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// Copyright (c) 2018 David Crawshaw <david@zentus.com>
// Copyright (c) 2021 Roxy Light <roxy@zombiezen.com>
//
// Permission to use, copy, modify, and distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
//
// SPDX-License-Identifier: ISC
package sqlite
import (
"fmt"
"sync"
"unsafe"
"modernc.org/libc"
"modernc.org/libc/sys/types"
lib "modernc.org/sqlite/lib"
)
// See https://sqlite.org/unlock_notify.html for detailed explanation.
// unlockNote is a C-allocated struct used as a condition variable.
type unlockNote struct {
mu sync.Mutex
wait sync.Mutex // held while fired == false
fired bool
}
func allocUnlockNote(tls *libc.TLS) (uintptr, error) {
ptr := libc.Xcalloc(tls, 1, types.Size_t(unsafe.Sizeof(unlockNote{})))
if ptr == 0 {
return 0, fmt.Errorf("out of memory for unlockNote")
}
un := (*unlockNote)(unsafe.Pointer(ptr))
un.wait.Lock()
return ptr, nil
}
func fireUnlockNote(tls *libc.TLS, ptr uintptr) {
un := (*unlockNote)(unsafe.Pointer(ptr))
un.mu.Lock()
if !un.fired {
un.fired = true
un.wait.Unlock()
}
un.mu.Unlock()
}
func unlockNotifyCallback(tls *libc.TLS, apArg uintptr, nArg int32) {
for ; nArg > 0; nArg-- {
fireUnlockNote(tls, *(*uintptr)(unsafe.Pointer(apArg)))
// apArg is a C array of pointers.
apArg += unsafe.Sizeof(uintptr(0))
}
}
func waitForUnlockNotify(tls *libc.TLS, db uintptr, unPtr uintptr) ResultCode {
un := (*unlockNote)(unsafe.Pointer(unPtr))
if un.fired {
un.wait.Lock()
}
un.fired = false
cbPtr := cFuncPointer(unlockNotifyCallback)
res := ResultCode(lib.Xsqlite3_unlock_notify(tls, db, cbPtr, unPtr))
if res == ResultOK {
un.mu.Lock()
fired := un.fired
un.mu.Unlock()
if !fired {
un.wait.Lock()
un.wait.Unlock()
}
}
return res
}
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