C# - lock Keyword - Dot Net Perls

Lock. This C# keyword is used in threading. It restricts code from being executed by more than one thread at the same time. This makes threaded programs reliable.

The lock statement uses a special syntax form to restrict concurrent access. Lock is compiled into a lower-level implementation based on threading primitives.

An example. The Main method creates 10 new threads, and then calls Start on each one. Please examine method "A" to see the lock statement.

Detail This uses lock on an object. Each invocation of this method accesses the threading primitives implemented by the lock.

Then Only one method A can call the statements protected by the lock at a single time, regardless of the thread count.

Info Method A is invoked 10 times. The output shows the protected method region is executed sequentially—about 100 milliseconds apart.

ThreadStart

Thread.Sleep

Note If you remove the lock statement, the methods will be executed all at once, with no synchronization.

static

using System; using System.Threading; class Program { static readonly object _object = new object(); static void A() { // Method A: lock on the readonly object. // ... Inside the lock, sleep for 100 milliseconds. // ... This is thread serialization. lock (_object) { Thread.Sleep(100); Console.WriteLine(Environment.TickCount); } } static void Main() { // Create 10 new threads. for (int i = 0; i < 10; i++) { ThreadStart start = new ThreadStart(A); new Thread(start).Start(); } } }

28106840 28106949 28107043 28107136 28107246 28107339 28107448 28107542 28107636 28107745

IL. Let's examine the intermediate representation for the lock statement. In compiler theory, high-level source texts are translated to lower-level streams of instructions.

Intermediate Language

Tip The lock statement here is transformed into calls to the static methods Monitor.Enter and Monitor.Exit.

Also The lock is actually implemented with a try-finally construct. This uses the exception handling control flow.

try

finally

.method private hidebysig static void A() cil managed { .maxstack 2 .locals init ( [0] object obj2) L_0000: ldsfld object Program::_object L_0005: dup L_0006: stloc.0 L_0007: call void [mscorlib]System.Threading.Monitor::Enter(object) L_000c: ldc.i4.s 100 L_000e: call void [mscorlib]System.Threading.Thread::Sleep(int32) L_0013: call int32 [mscorlib]System.Environment::get_TickCount() L_0018: call void [mscorlib]System.Console::WriteLine(int32) L_001d: leave.s L_0026 L_001f: ldloc.0 L_0020: call void [mscorlib]System.Threading.Monitor::Exit(object) L_0025: endfinally L_0026: ret .try L_000c to L_001f finally handler L_001f to L_0026 }

A summary. Lock is a synchronization construct. We looked at an example and stepped into the IL. This keyword is helpful for threaded programs.