Question

我有以下涉及pthread和semaphore的简单程序。我在osx Maverck 10.9。我使用makefile来编译程序（而不是xcode）。我用c ++ 11。

#include <pthread.h>
#include <semaphore.h>
#include <cassert>
#include <iostream>

#define ASSERT(a) if(!(a)) abort

using namespace std;

sem_t countMutex;
int myCount=0;

void *doThread(void *data) {
    int *pi = reinterpret_cast<int *>(data);
    sem_wait(&countMutex);
    for(int i =0 ;i < 100; ++i) {
        myCount += 1;
    }
    sem_post(&countMutex);
    pthread_exit( NULL );
}

void LaunchThread() {
    const int kNumThreads = 10;
    pthread_t tids[kNumThreads];
    int threadData[kNumThreads];
    pthread_attr_t attr;
    pthread_t tid;
    int retVal=0;
    retVal = pthread_attr_init(&attr);
    ASSERT(retVal == 0);
    retVal = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE );
    ASSERT(retVal == 0);
    sem_init(&countMutex, 0, 1);
    myCount = 0;
    for(int i=0; i < kNumThreads; ++i) {
        threadData[i] = i;
        retVal = pthread_create( &tids[i], &attr, &doThread, &threadData[i]);
        if(retVal != 0) {
            cerr << "cannot create thread" << endl;
            return;
        }
    }

    retVal = pthread_attr_destroy(&attr);
    ASSERT(retVal == 0);
    void *status = NULL;
    for(int i=0; i < kNumThreads; ++i) {
        retVal = pthread_join( tids[i], &status);
        if(retVal != 0) {
            cerr << "cannot join ghread " << i << ", " << tids[i] << endl;
            return;
        }
        cout << "completed thread " << i << ", " << tids[i] << endl;
    }
    cout << "value of myCount: " <<  myCount << endl;
    sem_destroy(&countMutex);
    //sem_unlink(&countMutex);
    pthread_exit( NULL );
}
int main( int argc, char **argv) {
    LaunchThread();
    return 0;
}

用于编译它的makefile是

CXX=clang++
CXXFLAGS=-g -Wall -Wno-deprecated -std=c++11 -pthread  -D DEBUG -g3 $(INCLUDES)
LDFLAGS=$(LIBS)

OBJS=main.o
PROG=test

all: $(PROG)


$(PROG): $(OBJS)
$(CXX) -v -o $(PROG) main.o $(LDFLAGS)

%.o: %.cpp
$(CXX) -c $(CXXFLAGS) $<

clean:
rm $(OBJS); rm test

该程序应该为myCount报告的值为1000。但是在多次运行中是不一致的。

例如：

completed thread 0, 0x107dca000
completed thread 1, 0x107e4d000
completed thread 2, 0x107ed0000
completed thread 3, 0x107f53000
completed thread 4, 0x107fd6000
completed thread 5, 0x108059000
completed thread 6, 0x1080dc000
completed thread 7, 0x10815f000
completed thread 8, 0x1081e2000
completed thread 9, 0x108265000
value of myCount: 900

Answer 1

OSX不支持未命名的POSIX信号量。如果您检查返回代码，则会看到sem_init失败并显示错误。您需要使用命名信号量。

使用sem_open代替sem_init。请勿使用sem_destroy，而应使用sem_close和sem_unlink。

你会很高兴。

在osx maverick 10.9中，pthread和信号量不适合我

1 个答案: