gotosocial/vendor/modernc.org/sqlite/lib/mutex.go

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// Copyright 2021 The Sqlite Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package sqlite3
import (
"fmt"
"sync"
"sync/atomic"
"unsafe"
"modernc.org/libc"
"modernc.org/libc/sys/types"
)
func init() {
tls := libc.NewTLS()
if Xsqlite3_threadsafe(tls) == 0 {
panic(fmt.Errorf("sqlite: thread safety configuration error"))
}
varArgs := libc.Xmalloc(tls, types.Size_t(unsafe.Sizeof(uintptr(0))))
if varArgs == 0 {
panic(fmt.Errorf("cannot allocate memory"))
}
// int sqlite3_config(int, ...);
if rc := Xsqlite3_config(tls, SQLITE_CONFIG_MUTEX, libc.VaList(varArgs, uintptr(unsafe.Pointer(&mutexMethods)))); rc != SQLITE_OK {
p := Xsqlite3_errstr(tls, rc)
str := libc.GoString(p)
panic(fmt.Errorf("sqlite: failed to configure mutex methods: %v", str))
}
libc.Xfree(tls, varArgs)
tls.Close()
}
var (
mutexMethods = Sqlite3_mutex_methods{
FxMutexInit: *(*uintptr)(unsafe.Pointer(&struct{ f func(*libc.TLS) int32 }{mutexInit})),
FxMutexEnd: *(*uintptr)(unsafe.Pointer(&struct{ f func(*libc.TLS) int32 }{mutexEnd})),
FxMutexAlloc: *(*uintptr)(unsafe.Pointer(&struct {
f func(*libc.TLS, int32) uintptr
}{mutexAlloc})),
FxMutexFree: *(*uintptr)(unsafe.Pointer(&struct{ f func(*libc.TLS, uintptr) }{mutexFree})),
FxMutexEnter: *(*uintptr)(unsafe.Pointer(&struct{ f func(*libc.TLS, uintptr) }{mutexEnter})),
FxMutexTry: *(*uintptr)(unsafe.Pointer(&struct {
f func(*libc.TLS, uintptr) int32
}{mutexTry})),
FxMutexLeave: *(*uintptr)(unsafe.Pointer(&struct{ f func(*libc.TLS, uintptr) }{mutexLeave})),
FxMutexHeld: *(*uintptr)(unsafe.Pointer(&struct {
f func(*libc.TLS, uintptr) int32
}{mutexHeld})),
FxMutexNotheld: *(*uintptr)(unsafe.Pointer(&struct {
f func(*libc.TLS, uintptr) int32
}{mutexNotheld})),
}
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MutexCounters = libc.NewPerfCounter([]string{
"enter-fast",
"enter-recursive",
"enter-recursive-loop",
"try-fast",
"try-recursive",
})
MutexEnterCallers = libc.NewStackCapture(4)
mutexes mutexPool
mutexApp1 = mutexes.alloc(false)
mutexApp2 = mutexes.alloc(false)
mutexApp3 = mutexes.alloc(false)
mutexLRU = mutexes.alloc(false)
mutexMaster = mutexes.alloc(false)
mutexMem = mutexes.alloc(false)
mutexOpen = mutexes.alloc(false)
mutexPMem = mutexes.alloc(false)
mutexPRNG = mutexes.alloc(false)
mutexVFS1 = mutexes.alloc(false)
mutexVFS2 = mutexes.alloc(false)
mutexVFS3 = mutexes.alloc(false)
)
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type mutexPool struct {
sync.Mutex
a []*[256]mutex
freeList []int
}
func mutexFromPtr(p uintptr) *mutex {
if p == 0 {
return nil
}
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ix := p - 1
mutexes.Lock()
defer mutexes.Unlock()
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return &mutexes.a[ix>>8][ix&255]
}
func (m *mutexPool) alloc(recursive bool) uintptr {
m.Lock()
defer m.Unlock()
n := len(m.freeList)
if n == 0 {
outer := len(m.a) << 8
m.a = append(m.a, &[256]mutex{})
for i := 0; i < 256; i++ {
m.freeList = append(m.freeList, outer+i)
}
n = len(m.freeList)
}
ix := m.freeList[n-1]
outer := ix >> 8
inner := ix & 255
m.freeList = m.freeList[:n-1]
p := &m.a[outer][inner]
p.poolIndex = ix
p.recursive = recursive
return uintptr(ix) + 1
}
func (m *mutexPool) free(p uintptr) {
ptr := mutexFromPtr(p)
ix := ptr.poolIndex
*ptr = mutex{}
m.Lock()
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defer m.Unlock()
m.freeList = append(m.freeList, ix)
}
type mutex struct {
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sync.Mutex
wait sync.Mutex
poolIndex int
cnt int32
id int32
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recursive bool
}
func (m *mutex) enter(id int32) {
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// MutexEnterCallers.Record()
if !m.recursive {
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// MutexCounters.Inc(0)
m.Lock()
m.id = id
return
}
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// MutexCounters.Inc(1)
for {
m.Lock()
switch m.id {
case 0:
m.cnt = 1
m.id = id
m.wait.Lock()
m.Unlock()
return
case id:
m.cnt++
m.Unlock()
return
}
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// MutexCounters.Inc(2)
m.Unlock()
m.wait.Lock()
//lint:ignore SA2001 TODO report staticcheck issue
m.wait.Unlock()
}
}
func (m *mutex) try(id int32) int32 {
if !m.recursive {
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// MutexCounters.Inc(3)
return SQLITE_BUSY
}
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// MutexCounters.Inc(4)
m.Lock()
switch m.id {
case 0:
m.cnt = 1
m.id = id
m.wait.Lock()
m.Unlock()
return SQLITE_OK
case id:
m.cnt++
m.Unlock()
return SQLITE_OK
}
m.Unlock()
return SQLITE_BUSY
}
func (m *mutex) leave(id int32) {
if !m.recursive {
m.id = 0
m.Unlock()
return
}
m.Lock()
m.cnt--
if m.cnt == 0 {
m.id = 0
m.wait.Unlock()
}
m.Unlock()
}
// int (*xMutexInit)(void);
//
// The xMutexInit method defined by this structure is invoked as part of system
// initialization by the sqlite3_initialize() function. The xMutexInit routine
// is called by SQLite exactly once for each effective call to
// sqlite3_initialize().
//
// The xMutexInit() method must be threadsafe. It must be harmless to invoke
// xMutexInit() multiple times within the same process and without intervening
// calls to xMutexEnd(). Second and subsequent calls to xMutexInit() must be
// no-ops. xMutexInit() must not use SQLite memory allocation (sqlite3_malloc()
// and its associates).
//
// If xMutexInit fails in any way, it is expected to clean up after itself
// prior to returning.
func mutexInit(tls *libc.TLS) int32 { return SQLITE_OK }
// int (*xMutexEnd)(void);
func mutexEnd(tls *libc.TLS) int32 { return SQLITE_OK }
// sqlite3_mutex *(*xMutexAlloc)(int);
//
// The sqlite3_mutex_alloc() routine allocates a new mutex and returns a
// pointer to it. The sqlite3_mutex_alloc() routine returns NULL if it is
// unable to allocate the requested mutex. The argument to
// sqlite3_mutex_alloc() must one of these integer constants:
//
// SQLITE_MUTEX_FAST
// SQLITE_MUTEX_RECURSIVE
// SQLITE_MUTEX_STATIC_MASTER
// SQLITE_MUTEX_STATIC_MEM
// SQLITE_MUTEX_STATIC_OPEN
// SQLITE_MUTEX_STATIC_PRNG
// SQLITE_MUTEX_STATIC_LRU
// SQLITE_MUTEX_STATIC_PMEM
// SQLITE_MUTEX_STATIC_APP1
// SQLITE_MUTEX_STATIC_APP2
// SQLITE_MUTEX_STATIC_APP3
// SQLITE_MUTEX_STATIC_VFS1
// SQLITE_MUTEX_STATIC_VFS2
// SQLITE_MUTEX_STATIC_VFS3
//
// The first two constants (SQLITE_MUTEX_FAST and SQLITE_MUTEX_RECURSIVE) cause
// sqlite3_mutex_alloc() to create a new mutex. The new mutex is recursive when
// SQLITE_MUTEX_RECURSIVE is used but not necessarily so when SQLITE_MUTEX_FAST
// is used. The mutex implementation does not need to make a distinction
// between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does not want to.
// SQLite will only request a recursive mutex in cases where it really needs
// one. If a faster non-recursive mutex implementation is available on the host
// platform, the mutex subsystem might return such a mutex in response to
// SQLITE_MUTEX_FAST.
//
// The other allowed parameters to sqlite3_mutex_alloc() (anything other than
// SQLITE_MUTEX_FAST and SQLITE_MUTEX_RECURSIVE) each return a pointer to a
// static preexisting mutex. Nine static mutexes are used by the current
// version of SQLite. Future versions of SQLite may add additional static
// mutexes. Static mutexes are for internal use by SQLite only. Applications
// that use SQLite mutexes should use only the dynamic mutexes returned by
// SQLITE_MUTEX_FAST or SQLITE_MUTEX_RECURSIVE.
//
// Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST or
// SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc() returns a
// different mutex on every call. For the static mutex types, the same mutex is
// returned on every call that has the same type number.
func mutexAlloc(tls *libc.TLS, typ int32) uintptr {
defer func() {
}()
switch typ {
case SQLITE_MUTEX_FAST:
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return mutexes.alloc(false)
case SQLITE_MUTEX_RECURSIVE:
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return mutexes.alloc(true)
case SQLITE_MUTEX_STATIC_MASTER:
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return mutexMaster
case SQLITE_MUTEX_STATIC_MEM:
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return mutexMem
case SQLITE_MUTEX_STATIC_OPEN:
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return mutexOpen
case SQLITE_MUTEX_STATIC_PRNG:
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return mutexPRNG
case SQLITE_MUTEX_STATIC_LRU:
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return mutexLRU
case SQLITE_MUTEX_STATIC_PMEM:
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return mutexPMem
case SQLITE_MUTEX_STATIC_APP1:
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return mutexApp1
case SQLITE_MUTEX_STATIC_APP2:
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return mutexApp2
case SQLITE_MUTEX_STATIC_APP3:
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return mutexApp3
case SQLITE_MUTEX_STATIC_VFS1:
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return mutexVFS1
case SQLITE_MUTEX_STATIC_VFS2:
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return mutexVFS2
case SQLITE_MUTEX_STATIC_VFS3:
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return mutexVFS3
default:
return 0
}
}
// void (*xMutexFree)(sqlite3_mutex *);
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func mutexFree(tls *libc.TLS, m uintptr) { mutexes.free(m) }
// The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt to enter
// a mutex. If another thread is already within the mutex,
// sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
// SQLITE_BUSY. The sqlite3_mutex_try() interface returns SQLITE_OK upon
// successful entry. Mutexes created using SQLITE_MUTEX_RECURSIVE can be
// entered multiple times by the same thread. In such cases, the mutex must be
// exited an equal number of times before another thread can enter. If the same
// thread tries to enter any mutex other than an SQLITE_MUTEX_RECURSIVE more
// than once, the behavior is undefined.
//
// If the argument to sqlite3_mutex_enter(), sqlite3_mutex_try(), or
// sqlite3_mutex_leave() is a NULL pointer, then all three routines behave as
// no-ops.
// void (*xMutexEnter)(sqlite3_mutex *);
func mutexEnter(tls *libc.TLS, m uintptr) {
if m == 0 {
return
}
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mutexFromPtr(m).enter(tls.ID)
}
// int (*xMutexTry)(sqlite3_mutex *);
func mutexTry(tls *libc.TLS, m uintptr) int32 {
if m == 0 {
return SQLITE_OK
}
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return mutexFromPtr(m).try(tls.ID)
}
// void (*xMutexLeave)(sqlite3_mutex *);
func mutexLeave(tls *libc.TLS, m uintptr) {
if m == 0 {
return
}
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mutexFromPtr(m).leave(tls.ID)
}
// The sqlite3_mutex_held() and sqlite3_mutex_notheld() routines are intended
// for use inside assert() statements. The SQLite core never uses these
// routines except inside an assert() and applications are advised to follow
// the lead of the core. The SQLite core only provides implementations for
// these routines when it is compiled with the SQLITE_DEBUG flag. External
// mutex implementations are only required to provide these routines if
// SQLITE_DEBUG is defined and if NDEBUG is not defined.
//
// These routines should return true if the mutex in their argument is held or
// not held, respectively, by the calling thread.
//
// The implementation is not required to provide versions of these routines
// that actually work. If the implementation does not provide working versions
// of these routines, it should at least provide stubs that always return true
// so that one does not get spurious assertion failures.
//
// If the argument to sqlite3_mutex_held() is a NULL pointer then the routine
// should return 1. This seems counter-intuitive since clearly the mutex cannot
// be held if it does not exist. But the reason the mutex does not exist is
// because the build is not using mutexes. And we do not want the assert()
// containing the call to sqlite3_mutex_held() to fail, so a non-zero return is
// the appropriate thing to do. The sqlite3_mutex_notheld() interface should
// also return 1 when given a NULL pointer.
// int (*xMutexHeld)(sqlite3_mutex *);
func mutexHeld(tls *libc.TLS, m uintptr) int32 {
if m == 0 {
return 1
}
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return libc.Bool32(atomic.LoadInt32(&mutexFromPtr(m).id) == tls.ID)
}
// int (*xMutexNotheld)(sqlite3_mutex *);
func mutexNotheld(tls *libc.TLS, m uintptr) int32 {
if m == 0 {
return 1
}
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return libc.Bool32(atomic.LoadInt32(&mutexFromPtr(m).id) != tls.ID)
}