Monitor.TryEnter Método
Definição
Tenta adquirir um bloqueio exclusivo no objeto especificado.Attempts to acquire an exclusive lock on the specified object.
Sobrecargas
| TryEnter(Object, TimeSpan, Boolean) |
Tenta, pelo período especificado, obter um bloqueio exclusivo no objeto especificado e define automaticamente um valor que indica se o bloqueio foi realizado.Attempts, for the specified amount of time, to acquire an exclusive lock on the specified object, and atomically sets a value that indicates whether the lock was taken. |
| TryEnter(Object, Int32, Boolean) |
Tenta, pelo número de milissegundos especificado, obter um bloqueio exclusivo no objeto especificado e define de forma atômica um valor que indica se o bloqueio foi realizado.Attempts, for the specified number of milliseconds, to acquire an exclusive lock on the specified object, and atomically sets a value that indicates whether the lock was taken. |
| TryEnter(Object, TimeSpan) |
Tentativas, durante o período especificado de tempo, para adquirir um bloqueio exclusivo no objeto especificado.Attempts, for the specified amount of time, to acquire an exclusive lock on the specified object. |
| TryEnter(Object, Boolean) |
Tenta obter um bloqueio exclusivo no objeto especificado e define automaticamente um valor que indica se o bloqueio foi realizado.Attempts to acquire an exclusive lock on the specified object, and atomically sets a value that indicates whether the lock was taken. |
| TryEnter(Object) |
Tenta adquirir um bloqueio exclusivo no objeto especificado.Attempts to acquire an exclusive lock on the specified object. |
| TryEnter(Object, Int32) |
Tentativas, durante o período especificado de milésimos de segundos, para adquirir um bloqueio exclusivo no objeto especificado.Attempts, for the specified number of milliseconds, to acquire an exclusive lock on the specified object. |
TryEnter(Object, TimeSpan, Boolean)
Tenta, pelo período especificado, obter um bloqueio exclusivo no objeto especificado e define automaticamente um valor que indica se o bloqueio foi realizado.Attempts, for the specified amount of time, to acquire an exclusive lock on the specified object, and atomically sets a value that indicates whether the lock was taken.
public:
static void TryEnter(System::Object ^ obj, TimeSpan timeout, bool % lockTaken);
public static void TryEnter (object obj, TimeSpan timeout, ref bool lockTaken);
static member TryEnter : obj * TimeSpan * bool -> unit
Public Shared Sub TryEnter (obj As Object, timeout As TimeSpan, ByRef lockTaken As Boolean)
Parâmetros
- obj
- Object
O objeto no qual adquirir o bloqueio.The object on which to acquire the lock.
- timeout
- TimeSpan
A quantidade de tempo a esperar pelo bloqueio.The amount of time to wait for the lock. Um valor de -1 milissegundo especifica uma espera infinita.A value of -1 millisecond specifies an infinite wait.
- lockTaken
- Boolean
O resultado da tentativa de adquirir o bloqueio, passado por referência.The result of the attempt to acquire the lock, passed by reference. A entrada deve ser false.The input must be false. A saída será true se o bloqueio for adquirido; caso contrário, a saída será false.The output is true if the lock is acquired; otherwise, the output is false. A saída é definida mesmo se ocorrer uma exceção durante a tentativa de adquirir o bloqueio.The output is set even if an exception occurs during the attempt to acquire the lock.
Exceções
A entrada para lockTaken é true.The input to lockTaken is true.
O parâmetro obj é null.The obj parameter is null.
O valor de timeout em milissegundos é negativo e não é igual a Infinite (-1 milissegundo) ou é maior que MaxValue.The value of timeout in milliseconds is negative and is not equal to Infinite (-1 millisecond), or is greater than MaxValue.
Comentários
Se o valor do timeout parâmetro convertido em milissegundos for igual a-1, esse método será equivalente a Enter(Object) .If the value of the timeout parameter converted to milliseconds equals -1, this method is equivalent to Enter(Object). Se o valor timeout igual a 0, esse método é equivalente a TryEnter(Object) .If the value of timeout equals 0, this method is equivalent to TryEnter(Object).
Se o bloqueio não foi feito porque uma exceção foi gerada, a variável especificada para o lockTaken parâmetro é false depois que esse método termina.If the lock was not taken because an exception was thrown, the variable specified for the lockTaken parameter is false after this method ends. Isso permite que o programa determine, em todos os casos, se é necessário liberar o bloqueio.This allows the program to determine, in all cases, whether it is necessary to release the lock.
Observação
Use Monitor para bloquear objetos (ou seja, tipos de referência), não tipos de valor.Use Monitor to lock objects (that is, reference types), not value types. Para obter mais informações, consulte o Monitor tópico classe.For more information, see the Monitor class topic.
Para garantir que o thread não insira a seção crítica, você deve examinar o valor de lockTaken e executar o código na seção crítica somente se seu valor for true .To ensure that the thread does not enter the critical section, you should examine the value of lockTaken and execute code in the critical section only if its value is true. O fragmento de código a seguir mostra o padrão usado para chamar esse método.The following code fragment shows the pattern used to call this method. Observe que você deve chamar Exit em um finally bloco para garantir que o thread de chamada libere seu bloqueio na seção crítica se ocorrer uma exceção.Note that you should call Exit in a finally block to ensure that the calling thread releases its lock on the critical section if an exception occurs.
var lockObj = new Object();
var timeout = TimeSpan.FromMilliseconds(500);
bool lockTaken = false;
try {
Monitor.TryEnter(lockObj, timeout, ref lockTaken);
if (lockTaken) {
// The critical section.
}
else {
// The lock was not acquired.
}
}
finally {
// Ensure that the lock is released.
if (lockTaken) {
Monitor.Exit(lockObj);
}
}
Dim lockObj As New Object()
Dim timeout = TimeSpan.FromMilliseconds(500)
Dim lockTaken As Boolean = False
Try
Monitor.TryEnter(lockObj, timeout, lockTaken)
If lockTaken Then
' The critical section.
Else
' The lock was not acquired.
End If
Finally
' Ensure that the lock is released.
If lockTaken Then Monitor.Exit(lockObj)
End Try
Confira também
Aplica-se a
TryEnter(Object, Int32, Boolean)
Tenta, pelo número de milissegundos especificado, obter um bloqueio exclusivo no objeto especificado e define de forma atômica um valor que indica se o bloqueio foi realizado.Attempts, for the specified number of milliseconds, to acquire an exclusive lock on the specified object, and atomically sets a value that indicates whether the lock was taken.
public:
static void TryEnter(System::Object ^ obj, int millisecondsTimeout, bool % lockTaken);
public static void TryEnter (object obj, int millisecondsTimeout, ref bool lockTaken);
static member TryEnter : obj * int * bool -> unit
Public Shared Sub TryEnter (obj As Object, millisecondsTimeout As Integer, ByRef lockTaken As Boolean)
Parâmetros
- obj
- Object
O objeto no qual adquirir o bloqueio.The object on which to acquire the lock.
- millisecondsTimeout
- Int32
O número de milésimos de segundos de espera do bloqueio.The number of milliseconds to wait for the lock.
- lockTaken
- Boolean
O resultado da tentativa de adquirir o bloqueio, passado por referência.The result of the attempt to acquire the lock, passed by reference. A entrada deve ser false.The input must be false. A saída será true se o bloqueio for adquirido; caso contrário, a saída será false.The output is true if the lock is acquired; otherwise, the output is false. A saída é definida mesmo se ocorrer uma exceção durante a tentativa de adquirir o bloqueio.The output is set even if an exception occurs during the attempt to acquire the lock.
Exceções
A entrada para lockTaken é true.The input to lockTaken is true.
O parâmetro obj é null.The obj parameter is null.
millisecondsTimeout é negativo e diferente de Infinite.millisecondsTimeout is negative, and not equal to Infinite.
Exemplos
O código a seguir mostra o padrão básico para usar a TryEnter(Object, Boolean) sobrecarga do método.The following code shows the basic pattern for using the TryEnter(Object, Boolean) method overload. Essa sobrecarga sempre define o valor da variável que é passada para o ref parâmetro ( ByRef em Visual Basic) lockTaken , mesmo que o método gere uma exceção, de modo que o valor da variável é uma maneira confiável de testar se o bloqueio deve ser liberado.This overload always sets the value of the variable that is passed to the ref parameter (ByRef in Visual Basic) lockTaken, even if the method throws an exception, so the value of the variable is a reliable way to test whether the lock has to be released.
bool acquiredLock = false;
try
{
Monitor.TryEnter(lockObject, 500, ref acquiredLock);
if (acquiredLock)
{
// Code that accesses resources that are protected by the lock.
}
else
{
// Code to deal with the fact that the lock was not acquired.
}
}
finally
{
if (acquiredLock)
{
Monitor.Exit(lockObject);
}
}
Dim acquiredLock As Boolean = False
Try
Monitor.TryEnter(lockObject, 500, acquiredLock)
If acquiredLock Then
' Code that accesses resources that are protected by the lock.
Else
' Code to deal with the fact that the lock was not acquired.
End If
Finally
If acquiredLock Then
Monitor.Exit(lockObject)
End If
End Try
Comentários
Se o millisecondsTimeout parâmetro for igual a Infinite , esse método será equivalente a Enter(Object) .If the millisecondsTimeout parameter equals Infinite, this method is equivalent to Enter(Object). Se for millisecondsTimeout igual a 0, esse método será equivalente a TryEnter(Object) .If millisecondsTimeout equals 0, this method is equivalent to TryEnter(Object).
Se o bloqueio não foi feito porque uma exceção foi gerada, a variável especificada para o lockTaken parâmetro é false depois que esse método termina.If the lock was not taken because an exception was thrown, the variable specified for the lockTaken parameter is false after this method ends. Isso permite que o programa determine, em todos os casos, se é necessário liberar o bloqueio.This allows the program to determine, in all cases, whether it is necessary to release the lock.
Observação
Use Monitor para bloquear objetos (ou seja, tipos de referência), não tipos de valor.Use Monitor to lock objects (that is, reference types), not value types. Para obter mais informações, consulte o Monitor tópico classe.For more information, see the Monitor class topic.
Para garantir que o thread não insira a seção crítica, você deve examinar o valor de lockTaken e executar o código na seção crítica somente se seu valor for true .To ensure that the thread does not enter the critical section, you should examine the value of lockTaken and execute code in the critical section only if its value is true. O fragmento de código a seguir mostra o padrão usado para chamar esse método.The following code fragment shows the pattern used to call this method. Observe que você deve chamar Exit em um finally bloco para garantir que o thread de chamada libere seu bloqueio na seção crítica se ocorrer uma exceção.Note that you should call Exit in a finally block to ensure that the calling thread releases its lock on the critical section if an exception occurs.
var lockObj = new Object();
int timeout = 500;
bool lockTaken = false;
try {
Monitor.TryEnter(lockObj, timeout, ref lockTaken);
if (lockTaken) {
// The critical section.
}
else {
// The lock was not acquired.
}
}
finally {
// Ensure that the lock is released.
if (lockTaken) {
Monitor.Exit(lockObj);
}
}
Dim lockObj As New Object()
Dim timeout As Integer = 500
Dim lockTaken As Boolean = False
Try
Monitor.TryEnter(lockObj, timeout, lockTaken)
If lockTaken Then
' The critical section.
Else
' The lock was not acquired.
End If
Finally
' Ensure that the lock is released.
If lockTaken Then Monitor.Exit(lockObj)
End Try
Aplica-se a
TryEnter(Object, TimeSpan)
Tentativas, durante o período especificado de tempo, para adquirir um bloqueio exclusivo no objeto especificado.Attempts, for the specified amount of time, to acquire an exclusive lock on the specified object.
public:
static bool TryEnter(System::Object ^ obj, TimeSpan timeout);
public static bool TryEnter (object obj, TimeSpan timeout);
static member TryEnter : obj * TimeSpan -> bool
Public Shared Function TryEnter (obj As Object, timeout As TimeSpan) As Boolean
Parâmetros
- obj
- Object
O objeto no qual adquirir o bloqueio.The object on which to acquire the lock.
- timeout
- TimeSpan
Um TimeSpan que representa a quantidade de tempo a esperar pelo bloqueio.A TimeSpan representing the amount of time to wait for the lock. Um valor de -1 milissegundo especifica uma espera infinita.A value of -1 millisecond specifies an infinite wait.
Retornos
true se o thread atual adquirir o bloqueio; caso contrário, false.true if the current thread acquires the lock; otherwise, false.
Exceções
O parâmetro obj é null.The obj parameter is null.
O valor de timeout em milissegundos é negativo e não é igual a Infinite (-1 milissegundo) ou é maior que MaxValue.The value of timeout in milliseconds is negative and is not equal to Infinite (-1 millisecond), or is greater than MaxValue.
Comentários
Se o valor do timeout parâmetro convertido em milissegundos for igual a-1, esse método será equivalente a Enter .If the value of the timeout parameter converted to milliseconds equals -1, this method is equivalent to Enter. Se o valor timeout igual a 0, esse método é equivalente a TryEnter .If the value of timeout equals 0, this method is equivalent to TryEnter.
Observação
Use Monitor para bloquear objetos (ou seja, tipos de referência), não tipos de valor.Use Monitor to lock objects (that is, reference types), not value types. Para obter detalhes, consulte o Monitor tópico classe.For details, see the Monitor class topic.
Para garantir que o thread não insira a seção crítica, você deve examinar o valor de retorno do método e executar o código na seção crítica somente se o valor de retorno for true .To ensure that the thread does not enter the critical section, you should examine the method's return value and execute code in the critical section only if its return value is true. O fragmento de código a seguir mostra o padrão usado para chamar esse método.The following code fragment shows the pattern used to call this method. Observe que você deve chamar Exit em um finally bloco para garantir que o thread de chamada libere seu bloqueio na seção crítica se ocorrer uma exceção.Note that you should call Exit in a finally block to ensure that the calling thread releases its lock on the critical section if an exception occurs.
var lockObj = new Object();
var timeout = TimeSpan.FromMilliseconds(500);
if (Monitor.TryEnter(lockObj, timeout)) {
try {
// The critical section.
}
finally {
// Ensure that the lock is released.
Monitor.Exit(lockObj);
}
}
else {
// The lock was not acquired.
}
Dim lockObj As New Object()
Dim timeout = TimeSpan.FromMilliseconds(500)
If Monitor.TryEnter(lockObj, timeout) Then
Try
' The critical section.
Finally
' Ensure that the lock is released.
Monitor.Exit(lockObj)
End Try
Else
' The lock was not acquired.
End If
Confira também
Aplica-se a
TryEnter(Object, Boolean)
Tenta obter um bloqueio exclusivo no objeto especificado e define automaticamente um valor que indica se o bloqueio foi realizado.Attempts to acquire an exclusive lock on the specified object, and atomically sets a value that indicates whether the lock was taken.
public:
static void TryEnter(System::Object ^ obj, bool % lockTaken);
public static void TryEnter (object obj, ref bool lockTaken);
static member TryEnter : obj * bool -> unit
Public Shared Sub TryEnter (obj As Object, ByRef lockTaken As Boolean)
Parâmetros
- obj
- Object
O objeto no qual adquirir o bloqueio.The object on which to acquire the lock.
- lockTaken
- Boolean
O resultado da tentativa de adquirir o bloqueio, passado por referência.The result of the attempt to acquire the lock, passed by reference. A entrada deve ser false.The input must be false. A saída será true se o bloqueio for adquirido; caso contrário, a saída será false.The output is true if the lock is acquired; otherwise, the output is false. A saída é definida mesmo se ocorrer uma exceção durante a tentativa de adquirir o bloqueio.The output is set even if an exception occurs during the attempt to acquire the lock.
Exceções
A entrada para lockTaken é true.The input to lockTaken is true.
O parâmetro obj é null.The obj parameter is null.
Exemplos
O código a seguir mostra o padrão básico para usar a TryEnter(Object, Boolean) sobrecarga do método.The following code shows the basic pattern for using the TryEnter(Object, Boolean) method overload. Essa sobrecarga sempre define o valor da variável que é passada para o ref parâmetro ( ByRef em Visual Basic) lockTaken , mesmo que o método gere uma exceção, de modo que o valor da variável é uma maneira confiável de testar se o bloqueio deve ser liberado.This overload always sets the value of the variable that is passed to the ref parameter (ByRef in Visual Basic) lockTaken, even if the method throws an exception, so the value of the variable is a reliable way to test whether the lock has to be released.
bool acquiredLock = false;
try
{
Monitor.TryEnter(lockObject, ref acquiredLock);
if (acquiredLock)
{
// Code that accesses resources that are protected by the lock.
}
else
{
// Code to deal with the fact that the lock was not acquired.
}
}
finally
{
if (acquiredLock)
{
Monitor.Exit(lockObject);
}
}
Dim acquiredLock As Boolean = False
Try
Monitor.TryEnter(lockObject, acquiredLock)
If acquiredLock Then
' Code that accesses resources that are protected by the lock.
Else
' Code to deal with the fact that the lock was not acquired.
End If
Finally
If acquiredLock Then
Monitor.Exit(lockObject)
End If
End Try
Comentários
Se for bem-sucedido, esse método adquire um bloqueio exclusivo no obj parâmetro.If successful, this method acquires an exclusive lock on the obj parameter. Esse método retorna imediatamente, independentemente de o bloqueio estar ou não disponível.This method returns immediately, whether or not the lock is available.
Se o bloqueio não foi feito porque uma exceção foi gerada, a variável especificada para o lockTaken parâmetro é false depois que esse método termina.If the lock was not taken because an exception was thrown, the variable specified for the lockTaken parameter is false after this method ends. Isso permite que o programa determine, em todos os casos, se é necessário liberar o bloqueio.This allows the program to determine, in all cases, whether it is necessary to release the lock.
Esse método é semelhante a Enter(Object, Boolean) , mas nunca bloqueará o thread atual.This method is similar to Enter(Object, Boolean), but it will never block the current thread. Se o thread não puder entrar sem bloqueio, o lockTaken argumento será definido como false quando o método retornar.If the thread cannot enter without blocking, the lockTaken argument is set to false when the method returns.
Observação
Use Monitor para bloquear objetos (ou seja, tipos de referência), não tipos de valor.Use Monitor to lock objects (that is, reference types), not value types. Para obter mais informações, consulte o Monitor artigo.For more information, see the Monitor article.
Para garantir que o thread não insira a seção crítica, você deve examinar o valor de lockTaken e executar o código na seção crítica somente se seu valor for true .To ensure that the thread does not enter the critical section, you should examine the value of lockTaken and execute code in the critical section only if its value is true. O fragmento de código a seguir mostra o padrão usado para chamar esse método.The following code fragment shows the pattern used to call this method. Observe que você deve chamar Exit em um finally bloco para garantir que o thread de chamada libere seu bloqueio na seção crítica se ocorrer uma exceção.Note that you should call Exit in a finally block to ensure that the calling thread releases its lock on the critical section if an exception occurs.
var lockObj = new Object();
bool lockTaken = false;
try {
Monitor.TryEnter(lockObj, ref lockTaken);
if (lockTaken) {
// The critical section.
}
else {
// The lock was not acquired.
}
}
finally {
// Ensure that the lock is released.
if (lockTaken) {
Monitor.Exit(lockObj);
}
}
Dim lockObj As New Object()
Dim lockTaken As Boolean = False
Try
Monitor.TryEnter(lockObj, lockTaken)
If lockTaken Then
' The critical section.
Else
' The lock was not acquired.
End If
Finally
' Ensure that the lock is released.
If lockTaken Then Monitor.Exit(lockObj)
End Try
Aplica-se a
TryEnter(Object)
Tenta adquirir um bloqueio exclusivo no objeto especificado.Attempts to acquire an exclusive lock on the specified object.
public:
static bool TryEnter(System::Object ^ obj);
public static bool TryEnter (object obj);
static member TryEnter : obj -> bool
Public Shared Function TryEnter (obj As Object) As Boolean
Parâmetros
- obj
- Object
O objeto no qual adquirir o bloqueio.The object on which to acquire the lock.
Retornos
true se o thread atual adquirir o bloqueio; caso contrário, false.true if the current thread acquires the lock; otherwise, false.
Exceções
O parâmetro obj é null.The obj parameter is null.
Exemplos
O exemplo de código a seguir demonstra como usar o TryEnter método.The following code example demonstrates how to use the TryEnter method.
#using <System.dll>
using namespace System;
using namespace System::Threading;
using namespace System::Collections::Generic;
using namespace System::Text;
generic <typename T> public ref class SafeQueue
{
private:
// A queue that is protected by Monitor.
Queue<T>^ m_inputQueue;
public:
SafeQueue()
{
m_inputQueue = gcnew Queue<T>();
};
// Lock the queue and add an element.
void Enqueue(T qValue)
{
// Request the lock, and block until it is obtained.
Monitor::Enter(m_inputQueue);
try
{
// When the lock is obtained, add an element.
m_inputQueue->Enqueue(qValue);
}
finally
{
// Ensure that the lock is released.
Monitor::Exit(m_inputQueue);
}
};
// Try to add an element to the queue: Add the element to the queue
// only if the lock is immediately available.
bool TryEnqueue(T qValue)
{
// Request the lock.
if (Monitor::TryEnter(m_inputQueue))
{
try
{
m_inputQueue->Enqueue(qValue);
}
finally
{
// Ensure that the lock is released.
Monitor::Exit(m_inputQueue);
}
return true;
}
else
{
return false;
}
};
// Try to add an element to the queue: Add the element to the queue
// only if the lock becomes available during the specified time
// interval.
bool TryEnqueue(T qValue, int waitTime)
{
// Request the lock.
if (Monitor::TryEnter(m_inputQueue, waitTime))
{
try
{
m_inputQueue->Enqueue(qValue);
}
finally
{
// Ensure that the lock is released.
Monitor::Exit(m_inputQueue);
}
return true;
}
else
{
return false;
}
};
// Lock the queue and dequeue an element.
T Dequeue()
{
T retval;
// Request the lock, and block until it is obtained.
Monitor::Enter(m_inputQueue);
try
{
// When the lock is obtained, dequeue an element.
retval = m_inputQueue->Dequeue();
}
finally
{
// Ensure that the lock is released.
Monitor::Exit(m_inputQueue);
}
return retval;
};
// Delete all elements that equal the given object.
int Remove(T qValue)
{
int removedCt = 0;
// Wait until the lock is available and lock the queue.
Monitor::Enter(m_inputQueue);
try
{
int counter = m_inputQueue->Count;
while (counter > 0)
// Check each element.
{
T elem = m_inputQueue->Dequeue();
if (!elem->Equals(qValue))
{
m_inputQueue->Enqueue(elem);
}
else
{
// Keep a count of items removed.
removedCt += 1;
}
counter = counter - 1;
}
}
finally
{
// Ensure that the lock is released.
Monitor::Exit(m_inputQueue);
}
return removedCt;
};
// Print all queue elements.
String^ PrintAllElements()
{
StringBuilder^ output = gcnew StringBuilder();
// Lock the queue.
Monitor::Enter(m_inputQueue);
try
{
for each ( T elem in m_inputQueue )
{
// Print the next element.
output->AppendLine(elem->ToString());
}
}
finally
{
// Ensure that the lock is released.
Monitor::Exit(m_inputQueue);
}
return output->ToString();
};
};
public ref class Example
{
private:
static SafeQueue<int>^ q = gcnew SafeQueue<int>();
static int threadsRunning = 0;
static array<array<int>^>^ results = gcnew array<array<int>^>(3);
static void ThreadProc(Object^ state)
{
DateTime finish = DateTime::Now.AddSeconds(10);
Random^ rand = gcnew Random();
array<int>^ result = { 0, 0, 0, 0, 0, 0, 0, 0, 0 };
int threadNum = (int) state;
while (DateTime::Now < finish)
{
int what = rand->Next(250);
int how = rand->Next(100);
if (how < 16)
{
q->Enqueue(what);
result[(int)ThreadResultIndex::EnqueueCt] += 1;
}
else if (how < 32)
{
if (q->TryEnqueue(what))
{
result[(int)ThreadResultIndex::TryEnqueueSucceedCt] += 1;
}
else
{
result[(int)ThreadResultIndex::TryEnqueueFailCt] += 1;
}
}
else if (how < 48)
{
// Even a very small wait significantly increases the success
// rate of the conditional enqueue operation.
if (q->TryEnqueue(what, 10))
{
result[(int)ThreadResultIndex::TryEnqueueWaitSucceedCt] += 1;
}
else
{
result[(int)ThreadResultIndex::TryEnqueueWaitFailCt] += 1;
}
}
else if (how < 96)
{
result[(int)ThreadResultIndex::DequeueCt] += 1;
try
{
q->Dequeue();
}
catch (Exception^ ex)
{
result[(int)ThreadResultIndex::DequeueExCt] += 1;
}
}
else
{
result[(int)ThreadResultIndex::RemoveCt] += 1;
result[(int)ThreadResultIndex::RemovedCt] += q->Remove(what);
}
}
results[threadNum] = result;
if (0 == Interlocked::Decrement(threadsRunning))
{
StringBuilder^ sb = gcnew StringBuilder(
" Thread 1 Thread 2 Thread 3 Total\n");
for (int row = 0; row < 9; row++)
{
int total = 0;
sb->Append(titles[row]);
for(int col = 0; col < 3; col++)
{
sb->Append(String::Format("{0,9}", results[col][row]));
total += results[col][row];
}
sb->AppendLine(String::Format("{0,9}", total));
}
Console::WriteLine(sb->ToString());
}
};
static array<String^>^ titles = {
"Enqueue ",
"TryEnqueue succeeded ",
"TryEnqueue failed ",
"TryEnqueue(T, wait) succeeded ",
"TryEnqueue(T, wait) failed ",
"Dequeue attempts ",
"Dequeue exceptions ",
"Remove operations ",
"Queue elements removed "};
enum class ThreadResultIndex
{
EnqueueCt,
TryEnqueueSucceedCt,
TryEnqueueFailCt,
TryEnqueueWaitSucceedCt,
TryEnqueueWaitFailCt,
DequeueCt,
DequeueExCt,
RemoveCt,
RemovedCt
};
public:
static void Demo()
{
Console::WriteLine("Working...");
for(int i = 0; i < 3; i++)
{
Thread^ t = gcnew Thread(gcnew ParameterizedThreadStart(Example::ThreadProc));
t->Start(i);
Interlocked::Increment(threadsRunning);
}
};
};
void main()
{
Example::Demo();
}
/* This example produces output similar to the following:
Working...
Thread 1 Thread 2 Thread 3 Total
Enqueue 274718 513514 337895 1126127
TryEnqueue succeeded 274502 513516 337480 1125498
TryEnqueue failed 119 235 141 495
TryEnqueue(T, wait) succeeded 274552 513116 338532 1126200
TryEnqueue(T, wait) failed 0 1 0 1
Dequeue attempts 824038 1541866 1015006 3380910
Dequeue exceptions 12828 23416 14799 51043
Remove operations 68746 128218 84306 281270
Queue elements removed 11464 22024 14470 47958
Queue elements removed 2921 4690 2982 10593
*/
using System;
using System.Threading;
using System.Collections.Generic;
using System.Text;
class SafeQueue<T>
{
// A queue that is protected by Monitor.
private Queue<T> m_inputQueue = new Queue<T>();
// Lock the queue and add an element.
public void Enqueue(T qValue)
{
// Request the lock, and block until it is obtained.
Monitor.Enter(m_inputQueue);
try
{
// When the lock is obtained, add an element.
m_inputQueue.Enqueue(qValue);
}
finally
{
// Ensure that the lock is released.
Monitor.Exit(m_inputQueue);
}
}
// Try to add an element to the queue: Add the element to the queue
// only if the lock is immediately available.
public bool TryEnqueue(T qValue)
{
// Request the lock.
if (Monitor.TryEnter(m_inputQueue))
{
try
{
m_inputQueue.Enqueue(qValue);
}
finally
{
// Ensure that the lock is released.
Monitor.Exit(m_inputQueue);
}
return true;
}
else
{
return false;
}
}
// Try to add an element to the queue: Add the element to the queue
// only if the lock becomes available during the specified time
// interval.
public bool TryEnqueue(T qValue, int waitTime)
{
// Request the lock.
if (Monitor.TryEnter(m_inputQueue, waitTime))
{
try
{
m_inputQueue.Enqueue(qValue);
}
finally
{
// Ensure that the lock is released.
Monitor.Exit(m_inputQueue);
}
return true;
}
else
{
return false;
}
}
// Lock the queue and dequeue an element.
public T Dequeue()
{
T retval;
// Request the lock, and block until it is obtained.
Monitor.Enter(m_inputQueue);
try
{
// When the lock is obtained, dequeue an element.
retval = m_inputQueue.Dequeue();
}
finally
{
// Ensure that the lock is released.
Monitor.Exit(m_inputQueue);
}
return retval;
}
// Delete all elements that equal the given object.
public int Remove(T qValue)
{
int removedCt = 0;
// Wait until the lock is available and lock the queue.
Monitor.Enter(m_inputQueue);
try
{
int counter = m_inputQueue.Count;
while (counter > 0)
// Check each element.
{
T elem = m_inputQueue.Dequeue();
if (!elem.Equals(qValue))
{
m_inputQueue.Enqueue(elem);
}
else
{
// Keep a count of items removed.
removedCt += 1;
}
counter = counter - 1;
}
}
finally
{
// Ensure that the lock is released.
Monitor.Exit(m_inputQueue);
}
return removedCt;
}
// Print all queue elements.
public string PrintAllElements()
{
StringBuilder output = new StringBuilder();
// Lock the queue.
Monitor.Enter(m_inputQueue);
try
{
foreach( T elem in m_inputQueue )
{
// Print the next element.
output.AppendLine(elem.ToString());
}
}
finally
{
// Ensure that the lock is released.
Monitor.Exit(m_inputQueue);
}
return output.ToString();
}
}
public class Example
{
private static SafeQueue<int> q = new SafeQueue<int>();
private static int threadsRunning = 0;
private static int[][] results = new int[3][];
static void Main()
{
Console.WriteLine("Working...");
for(int i = 0; i < 3; i++)
{
Thread t = new Thread(ThreadProc);
t.Start(i);
Interlocked.Increment(ref threadsRunning);
}
}
private static void ThreadProc(object state)
{
DateTime finish = DateTime.Now.AddSeconds(10);
Random rand = new Random();
int[] result = { 0, 0, 0, 0, 0, 0, 0, 0, 0 };
int threadNum = (int) state;
while (DateTime.Now < finish)
{
int what = rand.Next(250);
int how = rand.Next(100);
if (how < 16)
{
q.Enqueue(what);
result[(int)ThreadResultIndex.EnqueueCt] += 1;
}
else if (how < 32)
{
if (q.TryEnqueue(what))
{
result[(int)ThreadResultIndex.TryEnqueueSucceedCt] += 1;
}
else
{
result[(int)ThreadResultIndex.TryEnqueueFailCt] += 1;
}
}
else if (how < 48)
{
// Even a very small wait significantly increases the success
// rate of the conditional enqueue operation.
if (q.TryEnqueue(what, 10))
{
result[(int)ThreadResultIndex.TryEnqueueWaitSucceedCt] += 1;
}
else
{
result[(int)ThreadResultIndex.TryEnqueueWaitFailCt] += 1;
}
}
else if (how < 96)
{
result[(int)ThreadResultIndex.DequeueCt] += 1;
try
{
q.Dequeue();
}
catch
{
result[(int)ThreadResultIndex.DequeueExCt] += 1;
}
}
else
{
result[(int)ThreadResultIndex.RemoveCt] += 1;
result[(int)ThreadResultIndex.RemovedCt] += q.Remove(what);
}
}
results[threadNum] = result;
if (0 == Interlocked.Decrement(ref threadsRunning))
{
StringBuilder sb = new StringBuilder(
" Thread 1 Thread 2 Thread 3 Total\n");
for(int row = 0; row < 9; row++)
{
int total = 0;
sb.Append(titles[row]);
for(int col = 0; col < 3; col++)
{
sb.Append(String.Format("{0,9}", results[col][row]));
total += results[col][row];
}
sb.AppendLine(String.Format("{0,9}", total));
}
Console.WriteLine(sb.ToString());
}
}
private static string[] titles = {
"Enqueue ",
"TryEnqueue succeeded ",
"TryEnqueue failed ",
"TryEnqueue(T, wait) succeeded ",
"TryEnqueue(T, wait) failed ",
"Dequeue attempts ",
"Dequeue exceptions ",
"Remove operations ",
"Queue elements removed "};
private enum ThreadResultIndex
{
EnqueueCt,
TryEnqueueSucceedCt,
TryEnqueueFailCt,
TryEnqueueWaitSucceedCt,
TryEnqueueWaitFailCt,
DequeueCt,
DequeueExCt,
RemoveCt,
RemovedCt
};
}
/* This example produces output similar to the following:
Working...
Thread 1 Thread 2 Thread 3 Total
Enqueue 277382 515209 308464 1101055
TryEnqueue succeeded 276873 514621 308099 1099593
TryEnqueue failed 109 181 134 424
TryEnqueue(T, wait) succeeded 276913 514434 307607 1098954
TryEnqueue(T, wait) failed 2 0 0 2
Dequeue attempts 830980 1544081 924164 3299225
Dequeue exceptions 12102 21589 13539 47230
Remove operations 69550 129479 77351 276380
Queue elements removed 11957 22572 13043 47572
*/
Imports System.Threading
Imports System.Collections.Generic
Imports System.Text
Class SafeQueue(Of T)
' A queue that is protected by Monitor.
Private m_inputQueue As New Queue(Of T)
' Lock the queue and add an element.
Public Sub Enqueue(ByVal qValue As T)
' Request the lock, and block until it is obtained.
Monitor.Enter(m_inputQueue)
Try
' When the lock is obtained, add an element.
m_inputQueue.Enqueue(qValue)
Finally
' Ensure that the lock is released.
Monitor.Exit(m_inputQueue)
End Try
End Sub
' Try to add an element to the queue: Add the element to the queue
' only if the lock is immediately available.
Public Function TryEnqueue(ByVal qValue As T) As Boolean
' Request the lock.
If Monitor.TryEnter(m_inputQueue) Then
Try
m_inputQueue.Enqueue(qValue)
Finally
' Ensure that the lock is released.
Monitor.Exit(m_inputQueue)
End Try
Return True
Else
Return False
End If
End Function
' Try to add an element to the queue: Add the element to the queue
' only if the lock becomes available during the specified time
' interval.
Public Function TryEnqueue(ByVal qValue As T, ByVal waitTime As Integer) As Boolean
' Request the lock.
If Monitor.TryEnter(m_inputQueue, waitTime) Then
Try
m_inputQueue.Enqueue(qValue)
Finally
' Ensure that the lock is released.
Monitor.Exit(m_inputQueue)
End Try
Return True
Else
Return False
End If
End Function
' Lock the queue and dequeue an element.
Public Function Dequeue() As T
Dim retval As T
' Request the lock, and block until it is obtained.
Monitor.Enter(m_inputQueue)
Try
' When the lock is obtained, dequeue an element.
retval = m_inputQueue.Dequeue()
Finally
' Ensure that the lock is released.
Monitor.Exit(m_inputQueue)
End Try
Return retval
End Function
' Delete all elements that equal the given object.
Public Function Remove(ByVal qValue As T) As Integer
Dim removedCt As Integer = 0
' Wait until the lock is available and lock the queue.
Monitor.Enter(m_inputQueue)
Try
Dim counter As Integer = m_inputQueue.Count
While (counter > 0)
'Check each element.
Dim elem As T = m_inputQueue.Dequeue()
If Not elem.Equals(qValue) Then
m_inputQueue.Enqueue(elem)
Else
' Keep a count of items removed.
removedCt += 1
End If
counter = counter - 1
End While
Finally
' Ensure that the lock is released.
Monitor.Exit(m_inputQueue)
End Try
Return removedCt
End Function
' Print all queue elements.
Public Function PrintAllElements() As String
Dim output As New StringBuilder()
'Lock the queue.
Monitor.Enter(m_inputQueue)
Try
For Each elem As T In m_inputQueue
' Print the next element.
output.AppendLine(elem.ToString())
Next
Finally
' Ensure that the lock is released.
Monitor.Exit(m_inputQueue)
End Try
Return output.ToString()
End Function
End Class
Public Class Example
Private Shared q As New SafeQueue(Of Integer)
Private Shared threadsRunning As Integer = 0
Private Shared results(2)() As Integer
Friend Shared Sub Main()
Console.WriteLine("Working...")
For i As Integer = 0 To 2
Dim t As New Thread(AddressOf ThreadProc)
t.Start(i)
Interlocked.Increment(threadsRunning)
Next i
End Sub
Private Shared Sub ThreadProc(ByVal state As Object)
Dim finish As DateTime = DateTime.Now.AddSeconds(10)
Dim rand As New Random()
Dim result() As Integer = { 0, 0, 0, 0, 0, 0, 0, 0, 0 }
Dim threadNum As Integer = CInt(state)
While (DateTime.Now < finish)
Dim what As Integer = rand.Next(250)
Dim how As Integer = rand.Next(100)
If how < 16 Then
q.Enqueue(what)
result(ThreadResultIndex.EnqueueCt) += 1
Else If how < 32 Then
If q.TryEnqueue(what)
result(ThreadResultIndex.TryEnqueueSucceedCt) += 1
Else
result(ThreadResultIndex.TryEnqueueFailCt) += 1
End If
Else If how < 48 Then
' Even a very small wait significantly increases the success
' rate of the conditional enqueue operation.
If q.TryEnqueue(what, 10)
result(ThreadResultIndex.TryEnqueueWaitSucceedCt) += 1
Else
result(ThreadResultIndex.TryEnqueueWaitFailCt) += 1
End If
Else If how < 96 Then
result(ThreadResultIndex.DequeueCt) += 1
Try
q.Dequeue()
Catch
result(ThreadResultIndex.DequeueExCt) += 1
End Try
Else
result(ThreadResultIndex.RemoveCt) += 1
result(ThreadResultIndex.RemovedCt) += q.Remove(what)
End If
End While
results(threadNum) = result
If 0 = Interlocked.Decrement(threadsRunning) Then
Dim sb As New StringBuilder( _
" Thread 1 Thread 2 Thread 3 Total" & vbLf)
For row As Integer = 0 To 8
Dim total As Integer = 0
sb.Append(titles(row))
For col As Integer = 0 To 2
sb.Append(String.Format("{0,9}", results(col)(row)))
total += results(col)(row)
Next col
sb.AppendLine(String.Format("{0,9}", total))
Next row
Console.WriteLine(sb.ToString())
End If
End Sub
Private Shared titles() As String = { _
"Enqueue ", _
"TryEnqueue succeeded ", _
"TryEnqueue failed ", _
"TryEnqueue(T, wait) succeeded ", _
"TryEnqueue(T, wait) failed ", _
"Dequeue attempts ", _
"Dequeue exceptions ", _
"Remove operations ", _
"Queue elements removed " _
}
Private Enum ThreadResultIndex
EnqueueCt
TryEnqueueSucceedCt
TryEnqueueFailCt
TryEnqueueWaitSucceedCt
TryEnqueueWaitFailCt
DequeueCt
DequeueExCt
RemoveCt
RemovedCt
End Enum
End Class
' This example produces output similar to the following:
'
'Working...
' Thread 1 Thread 2 Thread 3 Total
'Enqueue 294357 512164 302838 1109359
'TryEnqueue succeeded 294486 512403 303117 1110006
'TryEnqueue failed 108 234 127 469
'TryEnqueue(T, wait) succeeded 294259 512796 302556 1109611
'TryEnqueue(T, wait) failed 1 1 1 3
'Dequeue attempts 882266 1537993 907795 3328054
'Dequeue exceptions 12691 21474 13480 47645
'Remove operations 74059 128715 76187 278961
'Queue elements removed 12667 22606 13219 48492
Comentários
Se for bem-sucedido, esse método adquire um bloqueio exclusivo no obj parâmetro.If successful, this method acquires an exclusive lock on the obj parameter. Esse método retorna imediatamente, independentemente de o bloqueio estar ou não disponível.This method returns immediately, whether or not the lock is available.
Esse método é semelhante a Enter , mas nunca bloqueará o thread atual.This method is similar to Enter, but it will never block the current thread. Se o thread não puder entrar sem bloqueio, o método retornará false, .If the thread cannot enter without blocking, the method returns false,.
Observação
Use Monitor para bloquear objetos (ou seja, tipos de referência), não tipos de valor.Use Monitor to lock objects (that is, reference types), not value types. Para obter detalhes, consulte o Monitor artigo.For details, see the Monitor article.
Para garantir que o thread não insira a seção crítica, você deve examinar o valor de retorno do método e executar o código na seção crítica somente se o valor de retorno for true .To ensure that the thread does not enter the critical section, you should examine the method's return value and execute code in the critical section only if its return value is true. O fragmento de código a seguir mostra o padrão usado para chamar esse método.The following code fragment shows the pattern used to call this method. Observe que você deve chamar Exit em um finally bloco para garantir que o thread de chamada libere seu bloqueio na seção crítica se ocorrer uma exceção.Note that you should call Exit in a finally block to ensure that the calling thread releases its lock on the critical section if an exception occurs.
var lockObj = new Object();
if (Monitor.TryEnter(lockObj)) {
try {
// The critical section.
}
finally {
// Ensure that the lock is released.
Monitor.Exit(lockObj);
}
}
else {
// The lock was not axquired.
}
Dim lockObj As New Object()
If Monitor.TryEnter(lockObj) Then
Try
' The critical section.
Finally
' Ensure that the lock is released.
Monitor.Exit(lockObj)
End Try
Else
' The lock was not acquired.
End If
Confira também
Aplica-se a
TryEnter(Object, Int32)
Tentativas, durante o período especificado de milésimos de segundos, para adquirir um bloqueio exclusivo no objeto especificado.Attempts, for the specified number of milliseconds, to acquire an exclusive lock on the specified object.
public:
static bool TryEnter(System::Object ^ obj, int millisecondsTimeout);
public static bool TryEnter (object obj, int millisecondsTimeout);
static member TryEnter : obj * int -> bool
Public Shared Function TryEnter (obj As Object, millisecondsTimeout As Integer) As Boolean
Parâmetros
- obj
- Object
O objeto no qual adquirir o bloqueio.The object on which to acquire the lock.
- millisecondsTimeout
- Int32
O número de milésimos de segundos de espera do bloqueio.The number of milliseconds to wait for the lock.
Retornos
true se o thread atual adquirir o bloqueio; caso contrário, false.true if the current thread acquires the lock; otherwise, false.
Exceções
O parâmetro obj é null.The obj parameter is null.
millisecondsTimeout é negativo e diferente de Infinite.millisecondsTimeout is negative, and not equal to Infinite.
Comentários
Se o millisecondsTimeout parâmetro for igual a Infinite , esse método será equivalente a Enter .If the millisecondsTimeout parameter equals Infinite, this method is equivalent to Enter. Se for millisecondsTimeout igual a 0, esse método será equivalente a TryEnter .If millisecondsTimeout equals 0, this method is equivalent to TryEnter.
Observação
Use Monitor para bloquear objetos (ou seja, tipos de referência), não tipos de valor.Use Monitor to lock objects (that is, reference types), not value types. Para obter detalhes, consulte o Monitor artigo.For details, see the Monitor article.
Para garantir que o thread não insira a seção crítica, você deve examinar o valor de retorno do método e executar o código na seção crítica somente se o valor de retorno for true .To ensure that the thread does not enter the critical section, you should examine the method's return value and execute code in the critical section only if its return value is true. O fragmento de código a seguir mostra o padrão usado para chamar esse método.The following code fragment shows the pattern used to call this method. Observe que você deve chamar Exit em um finally bloco para garantir que o thread de chamada libere seu bloqueio na seção crítica se ocorrer uma exceção.Note that you should call Exit in a finally block to ensure that the calling thread releases its lock on the critical section if an exception occurs.
var lockObj = new Object();
int timeout = 500;
if (Monitor.TryEnter(lockObj, timeout)) {
try {
// The critical section.
}
finally {
// Ensure that the lock is released.
Monitor.Exit(lockObj);
}
}
else {
// The lock was not acquired.
}
Dim lockObj As New Object()
Dim timeout As Integer = 500
If Monitor.TryEnter(lockObj, timeout) Then
Try
' The critical section.
Finally
' Ensure that the lock is released.
Monitor.Exit(lockObj)
End Try
Else
' The lock was not acquired.
End If