ordering example: fixed

threads-bugs/Makefile

@@ -9,7 +9,8 @@ endif
 
 SRCS   := atomicity.c \
 	atomicity_fixed.c \
-	ordering.c
+	ordering.c \
+	ordering_fixed.c
 
 OBJS   := ${SRCS:c=o}
 PROGS  := ${SRCS:.c=}

threads-bugs/README.md

@@ -7,6 +7,13 @@ Type `make` to build all examples.
 ## Atomicity Failure
 
 - `atomicity.c`: Shows how uncareful check-then-use can crash code
+- `atomicity_fixed.c`: Shows how to fix the problem with a lock
+
+## Ordering Violation
+
+- `ordering.c`: Shows the ordering problem from the book chapter
+- `ordering_fixed.c`: Shows how to fix the problem with a condition variable
+
 
 
 

threads-bugs/ordering_fixed.c

@@ -0,0 +1,66 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <unistd.h>
+
+#include "common.h"
+#include "common_threads.h"
+
+#define PR_STATE_INIT (0)
+
+typedef struct {
+    pthread_t Tid;
+    int State;
+} pr_thread_t;
+
+pr_thread_t *PR_CreateThread(void *(*start_routine)(void *)) {
+    pr_thread_t *p = malloc(sizeof(pr_thread_t));
+    if (p == NULL) 
+	return NULL;
+    p->State = PR_STATE_INIT;
+    Pthread_create(&p->Tid, NULL, start_routine, NULL); 
+    // turn the sleep off to avoid the fault, sometimes...
+    sleep(1);
+    return p;
+}
+
+void PR_WaitThread(pr_thread_t *p) {
+    Pthread_join(p->Tid, NULL); 
+}
+
+pr_thread_t *mThread;
+
+pthread_mutex_t mtLock = PTHREAD_MUTEX_INITIALIZER;
+pthread_cond_t  mtCond = PTHREAD_COND_INITIALIZER;
+int mtInit = 0;
+
+void *mMain(void *arg) {
+    printf("mMain: begin\n");
+
+    // wait for thread structure to be initialized
+    Pthread_mutex_lock(&mtLock);
+    while (mtInit == 0)
+	Pthread_cond_wait(&mtCond, &mtLock);
+    Pthread_mutex_unlock(&mtLock);
+
+    int mState = mThread->State;
+    printf("mMain: state is %d\n", mState);
+    return NULL;
+}
+
+
+int main(int argc, char *argv[]) {
+    printf("ordering: begin\n");
+    mThread = PR_CreateThread(mMain);
+
+    // signal: thread has been created, and mThread initialized
+    Pthread_mutex_lock(&mtLock);
+    mtInit = 1;
+    Pthread_cond_signal(&mtCond);
+    Pthread_mutex_unlock(&mtLock);
+
+    PR_WaitThread(mThread);
+    printf("ordering: end\n");
+    return 0;
+}
+