pthread和信号量在osx maverick 10.9中对我不起作用

pthread and semaphore not working for me in osx maverick 10.9

本文关键字：不起作用 maverick 信号量 osx pthread      更新时间：2023-10-16

我有以下涉及pthread和信号量的简单程序。我在osx Maverick 10.9。我使用makefile来编译程序(而不是xcode(。我使用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;
}

编译这个的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

程序应该报告myCount的值为1000。但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

OSX不支持未命名的POSIX信号量。如果您检查您的返回代码，您将看到sem_init失败，并在这些行中出现错误。您需要使用命名信号量。

使用sem_open而不是sem_init。不要使用sem_destroy，而是使用sem_close和sem_unlink。

你可以走了。

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