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expression: fix data race of rand function #11168

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merged 3 commits into from
Jul 10, 2019
Merged

expression: fix data race of rand function #11168

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205bbe1
expressio: fix data race of rand function
alivxxx Jul 10, 2019
ebf1eea
refine test
alivxxx Jul 10, 2019
fe4b7be
Merge branch 'master' into data-race
alivxxx Jul 10, 2019
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13 changes: 9 additions & 4 deletions expression/builtin_math.go
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@ import (
"math/rand"
"strconv"
"strings"
"sync"
"time"

"github.com/cznic/mathutil"
Expand Down Expand Up @@ -966,7 +967,7 @@ func (c *randFunctionClass) getFunction(ctx sessionctx.Context, args []Expressio
bt := bf
if len(args) == 0 {
seed := time.Now().UnixNano()
sig = &builtinRandSig{bt, rand.New(rand.NewSource(seed))}
sig = &builtinRandSig{bt, &sync.Mutex{}, rand.New(rand.NewSource(seed))}
} else if _, isConstant := args[0].(*Constant); isConstant {
// According to MySQL manual:
// If an integer argument N is specified, it is used as the seed value:
Expand All @@ -979,7 +980,7 @@ func (c *randFunctionClass) getFunction(ctx sessionctx.Context, args []Expressio
if isNull {
seed = time.Now().UnixNano()
}
sig = &builtinRandSig{bt, rand.New(rand.NewSource(seed))}
sig = &builtinRandSig{bt, &sync.Mutex{}, rand.New(rand.NewSource(seed))}
} else {
sig = &builtinRandWithSeedSig{bt}
}
Expand All @@ -988,19 +989,23 @@ func (c *randFunctionClass) getFunction(ctx sessionctx.Context, args []Expressio

type builtinRandSig struct {
baseBuiltinFunc
mu *sync.Mutex
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All the projectWorkers will battle for this Mutex?

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Yes, and this is the only way to make it correct.

randGen *rand.Rand
}

func (b *builtinRandSig) Clone() builtinFunc {
newSig := &builtinRandSig{randGen: b.randGen}
newSig := &builtinRandSig{randGen: b.randGen, mu: b.mu}
newSig.cloneFrom(&b.baseBuiltinFunc)
return newSig
}

// evalReal evals RAND().
// See https://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html#function_rand
func (b *builtinRandSig) evalReal(row chunk.Row) (float64, bool, error) {
return b.randGen.Float64(), false, nil
b.mu.Lock()
res := b.randGen.Float64()
b.mu.Unlock()
return res, false, nil
}

type builtinRandWithSeedSig struct {
Expand Down
2 changes: 2 additions & 0 deletions expression/integration_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -551,6 +551,8 @@ func (s *testIntegrationSuite) TestMathBuiltin(c *C) {
tk.MustExec("drop table if exists t")
tk.MustExec("create table t(a int)")
tk.MustExec("insert into t values(1),(2),(3)")
tk.Se.GetSessionVars().MaxChunkSize = 1
tk.MustQuery("select rand(1) from t").Sort().Check(testkit.Rows("0.6046602879796196", "0.6645600532184904", "0.9405090880450124"))
tk.MustQuery("select rand(a) from t").Check(testkit.Rows("0.6046602879796196", "0.16729663442585624", "0.7199826688373036"))
tk.MustQuery("select rand(1), rand(2), rand(3)").Check(testkit.Rows("0.6046602879796196 0.16729663442585624 0.7199826688373036"))
}
Expand Down