source: code/trunk/vendor/modernc.org/sqlite/lib/mutex.go@ 822

// 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})),
        }

        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)
)

type mutexPool struct {
        sync.Mutex
        a        []*[256]mutex
        freeList []int
}

func mutexFromPtr(p uintptr) *mutex {
        if p == 0 {
                return nil
        }
        ix := p - 1
        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()

        defer m.Unlock()

        m.freeList = append(m.freeList, ix)
}

type mutex struct {
        sync.Mutex
        wait sync.Mutex

        poolIndex int

        cnt int32
        id  int32

        recursive bool
}

func (m *mutex) enter(id int32) {
        // MutexEnterCallers.Record()
        if !m.recursive {
                // MutexCounters.Inc(0)
                m.Lock()
                m.id = id
                return
        }

        // 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
                }

                // 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 {
                // MutexCounters.Inc(3)
                return SQLITE_BUSY
        }

        // 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:
                return mutexes.alloc(false)
        case SQLITE_MUTEX_RECURSIVE:
                return mutexes.alloc(true)
        case SQLITE_MUTEX_STATIC_MASTER:
                return mutexMaster
        case SQLITE_MUTEX_STATIC_MEM:
                return mutexMem
        case SQLITE_MUTEX_STATIC_OPEN:
                return mutexOpen
        case SQLITE_MUTEX_STATIC_PRNG:
                return mutexPRNG
        case SQLITE_MUTEX_STATIC_LRU:
                return mutexLRU
        case SQLITE_MUTEX_STATIC_PMEM:
                return mutexPMem
        case SQLITE_MUTEX_STATIC_APP1:
                return mutexApp1
        case SQLITE_MUTEX_STATIC_APP2:
                return mutexApp2
        case SQLITE_MUTEX_STATIC_APP3:
                return mutexApp3
        case SQLITE_MUTEX_STATIC_VFS1:
                return mutexVFS1
        case SQLITE_MUTEX_STATIC_VFS2:
                return mutexVFS2
        case SQLITE_MUTEX_STATIC_VFS3:
                return mutexVFS3
        default:
                return 0
        }
}

// void (*xMutexFree)(sqlite3_mutex *);
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
        }
        mutexFromPtr(m).enter(tls.ID)
}

// int (*xMutexTry)(sqlite3_mutex *);
func mutexTry(tls *libc.TLS, m uintptr) int32 {
        if m == 0 {
                return SQLITE_OK
        }

        return mutexFromPtr(m).try(tls.ID)
}

// void (*xMutexLeave)(sqlite3_mutex *);
func mutexLeave(tls *libc.TLS, m uintptr) {
        if m == 0 {
                return
        }

        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
        }

        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
        }

        return libc.Bool32(atomic.LoadInt32(&mutexFromPtr(m).id) != tls.ID)
}