FilesExpand file tree

 master

/

OracleDbmsLock.cs

Copy path

Blame

More file actions

Blame

More file actions

Latest commit

 

History

History

History

134 lines (117 loc) · 5.63 KB

 master

/

OracleDbmsLock.cs

Copy path

Top

File metadata and controls

• Code
• Blame

134 lines (117 loc) · 5.63 KB

Raw

Copy raw file

Download raw file

Open symbols panel

Edit and raw actions

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

using Medallion.Threading.Internal;

using Medallion.Threading.Internal.Data;

using System.Data;

namespace Medallion.Threading.Oracle;

/// <summary>

/// Implements <see cref="IDbSynchronizationStrategy{TLockCookie}"/> using Oracle's DBMS_LOCK package

/// </summary>

internal class OracleDbmsLock : IDbSynchronizationStrategy<object>

{

// https://docs.oracle.com/cd/B19306_01/appdev.102/b14258/d_lock.htm#i1002309

private const int MaxWaitSeconds = 32767;

private const int MaxTimeoutSeconds = MaxWaitSeconds - 1;

public static readonly OracleDbmsLock SharedLock = new(Mode.Shared),

UpdateLock = new(Mode.Update),

ExclusiveLock = new(Mode.Exclusive),

UpgradeLock = new(Mode.Exclusive, isUpgrade: true);

private static readonly object Cookie = new();

private readonly Mode _mode;

private readonly bool _isUpgrade;

private OracleDbmsLock(Mode mode, bool isUpgrade = false)

{

Invariant.Require(!isUpgrade || mode == Mode.Exclusive);

this._mode = mode;

this._isUpgrade = isUpgrade;

}

public bool IsUpgradeable => this._mode == Mode.Update;

private string ModeSqlConstant

{

get

{

var modeCode = this._mode switch

{

Mode.Shared => "SS",

Mode.Update => "SSX",

Mode.Exclusive => "X",

_ => throw new InvalidOperationException(),

};

return $"SYS.DBMS_LOCK.{modeCode}_MODE";

}

}

public async ValueTask ReleaseAsync(DatabaseConnection connection, string resourceName, object lockCookie)

{

// Since we we don't allow downgrading and therefore "releasing" an upgrade only happens on disposal of the

// original handle, this can safely be a noop.

if (this._isUpgrade) { return; }

using var command = connection.CreateCommand();

command.SetCommandText(@"

DECLARE

lockHandle VARCHAR2(128);

BEGIN

SYS.DBMS_LOCK.ALLOCATE_UNIQUE(:lockName, lockHandle);

:returnValue := SYS.DBMS_LOCK.RELEASE(lockHandle);

END;"

);

// note: parameters bind by position by default!

command.AddParameter("lockName", resourceName);

var returnValueParameter = command.AddParameter("returnValue", type: DbType.Int32, direction: ParameterDirection.Output);

await command.ExecuteNonQueryAsync(CancellationToken.None).ConfigureAwait(false);

var returnValue = (int)returnValueParameter.Value;

if (returnValue != 0)

{

// we don't enumerate the error codes here because release shouldn't ever fail unless the user really messes things up

throw new InvalidOperationException($"SYS.DBMS_LOCK.RELEASE returned error code {returnValue}");

}

}

public async ValueTask<object?> TryAcquireAsync(DatabaseConnection connection, string resourceName, TimeoutValue timeout, CancellationToken cancellationToken)

{

var acquireFunction = this._isUpgrade ? "CONVERT" : "REQUEST";

using var command = connection.CreateCommand();

command.SetCommandText($@"

DECLARE

lockHandle VARCHAR2(128);

BEGIN

SYS.DBMS_LOCK.ALLOCATE_UNIQUE(:lockName, lockHandle);

:returnValue := SYS.DBMS_LOCK.{acquireFunction}(lockhandle => lockHandle, lockmode => {this.ModeSqlConstant}, timeout => :timeout);

END;"

);

// note: parameters bind by position by default!

command.AddParameter("lockName", resourceName);

var returnValueParameter = command.AddParameter("returnValue", type: DbType.Int32, direction: ParameterDirection.Output);

command.AddParameter(

"timeout",

timeout.IsInfinite ? MaxWaitSeconds

// we could support longer timeouts via looping lock requests, but this doesn't feel particularly valuable and isn't a true longer wait

// since by looping you fall out of the wait queue

: timeout.TimeSpan.TotalSeconds > MaxTimeoutSeconds ? throw new ArgumentOutOfRangeException($"Requested non-infinite timeout value '{timeout}' is longer than Oracle's allowed max of '{TimeSpan.FromSeconds(MaxTimeoutSeconds)}'")

: timeout.TimeSpan.TotalSeconds

);

await command.ExecuteNonQueryAsync(cancellationToken).ConfigureAwait(false);

var returnValue = (int)returnValueParameter.Value;

return returnValue switch

{

0 => Cookie, // success

1 => null, // timeout

2 => throw new DeadlockException(GetErrorMessage("deadlock")),

3 => throw new InvalidOperationException(GetErrorMessage("parameter error")),

4 => timeout.IsZero ? null

: timeout.IsInfinite ? throw new DeadlockException("Attempted to acquire a lock that is already held on the same connection")

: await WaitThenReturnNullAsync().ConfigureAwait(false),

5 => throw new InvalidOperationException(GetErrorMessage("illegal lock handle")),

_ => throw new InvalidOperationException(GetErrorMessage("unknown error code")),

};

string GetErrorMessage(string description) =>

$"SYS.DBMS_LOCK.{acquireFunction} returned error code {returnValue} ({description})";

async ValueTask<object?> WaitThenReturnNullAsync()

{

await SyncViaAsync.Delay(timeout, cancellationToken).ConfigureAwait(false);

return null;

}

}

private enum Mode

{

Shared,

Update,

Exclusive,

}

}