source36

unit EventSync;

{ Martin Harvey 5/6/2000 }

interface

uses Windows;

type
TEventSynchronizer = class(TObject)
private
FDataLock, FWriteLock: TRTLCriticalSection;
FReaders, FWriters: integer;
FNoReaders, FNoWriters: THandle;
protected
public
constructor Create;
destructor Destroy; override;
procedure StartRead;
procedure StartWrite;
procedure EndRead;
procedure EndWrite;
published
end;

implementation

constructor TEventSynchronizer.Create;
begin
inherited Create;
InitializeCriticalSection(FDataLock);
InitializeCriticalSection(FWriteLock);
FNoReaders := CreateEvent(nil, true, true, nil);
FNoWriters := CreateEvent(nil, true, true, nil);
end;

destructor TEventSynchronizer.Destroy;
begin
DeleteCriticalSection(FDataLock);
DeleteCriticalSection(FWriteLock);
CloseHandle(FNoReaders);
CloseHandle(FNoWriters);
inherited Destroy;
end;

procedure TEventSynchronizer.StartRead;

var
Block: boolean;

begin
EnterCriticalSection(FDatalock);
if FReaders = 0 then
ResetEvent(FNoReaders);
Inc(FReaders);
Block := FWriters > 0;
LeaveCriticalSection(FDataLock);
if Block then
WaitForSingleObject(FNoWriters, INFINITE);
end;

procedure TEventSynchronizer.StartWrite;

var
Block: boolean;

begin
EnterCriticalSection(FDataLock);
if FWriters = 0 then
ResetEvent(FNoWriters);
Inc(FWriters);
Block := FReaders > 0;
LeaveCriticalSection(FDataLock);
if Block then
WaitForSingleObject(FNoReaders, INFINITE);
EnterCriticalSection(FWriteLock);
end;

procedure TEventSynchronizer.EndRead;
begin
EnterCriticalSection(FDataLock);
Dec(FReaders);
if FReaders = 0 then
SetEvent(FNoReaders);
LeaveCriticalSection(FDataLock);
end;

procedure TEventSynchronizer.EndWrite;
begin
LeaveCriticalSection(FWriteLock);
EnterCriticalSection(FDataLock);
Dec(FWriters);
if FWriters = 0 then
SetEvent(FNoWriters);
LeaveCriticalSection(FDataLock);
end;

end.

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