &Subscription
write_sub_mtx u16
read_sub_mtx u16
closed u16
pub:
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cap u32 // queue length in #objects
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}
pub fn new_channel<T>(n u32) &Channel {
st := sizeof(T)
return new_channel_st(n, st)
}
fn new_channel_st(n u32, st u32) &Channel {
wsem := if n > 0 { n } else { 1 }
rsem := if n > 0 { u32(0) } else { 1 }
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rbuf := if n > 0 { unsafe { malloc(int(n * st)) } } else { &byte(0) }
sbuf := if n > 0 { vcalloc(int(n * 2)) } else { &byte(0) }
mut ch := &Channel{
objsize: st
cap: n
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write_free: n
read_avail: 0
ringbuf: rbuf
statusbuf: sbuf
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write_subscriber: 0
read_subscriber: 0
}
ch.writesem.init(wsem)
ch.readsem.init(rsem)
ch.writesem_im.init(0)
ch.readsem_im.init(0)
return ch
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}
pub fn (mut ch Channel) close() {
open_val := u16(0)
if !C.atomic_compare_exchange_strong_u16(&ch.closed, &open_val, 1) {
return
}
mut nulladr := voidptr(0)
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for !C.atomic_compare_exchange_weak_ptr(unsafe { &voidptr(&ch.adr_written) }, &nulladr,
voidptr(-1)) {
nulladr = voidptr(0)
}
ch.readsem_im.post()
ch.readsem.post()
mut null16 := u16(0)
for !C.atomic_compare_exchange_weak_u16(&ch.read_sub_mtx, &null16, u16(1)) {
null16 = u16(0)
}
if ch.read_subscriber != voidptr(0) {
ch.read_subscriber.sem.post()
}
C.atomic_store_u16(&ch.read_sub_mtx, u16(0))
null16 = u16(0)
for !C.atomic_compare_exchange_weak_u16(&ch.write_sub_mtx, &null16, u16(1)) {
null16 = u16(0)
}
if ch.write_subscriber != voidptr(0) {
ch.write_subscriber.sem.post()
}
C.atomic_store_u16(&ch.write_sub_mtx, u16(0))
ch.writesem.post()
if ch.cap == 0 {
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C.atomic_store_ptr(unsafe { &voidptr(&ch.read_adr) }, voidptr(0))
}
ch.writesem_im.post()
}
[inline]
pub fn (mut ch Channel) len() int {
return int(C.atomic_load_u32(&ch.read_avail))
}
[inline]
pub fn (mut ch Channel) closed() bool {
return C.atomic_load_u16(&ch.closed) != 0
}
[inline]
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pub fn (mut ch Channel) push(src voidptr) {
if ch.try_push_priv(src, false) == .closed {
panic('push on closed channel')
}
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}
[inline]
pub fn (mut ch Channel) try_push(src voidptr) ChanState {
return ch.try_push_priv(src, true)
}
fn (mut ch Channel) try_push_priv(src voidptr, no_block bool) ChanState {
if C.atomic_load_u16(&ch.closed) != 0 {
return .closed
}
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spinloops_sem_, spinloops_ := if no_block { 1, 1 } else { sync.spinloops, sync.spinloops_sem }
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mut have_swapped := false
for {
mut got_sem := false
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mut wradr := C.atomic_load_ptr(unsafe { &voidptr(&ch.write_adr) })
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for wradr != C.NULL {
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if C.atomic_compare_exchange_strong_ptr(unsafe { &voidptr(&ch.write_adr) },
&wradr, voidptr(0))
{
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// there is a reader waiting for us
unsafe { C.memcpy(wradr, src, ch.objsize) }
mut nulladr := voidptr(0)
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for !C.atomic_compare_exchange_weak_ptr(unsafe { &voidptr(&ch.adr_written) },
&nulladr, wradr) {
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nulladr = voidptr(0)
}
ch.readsem_im.post()
return .success
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}
}
if no_block && ch.cap == 0 {
return .not_ready
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}
// get token to read
for _ in 0 .. spinloops_sem_ {
if got_sem {
break
}
got_sem = ch.writesem.try_wait()
}
if !got_sem {
if no_block {
return .not_ready
}
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ch.writesem.wait()
}
if C.atomic_load_u16(&ch.closed) != 0 {
ch.writesem.post()
return .closed
}
if ch.cap == 0 {
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// try to advertise current object as readable
mut read_in_progress := false
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C.atomic_store_ptr(unsafe { &voidptr(&ch.read_adr) }, src)
wradr = C.atomic_load_ptr(unsafe { &voidptr(&ch.write_adr) })
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if wradr != C.NULL {
mut src2 := src
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if C.atomic_compare_exchange_strong_ptr(unsafe { &voidptr(&ch.read_adr) },
&src2, voidptr(0))
{
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ch.writesem.post()
continue
} else {
read_in_progress = true
}
}
if !read_in_progress {
mut null16 := u16(0)
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for !C.atomic_compare_exchange_weak_u16(voidptr(&ch.read_sub_mtx), &null16,
u16(1)) {
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null16 = u16(0)
}
if ch.read_subscriber != voidptr(0) {
ch.read_subscriber.sem.post()
}
C.atomic_store_u16(&ch.read_sub_mtx, u16(0))
}
mut src2 := src
for sp := u32(0); sp < spinloops_ || read_in_progress; sp++ {
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if C.atomic_compare_exchange_strong_ptr(unsafe { &voidptr(&ch.adr_read) },
&src2, voidptr(0))
{
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have_swapped = true
read_in_progress = true
break
}
src2 = src
}
mut got_im_sem := false
for sp := u32(0); sp < spinloops_sem_ || read_in_progress; sp++ {
got_im_sem = ch.writesem_im.try_wait()
if got_im_sem {
break
}
}
for {
if got_im_sem {
got_im_sem = false
} else {
ch.writesem_im.wait()
}
if C.atomic_load_u16(&ch.closed) != 0 {
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if have_swapped
|| C.atomic_compare_exchange_strong_ptr(unsafe { &voidptr(&ch.adr_read) }, &src2, voidptr(0)) {
ch.writesem.post()
return .success
} else {
return .closed
}
}
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if have_swapped
|| C.atomic_compare_exchange_strong_ptr(unsafe { &voidptr(&ch.adr_read) }, &src2, voidptr(0)) {
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ch.writesem.post()
break
} else {
// this semaphore was not for us - repost in
ch.writesem_im.post()
if src2 == voidptr(-1) {
ch.readsem.post()
return .closed
}
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src2 = src
}
}
return .success
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} else {
// buffered channel
mut space_in_queue := false
mut wr_free := C.atomic_load_u32(&ch.write_free)
for wr_free > 0 {
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space_in_queue = C.atomic_compare_exchange_weak_u32(&ch.write_free, &wr_free,
wr_free - 1)
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if space_in_queue {
break
}
}
if space_in_queue {
mut wr_idx := C.atomic_load_u32(&ch.buf_elem_write_idx)
for {
mut new_wr_idx := wr_idx + 1
for new_wr_idx >= ch.cap {
new_wr_idx -= ch.cap
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}
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if C.atomic_compare_exchange_strong_u32(&ch.buf_elem_write_idx, &wr_idx,
new_wr_idx)
{
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break
}
}
mut wr_ptr := ch.ringbuf
mut status_adr := ch.statusbuf
unsafe {
wr_ptr += wr_idx * ch.objsize
status_adr += wr_idx * sizeof(u16)
}
mut expected_status := u16(BufferElemStat.unused)
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for !C.atomic_compare_exchange_weak_u16(unsafe { &u16(status_adr) },
&expected_status, u16(BufferElemStat.writing)) {
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expected_status = u16(BufferElemStat.unused)
}
unsafe {
C.memcpy(wr_ptr, src, ch.objsize)
}
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C.atomic_store_u16(unsafe { &u16(status_adr) }, u16(BufferElemStat.written))
C.atomic_fetch_add_u32(&ch.read_avail, 1)
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ch.readsem.post()
mut null16 := u16(0)
for !C.atomic_compare_exchange_weak_u16(&ch.read_sub_mtx, &null16, u16(1)) {
null16 = u16(0)
}
if ch.read_subscriber != voidptr(0) {
ch.read_subscriber.sem.post()
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}
C.atomic_store_u16(&ch.read_sub_mtx, u16(0))
return .success
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} else {
if no_block {
return .not_ready
}
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ch.writesem.post()
}
}
}
// we should not get here but the V compiler want's to see a return statement
assert false
return .success
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}
[inline]
pub fn (mut ch Channel) pop(dest voidptr) bool {
return ch.try_pop_priv(dest, false) == .success
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}
[inline]
pub fn (mut ch Channel) try_pop(dest voidptr) ChanState {
return ch.try_pop_priv(dest, true)
}
fn (mut ch Channel) try_pop_priv(dest voidptr, no_block bool) ChanState {
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spinloops_sem_, spinloops_ := if no_block { 1, 1 } else { sync.spinloops, sync.spinloops_sem }
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mut have_swapped := false
mut write_in_progress := false
for {
mut got_sem := false
if ch.cap == 0 {
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// unbuffered channel - first see if a `push()` has adversized
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mut rdadr := C.atomic_load_ptr(unsafe { &voidptr(&ch.read_adr) })
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for rdadr != C.NULL {
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if C.atomic_compare_exchange_strong_ptr(unsafe { &voidptr(&ch.read_adr) },
&rdadr, voidptr(0))
{
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// there is a writer waiting for us
unsafe { C.memcpy(dest, rdadr, ch.objsize) }
mut nulladr := voidptr(0)
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for !C.atomic_compare_exchange_weak_ptr(unsafe { &voidptr(&ch.adr_read) },
&nulladr, rdadr) {
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nulladr = voidptr(0)
}
ch.writesem_im.post()
return .success
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}
}
if no_block {
if C.atomic_load_u16(&ch.closed) == 0 {
return .not_ready
} else {
return .closed
}
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}
}
// get token to read
for _ in 0 .. spinloops_sem_ {
if got_sem {
break
}
got_sem = ch.readsem.try_wait()
}
if !got_sem {
if no_block {
if C.atomic_load_u16(&ch.closed) == 0 {
return .not_ready
} else {
return .closed
}
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}
ch.readsem.wait()
}
if ch.cap > 0 {
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// try to get buffer token
mut obj_in_queue := false
mut rd_avail := C.atomic_load_u32(&ch.read_avail)
for rd_avail > 0 {
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obj_in_queue = C.atomic_compare_exchange_weak_u32(&ch.read_avail, &rd_avail,
rd_avail - 1)
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if obj_in_queue {
break
}
}
if obj_in_queue {
mut rd_idx := C.atomic_load_u32(&ch.buf_elem_read_idx)
for {
mut new_rd_idx := rd_idx + 1
for new_rd_idx >= ch.cap {
new_rd_idx -= ch.cap
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}
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if C.atomic_compare_exchange_weak_u32(&ch.buf_elem_read_idx, &rd_idx,
new_rd_idx)
{
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break
}
}
mut rd_ptr := ch.ringbuf
mut status_adr := ch.statusbuf
unsafe {
rd_ptr += rd_idx * ch.objsize
status_adr += rd_idx * sizeof(u16)
}
mut expected_status := u16(BufferElemStat.written)
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for !C.atomic_compare_exchange_weak_u16(unsafe { &u16(status_adr) },
&expected_status, u16(BufferElemStat.reading)) {
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expected_status = u16(BufferElemStat.written)
}
unsafe {
C.memcpy(dest, rd_ptr, ch.objsize)
}
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C.atomic_store_u16(unsafe { &u16(status_adr) }, u16(BufferElemStat.unused))
C.atomic_fetch_add_u32(&ch.write_free, 1)
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ch.writesem.post()
mut null16 := u16(0)
for !C.atomic_compare_exchange_weak_u16(&ch.write_sub_mtx, &null16, u16(1)) {
null16 = u16(0)
}
if ch.write_subscriber != voidptr(0) {
ch.write_subscriber.sem.post()
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}
C.atomic_store_u16(&ch.write_sub_mtx, u16(0))
return .success
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}
}
// try to advertise `dest` as writable
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C.atomic_store_ptr(unsafe { &voidptr(&ch.write_adr) }, dest)
if ch.cap == 0 {
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mut rdadr := C.atomic_load_ptr(unsafe { &voidptr(&ch.read_adr) })
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if rdadr != C.NULL {
mut dest2 := dest
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if C.atomic_compare_exchange_strong_ptr(unsafe { &voidptr(&ch.write_adr) },
&dest2, voidptr(0))
{
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ch.readsem.post()
continue
} else {
write_in_progress = true
}
}
}
if ch.cap == 0 && !write_in_progress {
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mut null16 := u16(0)
for !C.atomic_compare_exchange_weak_u16(&ch.write_sub_mtx, &null16, u16(1)) {
null16 = u16(0)
}
if ch.write_subscriber != voidptr(0) {
ch.write_subscriber.sem.post()
}
C.atomic_store_u16(&ch.write_sub_mtx, u16(0))
}
mut dest2 := dest
for sp := u32(0); sp < spinloops_ || write_in_progress; sp++ {
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if C.atomic_compare_exchange_strong_ptr(unsafe { &voidptr(&ch.adr_written) },
&dest2, voidptr(0))
{
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have_swapped = true
break
} else if dest2 == voidptr(-1) {
ch.readsem.post()
return .closed
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}
dest2 = dest
}
mut got_im_sem := false
for sp := u32(0); sp < spinloops_sem_ || write_in_progress; sp++ {
got_im_sem = ch.readsem_im.try_wait()
if got_im_sem {
break
}
}
for {
if got_im_sem {
got_im_sem = false
} else {
ch.readsem_im.wait()
}
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if have_swapped
|| C.atomic_compare_exchange_strong_ptr(unsafe { &voidptr(&ch.adr_written) }, &dest2, voidptr(0)) {
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ch.readsem.post()
break
} else {
// this semaphore was not for us - repost in
ch.readsem_im.post()
if dest2 == voidptr(-1) {
ch.readsem.post()
return .closed
}
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dest2 = dest
}
}
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break
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}
return .success
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}
// Wait `timeout` on any of `channels[i]` until one of them can push (`is_push[i] = true`) or pop (`is_push[i] = false`)
// object referenced by `objrefs[i]`. `timeout < 0` means wait unlimited time. `timeout == 0` means return immediately
// if no transaction can be performed without waiting.
// return value: the index of the channel on which a transaction has taken place
// -1 if waiting for a transaction has exceeded timeout
// -2 if all channels are closed
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pub fn channel_select(mut channels []&Channel, dir []Direction, mut objrefs []voidptr, timeout time.Duration) int {
assert channels.len == dir.len
assert dir.len == objrefs.len
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mut subscr := []Subscription{len: channels.len}
mut sem := unsafe { Semaphore{} }
sem.init(0)
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for i, ch in channels {
subscr[i].sem = &sem
if dir[i] == .push {
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mut null16 := u16(0)
for !C.atomic_compare_exchange_weak_u16(&ch.write_sub_mtx, &null16, u16(1)) {
null16 = u16(0)
}
subscr[i].prev = &ch.write_subscriber
unsafe {
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subscr[i].nxt = &Subscription(C.atomic_exchange_ptr(&voidptr(&ch.write_subscriber),
&subscr[i]))
}
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if voidptr(subscr[i].nxt) != voidptr(0) {
subscr[i].nxt.prev = &subscr[i].nxt
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}
C.atomic_store_u16(&ch.write_sub_mtx, u16(0))
} else {
mut null16 := u16(0)
for !C.atomic_compare_exchange_weak_u16(&ch.read_sub_mtx, &null16, u16(1)) {
null16 = u16(0)
}
subscr[i].prev = &ch.read_subscriber
unsafe {
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subscr[i].nxt = &Subscription(C.atomic_exchange_ptr(&voidptr(&ch.read_subscriber),
&subscr[i]))
}
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if voidptr(subscr[i].nxt) != voidptr(0) {
subscr[i].nxt.prev = &subscr[i].nxt
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}
C.atomic_store_u16(&ch.read_sub_mtx, u16(0))
}
}
stopwatch := if timeout <= 0 { time.StopWatch{} } else { time.new_stopwatch({}) }
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mut event_idx := -1 // negative index means `timed out`
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outer: for {
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rnd := rand.u32_in_range(0, u32(channels.len))
mut num_closed := 0
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for j, _ in channels {
mut i := j + int(rnd)
if i >= channels.len {
i -= channels.len
}
if dir[i] == .push {
stat := channels[i].try_push_priv(objrefs[i], true)
if stat == .success {
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event_idx = i
break outer
} else if stat == .closed {
num_closed++
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}
} else {
stat := channels[i].try_pop_priv(objrefs[i], true)
if stat == .success {
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event_idx = i
break outer
} else if stat == .closed {
num_closed++
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}
}
}
if num_closed == channels.len {
event_idx = -2
break outer
}
if timeout == 0 {
break outer
}
if timeout > 0 {
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remaining := timeout - stopwatch.elapsed()
if !sem.timed_wait(remaining) {
break outer
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}
} else {
sem.wait()
}
}
// reset subscribers
for i, ch in channels {
if dir[i] == .push {
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mut null16 := u16(0)
for !C.atomic_compare_exchange_weak_u16(&ch.write_sub_mtx, &null16, u16(1)) {
null16 = u16(0)
}
unsafe {
*subscr[i].prev = subscr[i].nxt
}
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if subscr[i].nxt != 0 {
subscr[i].nxt.prev = subscr[i].prev
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// just in case we have missed a semaphore during restore
subscr[i].nxt.sem.post()
}
C.atomic_store_u16(&ch.write_sub_mtx, u16(0))
} else {
mut null16 := u16(0)
for !C.atomic_compare_exchange_weak_u16(&ch.read_sub_mtx, &null16, u16(1)) {
null16 = u16(0)
}
unsafe {
*subscr[i].prev = subscr[i].nxt
}
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if subscr[i].nxt != 0 {
subscr[i].nxt.prev = subscr[i].prev
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subscr[i].nxt.sem.post()
}
C.atomic_store_u16(&ch.read_sub_mtx, u16(0))
}
}
sem.destroy()
return event_idx
}