[Qemu-devel] [PATCH 07/21] add assertions on the owner of a QemuMutex

[Paolo Bonzini <pbonzini@redhat.com>]

These are already present in the Win32 implementation, add them to
the pthread wrappers as well.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 qemu-thread-posix.c |   27 +++++++++++++++++++++++++--
 qemu-thread-posix.h |    1 +
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/qemu-thread-posix.c b/qemu-thread-posix.c
index 28b3f80..2176f81 100644
--- a/qemu-thread-posix.c
+++ b/qemu-thread-posix.c
@@ -16,9 +16,12 @@
 #include <time.h>
 #include <signal.h>
 #include <stdint.h>
+#include <assert.h>
 #include <string.h>
 #include "qemu-thread.h"
 
+static pthread_t pthread_null;
+
 static void error_exit(int err, const char *msg)
 {
     fprintf(stderr, "qemu: %s: %s\n", msg, strerror(err));
@@ -28,8 +31,13 @@ static void error_exit(int err, const char *msg)
 void qemu_mutex_init(QemuMutex *mutex)
 {
     int err;
+    pthread_mutexattr_t mutexattr;
 
-    err = pthread_mutex_init(&mutex->lock, NULL);
+    mutex->owner = pthread_null;
+    pthread_mutexattr_init(&mutexattr);
+    pthread_mutexattr_settype(&mutexattr, PTHREAD_MUTEX_ERRORCHECK);
+    err = pthread_mutex_init(&mutex->lock, &mutexattr);
+    pthread_mutexattr_destroy(&mutexattr);
     if (err)
         error_exit(err, __func__);
 }
@@ -48,13 +56,20 @@ void qemu_mutex_lock(QemuMutex *mutex)
     int err;
 
     err = pthread_mutex_lock(&mutex->lock);
+    mutex->owner = pthread_self();
     if (err)
         error_exit(err, __func__);
 }
 
 int qemu_mutex_trylock(QemuMutex *mutex)
 {
-    return pthread_mutex_trylock(&mutex->lock);
+    int err;
+    err = pthread_mutex_trylock(&mutex->lock);
+    if (err == 0) {
+        mutex->owner = pthread_self();
+    }
+
+    return !!err;
 }
 
 static void timespec_add_ms(struct timespec *ts, uint64_t msecs)
@@ -85,6 +100,11 @@ void qemu_mutex_unlock(QemuMutex *mutex)
 {
     int err;
 
+    /* An EDEADLOCK would arrive after we reset the owner.  So this
+       assert is for ease of debugging (it lets you see what is the
+       actual owner.  */
+    assert(pthread_equal(mutex->owner, pthread_self()));
+    mutex->owner = pthread_null;
     err = pthread_mutex_unlock(&mutex->lock);
     if (err)
         error_exit(err, __func__);
@@ -130,7 +150,10 @@ void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
 {
     int err;
 
+    assert(pthread_equal(mutex->owner, pthread_self()));
+    mutex->owner = pthread_null;
     err = pthread_cond_wait(&cond->cond, &mutex->lock);
+    mutex->owner = pthread_self();
     if (err)
         error_exit(err, __func__);
 }
diff --git a/qemu-thread-posix.h b/qemu-thread-posix.h
index 7af371c..11978db 100644
--- a/qemu-thread-posix.h
+++ b/qemu-thread-posix.h
@@ -4,6 +4,7 @@
 
 struct QemuMutex {
     pthread_mutex_t lock;
+    pthread_t owner;
 };
 
 struct QemuCond {
-- 
1.7.3.5