support SQLite's multi-thread model

1 files changed, 270 insertions, 0 deletions

diff --git a/mutex.go b/mutex.go
new file mode 100644
index 0000000..0bcc241
--- /dev/null
+++ b/mutex.go
@@ -0,0 +1,270 @@
+// Copyright 2019 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 sqlite // import "modernc.org/sqlite"
+
+import (
+	"sync"
+	"sync/atomic"
+	"unsafe"
+
+	"modernc.org/crt/v2"
+	"modernc.org/sqlite/internal/bin"
+)
+
+var (
+	mutexMethods = bin.Ssqlite3_mutex_methods{
+		FxMutexInit: *(*uintptr)(unsafe.Pointer(&struct{ f func(*crt.TLS) int32 }{mutexInit})),
+		FxMutexEnd:  *(*uintptr)(unsafe.Pointer(&struct{ f func(*crt.TLS) int32 }{mutexEnd})),
+		FxMutexAlloc: *(*uintptr)(unsafe.Pointer(&struct {
+			f func(*crt.TLS, int32) crt.Intptr
+		}{mutexAlloc})),
+		FxMutexFree:  *(*uintptr)(unsafe.Pointer(&struct{ f func(*crt.TLS, crt.Intptr) }{mutexFree})),
+		FxMutexEnter: *(*uintptr)(unsafe.Pointer(&struct{ f func(*crt.TLS, crt.Intptr) }{mutexEnter})),
+		FxMutexTry: *(*uintptr)(unsafe.Pointer(&struct {
+			f func(*crt.TLS, crt.Intptr) int32
+		}{mutexTry})),
+		FxMutexLeave: *(*uintptr)(unsafe.Pointer(&struct{ f func(*crt.TLS, crt.Intptr) }{mutexLeave})),
+		FxMutexHeld: *(*uintptr)(unsafe.Pointer(&struct {
+			f func(*crt.TLS, crt.Intptr) int32
+		}{mutexHeld})),
+		FxMutexNotheld: *(*uintptr)(unsafe.Pointer(&struct {
+			f func(*crt.TLS, crt.Intptr) int32
+		}{mutexNotheld})),
+	}
+
+	mutexApp1   mutex
+	mutexApp2   mutex
+	mutexApp3   mutex
+	mutexLRU    mutex
+	mutexMaster mutex
+	mutexMem    mutex
+	mutexOpen   mutex
+	mutexPMem   mutex
+	mutexPRNG   mutex
+	mutexVFS1   mutex
+	mutexVFS2   mutex
+	mutexVFS3   mutex
+)
+
+type mutex struct {
+	cnt int32
+	id  int32
+	sync.Mutex
+	wait sync.Mutex
+}
+
+func (m *mutex) enter(id int32) {
+	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
+		}
+
+		m.Unlock()
+		m.wait.Lock()
+		m.wait.Unlock()
+	}
+}
+
+func (m *mutex) leave() {
+	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 *crt.TLS) int32 { return bin.DSQLITE_OK }
+
+// int (*xMutexEnd)(void);
+func mutexEnd(tls *crt.TLS) int32 { return bin.DSQLITE_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 *crt.TLS, typ int32) (r crt.Intptr) {
+	defer func() {
+	}()
+	switch typ {
+	case
+		bin.DSQLITE_MUTEX_FAST,
+		bin.DSQLITE_MUTEX_RECURSIVE:
+
+		return crt.Xcalloc(tls, 1, crt.Intptr(unsafe.Sizeof(mutex{})))
+	case bin.DSQLITE_MUTEX_STATIC_MASTER:
+		return crt.Intptr(uintptr(unsafe.Pointer(&mutexMaster)))
+	case bin.DSQLITE_MUTEX_STATIC_MEM:
+		return crt.Intptr(uintptr(unsafe.Pointer(&mutexMem)))
+	case bin.DSQLITE_MUTEX_STATIC_OPEN:
+		return crt.Intptr(uintptr(unsafe.Pointer(&mutexOpen)))
+	case bin.DSQLITE_MUTEX_STATIC_PRNG:
+		return crt.Intptr(uintptr(unsafe.Pointer(&mutexPRNG)))
+	case bin.DSQLITE_MUTEX_STATIC_LRU:
+		return crt.Intptr(uintptr(unsafe.Pointer(&mutexLRU)))
+	case bin.DSQLITE_MUTEX_STATIC_PMEM:
+		return crt.Intptr(uintptr(unsafe.Pointer(&mutexPMem)))
+	case bin.DSQLITE_MUTEX_STATIC_APP1:
+		return crt.Intptr(uintptr(unsafe.Pointer(&mutexApp1)))
+	case bin.DSQLITE_MUTEX_STATIC_APP2:
+		return crt.Intptr(uintptr(unsafe.Pointer(&mutexApp2)))
+	case bin.DSQLITE_MUTEX_STATIC_APP3:
+		return crt.Intptr(uintptr(unsafe.Pointer(&mutexApp3)))
+	case bin.DSQLITE_MUTEX_STATIC_VFS1:
+		return crt.Intptr(uintptr(unsafe.Pointer(&mutexVFS1)))
+	case bin.DSQLITE_MUTEX_STATIC_VFS2:
+		return crt.Intptr(uintptr(unsafe.Pointer(&mutexVFS2)))
+	case bin.DSQLITE_MUTEX_STATIC_VFS3:
+		return crt.Intptr(uintptr(unsafe.Pointer(&mutexVFS3)))
+	default:
+		return 0
+	}
+}
+
+// void (*xMutexFree)(sqlite3_mutex *);
+func mutexFree(tls *crt.TLS, m crt.Intptr) { crt.Xfree(tls, 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 *crt.TLS, m crt.Intptr) {
+	if m == 0 {
+		return
+	}
+
+	(*mutex)(unsafe.Pointer(uintptr(m))).enter(tls.ID)
+}
+
+// int (*xMutexTry)(sqlite3_mutex *);
+func mutexTry(tls *crt.TLS, m crt.Intptr) int32 { return bin.DSQLITE_BUSY }
+
+// void (*xMutexLeave)(sqlite3_mutex *);
+func mutexLeave(tls *crt.TLS, m crt.Intptr) {
+	if m == 0 {
+		return
+	}
+
+	(*mutex)(unsafe.Pointer(uintptr(m))).leave()
+}
+
+// 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 *crt.TLS, m crt.Intptr) int32 {
+	if m == 0 {
+		return 1
+	}
+
+	return crt.Bool32(atomic.LoadInt32(&(*mutex)(unsafe.Pointer(uintptr(m))).id) == tls.ID)
+}
+
+// int (*xMutexNotheld)(sqlite3_mutex *);
+func mutexNotheld(tls *crt.TLS, m crt.Intptr) int32 {
+	if m == 0 {
+		return 1
+	}
+
+	return crt.Bool32(atomic.LoadInt32(&(*mutex)(unsafe.Pointer(uintptr(m))).id) != tls.ID)
+}